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Mechanisms of Soil Fertility: Looking at Biologicals and MOA
Brian Arnall, Oklahoma State University Precision Nutrient Management
The use of biological products in commercial agriculture has expanded rapidly, with large corporations entering a space once dominated by smaller groups. This has created an arms race, with nearly every company offering a biological product. Over the past twenty years, I have had the opportunity to test products from the biggest groups with billions in backing, to solutions raised in stock tanks delivered in Braums milk jugs. It is critical to understand what is in the jug and the biological function it is expected to perform. Like herbicides, knowing the mode of action determines whether the product fits the intended purpose. No different than herbicides and knowing mode of actions. It’s important to know and understand that if you are trying to kill ryegrass 2.4-D, a broadleaf herbicide is not the right answer.
So what are we working with that’s in these products?
My approach has been to classify the products by operation not by species or genre. Doing so I have grouped products into five biological classifications and a sixth group, which is often in concluded in conversations.
Decomposers / Organic Matter Mineralizers
Nitrogen Fixers (Symbiotic and Associative)
Symbiotic Root Associations (Mycorrhizae, PGPR)
Nutrient Solubilizers
Biological Pest Control
Plant Growth Regulators (Hormonal Effects)
So, let’s dig into each of the mechanisms.
Decomposers / Organic Matter Mineralizers
Decomposition is carried out by a diverse group of organisms including fungi (e.g., Trichoderma, Aspergillus), bacteria (e.g., Bacillus, Pseudomonas), and actinomycetes (e.g., Streptomyces), each contributing to the breakdown of organic materials through different enzymatic pathways. This process of decomposing organic matter releases the nutrients tied up into plant available forms. The release of nitrogen is usually first thought, but this process adds significant amounts of potassium, calcium, and magnesium.
The process occurs both in the soil and on the soil surface. While it seems simple in application though this is a complex process. Let’s start with the soil pool, triggering decomposition of a system where the previous crop was wheat is significantly different than following corn. Following wheat, the carbon nitrogen ratio will be very high (see sugar blog), so while decomposition will release cations such as potassium and calcium, it is very likely to immobilize and residual nitrogen in the system. However, in fields that previously had corn the carbon to nitrogen ratio is much closer and the probability of seeing nitrogen release is much higher (Kuzyakov & Blagodatskaya, 2015). The process is similar for surface residues, but the rate is heavily controlled by rainfall. While both the soil and surface systems require moisture for the process to progress, the surface moisture is much more dynamic with frequent wetting and drying. Rain or irrigation is also needed to move the nutrients into the root zone.
One aspect of increasing decomposition of OM that I do not have a handle on is the long-term impact of expediting OM breakdown in and on the soil, especially in the central plains. As mentioned in the sugar blog, you would hope that the increase in nutrients from OM decomposition would increase plant growth enough to replenish the OM that was burned up. One caveat to this is that the decomposition would have to add nutrients that are deficient. Otherwise, there is no increase in plant growth and hypothetically the system is not net negative on OM. When it comes to decomposing surface residue, I have always been a bit hesitant in Oklahoma as I see having surface coverage to preserve soil moisture typically has a greater value than the nutrients from the residue.
Nitrogen Fixers (Symbiotic and Associative)
Nitrogen fixation is carried out by both symbiotic organisms such as Rhizobium and Bradyrhizobium, which form nodules on plant roots and supply significant nitrogen, and associative organisms such as Azospirillum and Azotobacter, which reside in the rhizosphere and contribute smaller, more variable amounts of nitrogen. Symbiotic nitrogen fixation, such as we have come to expect from legumes, is tightly regulated by the plant, with carbon supplied to the microbe in exchange for fixed nitrogen, making it one of the most efficient biological nitrogen inputs in agriculture.
Associative nitrogen fixation is not directly coupled to plant demand, and nitrogen contributions are typically limited by carbon availability and environmental conditions (Kennedy et al., 2004). While these organisms possess the ability to fix atmospheric nitrogen, the magnitude of nitrogen contribution, particularly from non-symbiotic systems, is highly variable and often limited under field conditions. We know that in soybean nodulation is greatly reduced when excess nitrogen is present in the soil, basically the plant does not need rhizobia, so it does not trigger symbiosis. I expect that as we move symbiotic fixation out of legumes that this mechanism does not change. Finally fixed N is no different than fertilizer N, if you add more then the crop needs, its lost. Therefore, if I am planning to use a N fixer, I would significantly reduce the amount of fertilizer N apply well below crop demand. Otherwise, the money spent on the N fixer is a waste. The only argument I have heard for this is the security blanket, making sure that if more is needed than normally the system is covered. But I circle back to the question about a system with high levels of residual N and rhizobium nodulation.
Symbiotic Root Associations (Mycorrhizae, PGPR)
Symbiotic root associations include arbuscular mycorrhizal fungi (e.g., Rhizophagus, Funneliformis) that extend the effective root system and improve nutrient uptake, particularly phosphorus, as well as plant growth-promoting rhizobacteria (e.g., Pseudomonas, Bacillus) that influence root development and plant signaling through multiple biochemical pathways (Smith & Read, 2008). In my visits with soil microbiologist, I have been left with the understanding that these relationships are not generic, but quite specific. There is significant influence of genotype and environment. And even more interesting is that the majority expect that the plant needs to signal for this relationship to happen.
The effectiveness of these associations is highly dependent on soil conditions, existing microbial communities, and nutrient availability, with responses often diminishing in systems where nutrients are not limited or where native populations are already established. I was able to follow along with some work down at OSU a few years back that was working with sorghum looking for symbiotic relationships to improve water and nutrient uptake specifically phosphorus. The work was successful, the researchers were able to identify a AMF that created a symbiotic relationship with sorghum, with a few caveats. First land race cultivars had a much higher incidence of symbiosis. For the landraces it worked well in extremely nutrient depleted soils and any additions of N or P reduced forage yield over the none. In the end the researchers were able to show improved the grain yield in landraces above fertilized, but these yields did equal fertilized hybrids. This work had great impact on small holders in developing counties with limited resources.
Nutrient Solubilizers
Nutrient solubilization is carried out by organisms such as Bacillus, Pseudomonas, and Aspergillus, which increase nutrient availability through mechanisms including organic acid production, proton release, and chelation, allowing nutrients like phosphorus and micronutrients to become more accessible in the rhizosphere.
Phosphorus-solubilizing fungi, such as Aspergillus and Penicillium, function similarly to bacterial solubilizers but are often more effective at producing strong organic acids. These acids can lower pH in localized zones and release phosphorus from mineral-bound forms, particularly in soils with high fixation capacity. Fungal systems can operate across a wider range of environmental conditions and may play a larger role in longer-term phosphorus cycling. However, as with bacterial systems, these effects are generally localized and dependent on soil chemistry (Richardson et al., 2009). I tend to see these having the greatest benefits in systems that have historically received manures or long-term applications of fertilizer P. I do not believe this is a good fit for soils with limited available phosphorus, as it is trying to focus the soil into something, it does not want to do or have too spare.
Potassium-solubilizing organisms, including species such as Bacillus mucilaginosus and Frateuria aurantia, contribute to the release of potassium from primary minerals like feldspars and micas. These microbes facilitate mineral weathering through acidification and chelation processes that slowly break down mineral structures. While the mechanism is well understood, the rate of potassium release is typically slow relative to crop demand. As a result, these organisms are more influential in long-term soil development than in short-term fertility management (Sheng & He, 2006).
Micronutrient-mobilizing organisms, particularly Pseudomonas and Bacillus species, enhance availability through the production of siderophores and other chelating compounds. These molecules bind metals such as iron and zinc, increasing their solubility and facilitating uptake in the rhizosphere. This process is especially important in soils where micronutrients are present but not readily available due to chemical constraints. However, the impact is typically limited to the immediate root zone and depends on both microbial activity and soil conditions (Ahmed & Holmström, 2014).
Biological Pest Control
Biological pest control organisms, including species such as Bacillus, Pseudomonas, and Trichoderma, function by suppressing pathogens through several well-documented mechanisms. These include the production of inhibitory compounds, competition for space and nutrients, direct antagonism of pathogens, and the activation of plant defense systems through induced systemic resistance. While these mechanisms are well established under controlled conditions, their effectiveness in field environments is highly dependent on environmental conditions, pathogen pressure, and the ability of the organism to persist and colonize the soil or plant surface (Lugtenberg & Kamilova, 2009).
I’ve been working with a lot of folks from Brazil who historically make four to six nemacide applications in soybean, but utilizing Pseudomanas they have been able to reduce that number by half or more. The caveat, as I understand, the application rates needed are significantly higher than anything I have seen in the US. If you look through the literature, you are seeing more and more documentation of this such as Li et al. 2022. But as Spescha et al. (2023) documented, different biological control agents operate through complementary mechanisms, including infection, toxin production, and host targeting. However, effectiveness depended on environmental conditions and interactions among organisms, reinforcing that biological control outcomes are system-dependent rather than universally consistent.
Plant Growth Regulators (Hormonal Effects)
This group differs slightly, as the primary effect is not direct nutrient cycling but modification of plant physiological response. This group is one I hold the greatest expectations for. I mean we have been using PGRs in crop production for decades, we just did not have an inkling of how many PGRs exist.
Plant growth regulator effects are associated with organisms such as Azospirillum, Bacillus, and Pseudomonas, which can influence plant development through the production of phytohormones and related compounds. These microbes produce substances such as auxins, cytokinins, and gibberellins that alter root architecture and plant growth patterns, and in some cases reduce stress responses through enzymes like ACC deaminase. Rather than supplying nutrients directly, these organisms modify how plants respond to their environment and utilize available resources. However, just like everything previously discussed the magnitude of response is often subtle and highly dependent on environmental conditions and crop system interactions (Glick, 2012).
Final thoughts.
There is one situation that pops up that I do not agree with, based upon my limited understanding of soil microbiology. Its adding more of what is already there. The soil system is a dynamic system. While there are population booms and bust, it supports what it is able to. Adding more of what is already there is like dropping a million rabbits into a prairie that has rabbits already. The current population is where it is because that is what the system can support. Adding means one of two things, a lot of rabbits die immediately, or they overwhelm the system and another animal species dies off due to lack of resources. Also, most microbiologists tell me the system is amazing at signaling and finding what it wants. It may take a season, but it will be there, in the quantities that soil needs, just given time.
So, the final slide in all my biological additives talks ends with this statement. My experiments show one thing. The impact of adding these products on crop yields is very consistently inconsistent. I’ve had many show a significant positive response, once. I have struggled to ever get repeated successes. It is my belief that I will have more success improving the soil biome by managing the soil (no-till, crop rotation, cover crops) than I will ever have with adding a product.
Final comment, Read the label. Many of the biological products I have tested are not singularly pure species. There are many blends of species and organisms which encompass many of the modes. A lot of these blends also contain extras such as humics, fulvics, carbohydrates, and sugars, see previous blogs.
Take-Home Messages
- Biological products function through specific mechanisms, not as broad “boosters,” and understanding that mechanism is critical to proper use.
- The presence of a biological function does not guarantee a yield response, outcomes are driven by soil, crop, and environmental conditions
- Decomposers and carbon-driven systems can immobilize or mineralize nitrogen, depending largely on residue quality and system balance
- Mycorrhizae and PGPR improve access to existing nutrients, not total nutrient supply
- Nutrient-solubilizing organisms mobilize nutrients already present in the soil
- Plant growth regulators influence plant signaling and development
- Adding biological organisms to soil does not guarantee establishment or persistence, as soil systems can regulate microbial populations.
- Management practices such as no-till, crop rotation, and cover crops are effective at improving soil biological function
- Across all biological products, mechanism exists, but response depends on the system
Any questions or comments please reachout to me @ b.arnall@okstate.edu
Citations
Ahmed, E., & Holmström, S. J. M. (2014). Siderophores in environmental research: Roles and applications. Microbial Biotechnology, 7(3), 196–208.
Glick, B. R. (2012). Plant growth-promoting bacteria: Mechanisms and applications. Scientifica, 2012, 963401
Kennedy, I. R., Choudhury, A. T. M. A., & Kecskés, M. L. (2004).
Non-symbiotic bacterial diazotrophs in crop-farming systems. Plant and Soil, 266, 65–79.
Kuzyakov, Y., & Blagodatskaya, E. (2015).
Microbial hotspots and hot moments in soil. Soil Biology and Biochemistry, 83, 184–199.
Lugtenberg, B., & Kamilova, F. (2009). Plant-growth-promoting rhizobacteria. Annual Review of Microbiology, 63, 541–556.
Richardson, A. E., Barea, J. M., McNeill, A. M., & Prigent-Combaret, C. (2009). Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth promotion by microorganisms. Plant and Soil, 321(1–2), 305–339.
Sheng, X. F., & He, L. Y. (2006). Solubilization of potassium-bearing minerals by a wild-type strain of Bacillus edaphicus and its mutants and increased potassium uptake by wheat. Canadian Journal of Microbiology, 52(1), 66–72. https://doi.org/10.1139/w05-117
Smith, S. E., & Read, D. J. (2008).
Mycorrhizal symbiosis. Academic Press.
Spescha, A., Weibel, J., Wyser, L., Brunner, M., Hess Hermida, M., Moix, A., Scheibler, F., Guyer, A., Campos-Herrera, R., Grabenweger, G., & Maurhofer, M. (2023). Combining entomopathogenic Pseudomonas bacteria, nematodes and fungi for biological control of a below-ground insect pest. Agriculture, Ecosystems & Environment, 348, 108414.
Ye S, Yan R, Li X, Lin Y, Yang Z, Ma Y and Ding Z (2022) Biocontrol potential of Pseudomonas rhodesiae GC-7 against the root-knot nematode Meloidogyne graminicola through both antagonistic effects and induced plant resistance. Front. Microbiol. 13:1025727. doi: 10.3389/fmicb.2022.1025727
The Mechanics of Soil Fertility: Use of Sugar in Field Crops
Jolee Derrick, Precision Nutrient Management Ph. D. Student
Grace Williams, Soil Microbiology Ph. D. Candidate
Brian Arnall, Precision Nutrient Management Specialist
Recently, there has been increased interest in adding sugar to spray tank mixes, whether for post-emergence weed control or foliar nutrient applications. While there is limited work on impact of sugar inclusion in herbicide applications, some papers have posed potential enhancement (Devine and Hall, 1990). But since this is coming from a soil science group, we will only focus on soil impact. Following up the last blog, unlike humic substances, which represent more complex and relatively stable carbon forms, sugar is a highly labile carbon source. This rapid utilization of simple carbon sources is well documented to stimulate microbial activity and growth (Kuzyakov and Blagodatskaya, 2015). The general idea of utilizing sugar applications is that sugar has the capacity to improve spray performance, stimulate biological activity, increase organic matter mineralization, and ultimately result in improved yields.
Sugar additions can influence soil processes differently depending on system conditions. In systems with higher residual nitrogen and organic matter, responses may differ from those observed in Oklahoma production environments, where soils are typically lower in organic matter and microbial activity can occur for much of the year. Understanding how sugar functions in these systems requires a basic discussion of carbon dynamics. Sugar itself is almost entirely carbon and is readily consumed by microbes. It’s a simple molecule, which allows it to dissolve easily in water and be quickly utilized in the soil system. Crop residues, like wheat straw, are also carbon-rich but much more complex. They contain cellulose, hemicellulose, and lignin which are long carbon chains that take time to break down because microbes need specialized enzymes to access them.
For the sake of simplicity, we can group carbon into two key pools: labile carbon and particulate organic matter (POM). Labile carbon includes easily decomposed materials, which include the previously mentioned simple sugars that microbes can metabolize rapidly. These pools differ in turnover time and microbial accessibility, with labile carbon driving short-term microbial responses (Cotrufo et al. 2013). POM breaks down more slowly and serves as a longer-term nitrogen source through residue breakdown.
Soil microorganisms require both carbon and nitrogen to grow and maintain biomass, typically at a ratio of approximately 24 parts carbon to 1 part nitrogen. When readily available carbon is abundant, but nitrogen is limited, microbes increase their nitrogen demand and begin scavenging nitrogen from the surrounding soil. This process, better known as nitrogen immobilization, temporarily reduces nitrogen availability to crops. Additions of readily available carbon sources have consistently been shown to increase microbial nitrogen immobilization in soil systems (Recous et al. 1990).
In systems where sufficient nitrogen is present, microbial populations can expand rapidly. Fast-growing microbial species may dominate, continuing to immobilize nitrogen within their biomass. Eventually, when nitrogen becomes limiting, microbial populations decline to levels the system can support. This boom-and-bust cycle can disrupt nitrogen availability during critical stages of crop growth. These rapid shifts in microbial population and activity following carbon inputs are commonly observed in soil systems receiving easily decomposable substrates (Blagodatskaya and Kuzyakov, 2008).
This dynamic becomes especially relevant when considering residue management practices common in Oklahoma. Under no-till or limited-tillage systems, the crop residues have wide carbon-to-nitrogen (C:N) ratios, creating conditions where nitrogen immobilization can occur during the growing season.
Table 1 provides approximate C:N ratios for several crops commonly grown in Oklahoma. When additional carbon is introduced into these systems without accompanying nitrogen, the likelihood of microbial immobilization increases. While immobilization is not bad, it does create a question mark as Oklahoma’s variable climate means the following release of nutrients will be unpredictable.
Table 1. Table depicting the range of C:N ratios for residues of commonly utilized crops in Oklahoma. Ratios were obtained from Brady, N. C., & Weil, R. R. (2017). The Nature and Properties of Soils (15th ed.)
Now consider conventional tillage systems. In Oklahoma, no-till systems typically contain 2 to 3 percent organic matter, which is relatively high given our climate and extended periods of microbial activity. Conventional tillage systems often fall between 0.75 and 2.25 percent organic matter. Because soil organic matter is approximately 58 percent carbon, this represents a substantial difference in the soil carbon pool.
Tillage can temporarily enhance microbial access to both previously mentioned carbon pools. When tillage exposes previously protected carbon, microbial activity increases rapidly. This initial flush can temporarily increase nitrogen mineralization as organic nitrogen is converted to plant-available forms. However, this phase is short-lived. As microbial populations expand, nitrogen demand increases, leading to immobilization and reduced nitrogen availability.
Hypothetically, increased microbial growth and activity would rapidly mineralize organic matter, trigger a surge in NO₃⁻, deplete soil organic matter, and as resources become limiting and the environment can no longer sustain elevated microbial populations, this boom would be followed by a population crash. This relationship is ultimately driven by the soil C:N ratio, which introduces an interesting additional complexity of residue. Different residues bring very different carbon-to-nitrogen balances into the system, and microbes respond accordingly. High carbon residues give microbes plenty of energy but very little nitrogen, so they pull N out of the soil to meet their needs. Residues with lower C:N ratios (soybean, alfalfa, etc.) do opposite, releasing nitrogen as they break down. Now the real question becomes where the critical point sits, and when does management push the system from the threshold of immobilization and mineralization.
These hypotheses form the foundation for new research currently underway through the Precision Nutrient Management Program. Initial proof-of-concept work has already been completed, providing a necessary steppingstone to address these questions.
Figure 1. Graph depicting the different concentrations of nitrate leached corresponding to applied treatments in the proof-of-concept work
The preliminary work (Figure 1) evaluated different sugar sources applied alongside a high-nitrogen product to assess the extent of nitrogen immobilization. Although these studies were conducted using potting soils, clear trends were apparent. Treatments containing sugar consistently showed greater nitrogen immobilization compared to treatments without sugar. This response is consistent with studies showing that additions of simple carbon substrates stimulate microbial growth and increase nitrogen immobilization (Dendooven et al. 2006). Building on this work, an active field-based research project is underway to evaluate how sugar additions influence nitrogen availability and microbial dynamics under real-world Oklahoma production conditions.
From an agronomic standpoint, sugar functions primarily as a readily available carbon source that stimulates microbial growth. In nitrogen-limited systems, this response increases the likelihood that nitrogen will be incorporated into microbial biomass rather than remaining immediately available for crop uptake.
Finally, we conclude with a conceptual consideration. If increased OM mineralization leads to greater plant biomass, this process may partially offset losses of OM. Greater biomass production could return more residues to the soil, contributing to the OM pool in the upper soil profile. Therefore, the system may compensate for OM mineralization through the rebuilding of organic matter via plant inputs. However, the stabilization of this carbon depends on microbial processing and physical protection within the soil matrix (Cotrufo et al. 2015)
However, while the underlying logic is sound, this concept has not been extensively studied within Oklahoma cropping systems. This blog does not address the impact of sugar applications on residue breakdown, and the potential impact of such. Future research through the Precision Nutrient Management Program will further investigate the mineralization process to better understand carbon dynamics within these systems.
Take Home:
- Oklahoma production systems generally have lower residual N and high carbon residues, creating conditions conducive to N immobilization
- Adding sugar increases microbial growth, creating population booms that will momentarily increase mineralization, but then immediately immobilize residual nitrogen.
- Tillage can amplify the negative effects of sugar by exposing more carbon and reducing soil organic matter
- Proof-of-concept work shows sugar triggered a net nitrogen immobilization in a carbon heavy environment
- Proof-of-concept work also suggests that when additional nitrogen is present, sugar additions may shift the system toward net mineralization rather than immobilization.
Work Cited:
Blagodatskaya, E., & Kuzyakov, Y. (2008). Mechanisms of real and apparent priming effects. Biology and Fertility of Soils, 45, 115–131.
Brady, N. C., and R. R. Weil. “The Nature and Properties of Soils, 15th Edn (eBook).” (2017).
Cotrufo, M. F., Wallenstein, M. D., Boot, C. M., Denef, K., & Paul, E. (2013). The Microbial Efficiency-Matrix Stabilization (MEMS) framework. Global Change Biology, 19, 988–995.
Cotrufo, M. F., Soong, J. L., Horton, A. J., Campbell, E. E., Haddix, M. L., Wall, D. H., & Parton, W. J. (2015). Formation of soil organic matter via biochemical and physical pathways of litter mass loss. Nature Geoscience, 8(10), 776–779.
Dendooven, L., Verhulst, N., Luna-Guido, M., & Ceballos-Ramírez, J. M. (2006). Dynamics of inorganic nitrogen in nitrate- and glucose-amended alkaline–saline soil. Plant and Soil, 283(1–2), 321–333.
Devine, M. D., & Hall, L. M. (1990). Implications of sucrose transport mechanisms for the translocation of herbicides. Weed Science, 38(3), 299–304.
Kuzyakov, Y., & Blagodatskaya, E. (2015). Microbial hotspots and hot moments in soil: Concept & review. Soil Biology and Biochemistry, 83, 184–199.
Recous, S., Mary, B., & Faurie, G. (1990). Microbial immobilization of ammonium and nitrate in cultivated soils. Soil Biology and Biochemistry, 22, 913–922.
Small Pest, Big Problems: Wheat Curl Mites and Wheat Streak Mosaic Virus Detected in Oklahoma
Ashleigh Faris, Cropping Systems Entomologist, IPM Coordinator
Meriem Aoun, Wheat Pathologist
Department of Entomology & Plant Pathology,
Oklahoma State University
Wheat Curl Mite (WCM) activity has been confirmed in Washita County, located in western Oklahoma. While the mites themselves are difficult to see, they can have a considerable impact on wheat health, primarily due to their role as vectors for several viral diseases such as wheat streak mosaic virus (WSMV). The Plant Disease and Insect Diagnostic Laboratory (PDIDL) has confirmed WSMV in the sample where WCM were detected in Washita County. This week, the PDIDL has also confirmed infection by WSMV in Blaine County (Canton, OK), McCurtain County (Garvin, OK), and Cleveland County (Noble, OK).
Identification
The Wheat Curl Mite is nearly invisible to the naked eye. At approximately 1/100 of an inch long, these pests require a 10x – 20x hand lens for proper identification.
- Appearance: They are white or cream-colored, cigar-shaped (cylindrical), and possess only four legs located near the head (Figure 1).
- Behavior: They are typically found in the protected areas of the plant, such as developing, youngest leaves or the furrows of the leaf surface. As the leaf unfurls, the mites migrate to the next emerging leaf.
Figure 1. Wheat curl mites and eggs on a wheat leaf (A, B), and mites on a maturing wheat kernel (C). Images courtesy G. Bauchan and R. Ochoa, USDA-ARS.
Biology and Life Cycle
Understanding the WCM life cycle is critical for preventative management:
- Rapid Reproduction: Under optimal temperatures (75° – 85°F), a WCM can complete its life cycle in 7 to 10 days. This allows populations to explode rapidly during warm autumns or springs.
- Dispersal: WCMs cannot fly; they rely entirely on wind currents to move from plant to plant or field to field. They crawl to the tips of leaves and hitchhike on the wind.
- Survival (The Green Bridge): WCMs are obligate parasites, meaning they require living green tissue to survive and reproduce. They persist through the summer on volunteer wheat and various perennial or annual grasses. This is known as the green bridge. If this bridge is not broken, mites move into the newly planted crop in the fall.
Damage and Virus Transmission
WCMs cause two types of damage:
- Direct Feeding: Mites suck sap from the leaf cells. This causes the edges of the leaf to roll inward (the curl part of WCM) (Figure 2). This curling provides a protected microclimate for the mites to reproduce. Heavy infestations can cause stunting and a slowed appearance in growth.
- Viral Vector (Primary Concern): The WCM is the sole vector for Wheat Streak Mosaic Virus (WSMV), High Plains Wheat Mosaic Virus (HPWMoV), and Triticum Mosaic Virus (TriMV).
- Symptoms: Infected plants show yellowing, mottled or streaked leaves, and severe stunting (Figures 3 & 4).
- Impact: If infection occurs in the fall, yield loss can be up to 100%. Spring infections are generally less damaging.
Scouting Techniques
Because the mites are so small, scouting focuses on leaf symptoms and having a hand lens:
- Check your Fields: Examine the youngest leaves of the wheat plant. Look for the characteristic inward rolling of the leaf edges (Figure 2).
- Use Magnification: Slowly unroll a suspect leaf and use a hand lens to look for tiny, white, slow-moving specks in the leaf furrows.
- Pattern of Infestation: Wind-dispersed mite infestations often start at the edge of a field (particularly edges adjacent to volunteer wheat or CRP land) and move inward in the direction of prevailing winds. Areas with infestations may show signs of yellowing and appear as patches distributed at random across the field (Figure 4).
Figure 2. Infestation of wheat curl mites on wheat results in tightly curled leaves and entrapment of subsequent leaves within the curl (A). After full leaf emergence, a tight curl at the leaf edge remains (B). Images courtesy of UNL Extension.
Figure 3. Wheat streak mosaic virus (WSMV) symptoms includeyellowing, mottled or streaked leaves. Image courtesy of Meriem Aoun, Oklahoma State University.
Figure 4. Plants at field margins, neighboring a wheat curl mite source, are the first to become infected with viruses of the Wheat Streak Mosaic Virus (WSMV) complex and develop symptoms, such as yellowing and streaking. Notice the gradient in color from the field edge (left) toward the center of the wheat field. Image courtesy of UNL Extension.
Management Recommendations
Currently, there are no effective rescue chemical treatments for WCM once symptoms appear in the field. Miticides generally do not reach the mites hidden inside the curled leaves. Management must be proactive:
- Manage volunteer wheat and grassy weeds: This is the most effective management tool to break the green bridge. Ensure all volunteer wheat and grassy weeds are completely dead (via tillage or herbicide) at least two weeks prior to planting the new crop. WCMs will starve within days without a living host.
- Delayed Planting: Planting wheat later in the fall reduces the window of time that mites must migrate into the crop and slows their reproduction rate as temperatures drop.
- Variety Selection: Some wheat varieties offer resistance or tolerance to WCM or WSMV. Consult the latest OSU variety trial data to select adapted varieties for north-central Oklahoma that carry these traits. Currently, Breakthrough is the most resistant OSU variety, which carries the WSMV resistance gene, Wsm1.
Brown Wheat Mite Activity in North Central Oklahoma
Ashleigh Faris, Cropping Systems Entomologist, IPM Coordinator
Department of Entomology & Plant Pathology,
Oklahoma State University
Following a period of dry weather, wheat growers in central Oklahoma are reporting activity of the Brown Wheat Mite (BWM). Unlike many other wheat pests, BWM thrives in drought conditions, and its damage can often be mistaken for moisture stress or nutrient deficiency.
Identification
The Brown Wheat Mite is small—about the size of a needle point—but is generally easier to spot than the Wheat Curl Mite because it is active on the leaf surface.
- Appearance: BWM has a dark red to brownish-black, oval-shaped body (Figure 1).
- Distinguishing Feature: Its front legs are significantly longer than its other three pairs of legs.
- Behavior: They are most active during the day, particularly in the afternoon, and will quickly drop to the ground if the plant is disturbed (Figure 2).
Figure 1. Brown wheat mite (BWM).
Figure 2. Brown wheat mites (BWM) on wheat. Image courtesy L. Galvin, OSU Extension.
Biology and Life Cycle
BWM populations consist entirely of females that produce offspring without mating (parthenogenesis), allowing for extremely rapid population growth under dry conditions. The BWM has a unique life cycle in that it can lay two types of eggs. Environmental conditions dictate when these two types of eggs are laid:
- Red Eggs: Laid during the growing season and hatch in about a week when conditions are favorable.
- White (Diapause) Eggs: Laid as temperatures rise and the crop matures. They are highly resistant and allow the population to survive the summer heat, hatching only when cooler, wetter weather arrives in the fall.
Damage
BWM damage is caused by the mites piercing plant cells and sucking out the plant nutrients.
- Symptoms: Initial damage appears as “stippling” (fine white or yellow spots) on the leaves. As feeding continues, leaves take on a silvery or bronzed appearance (Figure 3).
- Tipping: Heavy infestations cause the tips of the leaves to turn brown and die.
- Weather Interaction: Damage is most severe when plants are already under drought stress. Because both BWM damage and drought cause yellowing/browning, it is essential to confirm the presence of mites before treating.
Figure 3. Brown wheat mite (BWM) damage.
Scouting
Because BWM is highly mobile and drops when disturbed, careful scouting is required:
- Timing: Scout during the warmest part of the day when mites are most active on the upper leaves.
- The Paper Test: Gently but quickly shake or tap wheat plants over a white piece of paper or a white clipboard. Look for tiny dark specks moving across the surface.
- Economic Threshold: While thresholds vary based on crop value and moisture stress, research suggests a treatment threshold of 25 to 50 brown wheat mites per leaf in wheat that is 6 inches to 9 inches tall is economically warranted. An alternative estimation is “several hundred” per foot of row. If the wheat is severely stressed, the lower end of that threshold should be used.
Management Recommendations
- The “Rain” Factor: A significant, driving rain is often the most effective control for BWM. Rain can physically knock mites from the plant and promote fungal pathogens that naturally reduce the population.
- Chemical Control: If populations exceed the threshold and no rain is in the forecast, chemical intervention may be necessary. Know the cost of the treatment and value of your wheat so you can determine if an application is a worth return on investment.
- Effective Ingredients: Organophosphates (such as Dimethoate) have historically provided better control than many pyrethroids, as the latter can sometimes result in mite “flaring” or simply fail to provide adequate residual control.
- Coverage: High water volume is critical to ensure the insecticide reaches the mites, especially if they have moved toward the base of the plant.
- Pre-harvest Intervals & Grazing Restrictions: Always read and follow the label guidelines. For more on acaricides that can be applied in wheat see the Oklahoma State University Fact Sheet “Management of Insect and Mite Pests in Small Grains” (CR-7194).
- Cultural Practices: Since BWM thrives in dry, dusty conditions, maintaining good soil moisture and vigorous plant growth can help the crop tolerate feeding. Here’s to hoping for some rain soon in the forecast; we could really use it for lots of reasons in Oklahoma.
Corn Hybrids’ Yield Response to Limited Well Capacities in the Central High Plains
Macie McPeak: M.S in Irrigation and Water Management
Sumit Sharma : Extension Specialist for High Plains Irrigation and Water Management
Background
The Central High Plains, which include the Oklahoma Panhandle, Southwest Kansas, Southeast Colorado, and Northern Texas Panhandle, is a heavily farmed semi-arid region that depends on the Ogallala Aquifer for irrigation to ensure stable crop yields. However, the continuous decline of the Ogallala Aquifer has resulted in increased need for irrigation strategies that conserve water while maintaining crop profitability. Corn remains the most water consuming crop with highest productivity per unit of irrigation applied, and strong economic returns in the Central High Plains region. However, corn is also the most sensitive to water stress among all the existing cropping systems (including sorghum, cotton, and sunflower, soybeans and wheat). Declining water table has reduced the well capacities in many areas in the region, which cannot meet crop water demand, making it a growing challenge for corn production. Therefore, there is a need for research in irrigation strategies and agronomic choices such as drought tolerant hybrids, seeding rate, planting date, and hybrid maturity for sustainable and profitable corn production with reduced well capacities in the region. This blog discusses the yield response of different corn hybrids to limited well capacities in the Oklahoma Panhandle area of the Central High Plains.
Limited well capacities only meet partial crop water demand, which in general leads to yield declines especially in high water demanding crops such as corn. Several previous studies suggest that crop productivity does not significantly decrease as long as irrigation is maintained at approximately 75–80% of full evapotranspiration (ET) replacement (Su et al., 2022; Klocke et al., 2007; Zhao et al., 2019). However, when irrigation levels are more restricted, such as under reduced well capacities, there can be substantial yield losses and diminished economic returns. The magnitude of yield reduction varies with region, hybrids, and growth stage at which water stress occurred. For example, in the Central High Plains the corn ET demand is highest in Texas Panhandle and decreases as we move north towards Nebraska. Zhao et al. (2019) found that applying 75% ET in the Texas Panhandle produced corn yields equivalent to full irrigation, whereas reducing irrigation to 50% caused significant yield reductions. Similarly, Klocke et al. (2007) reported that limited irrigation at roughly 50% of full ET replacement in Nebraska achieved 80–90% of fully irrigated yields across multiple crop rotations. Therefore, the irrigation strategies which work in one region may not work the same way in other regions with different crop water demand and must be tested for the region-specific climatic conditions.
The current study was conducted in 2025 at the Oklahoma Panhandle Research and Extension Center in Goodwell, OK. Four Pioneer brand corn hybrids including P13777 (113 day maturity), P10625 (110 day maturity), P05810 (105 day maturity), and P14346 (114 days maturity) were planted at 22,000 and 28,000 seeds per acre. The hybrids were irrigated with a center pivot fitted with variable rate irrigation system at 200, 300, 400, and 500 GPM well capacities. The well capacities were simulated by adjusting the frequency of irrigation events.
Results & Discussion
The crop received 12.1 inches of rain from planting until physiological maturity, while total rainfall from April till September was over 15 inches. Manual probing of the field showed near 4 feet soil profile at the time of planting which can hold up to 2 inches of plant available water per foot. The well capacities 200, 300, 400, and 500 GPM treatments received 7.4, 8.9, 10.8, and 12.0 inches of irrigation, respectively. The data showed no significant effect of population on corn yield across hybrids for any well capacity. However, the hybrids showed significant interaction with well capacities, which indicated that hybrid yield response varied at different capacities (Figure 1). In general, the average yield declined from longest maturity to shortest maturity hybrids irrespective of the well capacity, but was only statistically significant at for 200 GPM (Figure1). At this irrigation level, the shortest maturity hybrid P05081 yielded significantly lower yield than longest maturity hybrid P14364, while P13777 and P10625 were not different from either of these two hybrids.
Although there was no statistical difference among the hybrids at 500, 400, and 300 GPM, when compared across well capacities, yield reductions were most pronounced at the 200 and 300 GPM irrigation levels for each individual hybrid, indicating that irrigation capacity was the primary yield limiting factor under restricted water availability (Figure 2). While the exact causes of this abrupt decline are not yet understood, as mentioned in the beginning of this blog, previous literature has suggested that severe yield decline in corn can be expected when irrigation is reduced to 60% ET replacement in the study region. Both 300 and 200 GPM well capacities met 60 and 65% crop ET demand, while 400 and 500 GPM met 71 and75% crop ET demand, respectively. More data will be needed to ascertain these threshold levels of well capacities for corn production in this region.
All the hybrids showed a positive yield response to Irrigation+Rain with different yield gains per inch of water applied (Figure 3). Hybrid P10625 registered highest yield gain of 14.1 bushel per inch of water applied, followed by P13777 (12.0 bu), P05081 (11.9 bu), and P14364 (11.6 bu). The stronger coefficient of regression (>80%) for two short maturity varieties indicated that irrigation was stronger yield limitation factor for these hybrids, in comparison to 114 and 113-day maturity hybrids for irrigation explained on 67 and 69% variability, respectively. This suggests that besides irrigation there might be other factors which could contribute to filling the yield gaps for given irrigation levels in longer maturity hybrids.
Planting population did not significantly affect grain yield across irrigation capacities. When pooled across the hybrids for individual planting populations, 28,000 seeding rates resulted in gain of 0.1, 2.6, 5, and 12 bushels per acre for 200, 300, 400, and 500 GPM, respectively. This indicates that higher planting populations at well capacities of 400 or above should be considered, while reducing population at 300 GPM or lower might be more cost-effective option.
Take Home
- Irrigation capacity remains the primary determinant of yield potential under limited well capacities in the Central High Plains.
- Pre-irrigation and recharging the soil profiles will be critical to support crop water demand for limited well capacities.
- Short maturity hybrids appeared to have consistently lower average yield and more vulnerable for yield losses at limited irrigation. However, one must consider that the growing conditions were more conducive for corn production in 2025 which generally favor long maturity hybrids. Therefore, long-term data will be required to assess the performance of short maturity hybrids during inclement growing seasons.
- Even though population didn’t significantly influence the grain yield. The 28,000 seeding rates overall had higher average yield at 400 and 500 GPM. Therefore, producers should consider the higher population at these well capacities or more.
- Overall, irrigation is the most important factor for yields, but there is a need for long-term agronomic data on hybrid maturity and population along with economic analysis to ascertain these findings.
Thoughts from an Agronomist- 1 Management of the Primordia
Josh Lofton, Cropping Systems Specialist
Many crop management recommendations emphasize actions that must be taken well before a crop reaches what we often call “critical growth stages.” Management this early can seem counterintuitive when the crop still looks small, healthy, or unchanged aboveground. However, much of a crop’s yield potential is determined early in the season at a level we cannot see in the field. Long before flowers, tassels, or heads (or any reproductive structure) appear, the plant is already making developmental decisions that shape its final yield potential. Understanding this “behind the scenes” process helps explain why timely, early-season management is often more effective than trying to correct problems later.
At the center of this process is the shoot apical meristem, commonly referred to as the growing point. This tissue produces leaf and reproductive primordia, which are the earliest developmental stages of future everything in the plant. These primordia form well before the corresponding plant parts are visible. Once these structures initiate—or if they fail to begin due to stress—the outcome is permanent. The plant cannot later in the season go back and recreate leaf number, leaf size, or reproductive capacity. As a result, early environmental conditions and management decisions play a disproportionate role in determining yield potential.
Corn is a good example of how early development influences final yield. By the time corn reaches the V4 growth stage, the plant only has four visible leaves with collars, yet internally it is far more advanced. Most of the total leaf primordia that will eventually form the full canopy have already begun, and the potential size of the ear is starting to be established. During this stage, the growing point is still below the soil surface and somewhat protected from some stressors but highly susceptible to others. Nitrogen deficiency, cold temperatures, moisture stress, compaction, or herbicide injury at or before V4 can reduce leaf number and limit leaf expansion. Even if growing conditions improve later, the plant cannot replace leaf primordia that were never formed, which reduces its ability to intercept sunlight and support high yields.
As corn approaches tasseling (VT), the crop enters a stage that is visually and physiologically important. Pollination, fertilization, and early kernel development occur at this time, and stress can have a critical impact on kernel set. However, by VT, the plant has already completed leaf formation, and much of the ear size potential has already been determined several growth stages earlier. Management at VT is therefore focused on protecting yield rather than creating it. Late-season nutrient applications may improve plant appearance or maintain green leaf area, but they cannot increase leaf number or rebuild ear potential lost due to early-season stress. This distinction helps explain why some late inputs show limited yield response even when the crop looks responsive.
Grain sorghum provides another clear example of why early management is emphasized. Although sorghum often grows slowly early in the season and may appear unimportant during the first few weeks after emergence, the first 30 days are among the most critical periods in its development. During this time, the growing point is actively producing leaf primordia and transitioning from vegetative growth toward reproductive development. Head size potential is primarily established during this early window, and the plant’s capacity to support tillers is influenced by early nutrient availability and moisture conditions. Stress from nitrogen deficiency, drought, weed competition, or restricted rooting during the first 30 days can reduce head size and kernel number long before visible symptoms appear.
Once sorghum reaches later vegetative and reproductive stages, much like corn at VT, management shifts from building yield potential to protecting what has already been determined. Improving conditions later in the season can help maintain plant health and grain fill, but it cannot fully compensate for early limitations imposed at the primordial level. This is why early fertility placement, timely weed control, and moisture conservation are consistently emphasized in sorghum production systems.
Across crops, a typical pattern emerges: the growth stages we observe in the field often reflect decisions the plant made weeks earlier. When agronomists stress early-season management, they are responding to plant biology rather than simply following tradition. By the time visible “critical stages” arrive, the plant has already established many of the components that define yield potential.
The key takeaway is that effective crop management must be proactive rather than reactive. Early-season decisions support the crop while it is still determining how many leaves it can produce, how large its reproductive structures can become, and how much yield it can ultimately support. Waiting until stress becomes visible often means responding after the plant has already adjusted its potential downward. Recognizing what is happening at the primordial level helps explain why management ahead of critical stages consistently delivers the greatest return, even when the crop appears small and unaffected aboveground.
For questions or comments reach out to Dr. Josh Lofton
josh.lofton@okstate.edu
Using soil moisture trend values from moisture sensors for irrigation decisions
Sumit Sharma, Extension Specialist for High Plains Irrigation and Water Management
Kevin Wagner, Director, Oklahoma Water Resources Center
Sumon Datta, Irrigation Engineer, BAE.
Sensor based and data driven irrigation scheduling has gained interest in irrigated agriculture around the world, especially in semi-arid areas because of the easy availability of commercial irrigation scheduler technology such as soil moisture sensors and crop models. Moisture sensing has particularly gained interest among the agriculture community due to ease of availability of the sensors to the producers, affordable costs, and easy to use graphical user interface. Economic potential of sensors in saving irrigation costs, data interpretation training through extension education programs, and policy initiatives have also helped with adoption of the sensors, especially in the United States. However, sensor adoption and efficient use can still be challenging due to poor data interpretation, steep learning curves, overly high expectations and subscription costs. This blog briefly discusses scenarios where sensors can be helpful in irrigated agriculture. For moisture sensor types, functioning and installation, readers are referred to BAE-1543 OSU extension factsheet.
Irrigation Scheduling
Irrigation scheduling with soil moisture sensors follows traditional principles of field capacity (FC), plant available water, maximum allowable depletion (MAD), and permanent wilting point (PWP). Figure 1 shows the transition of soil moisture level from field capacity to MAD, and to permanent wilting point in a typical soil. The maximum amount of water that a soil can hold after draining the excess moisture is called field capacity. At this point, all the water in soil is available to the plants. As the moisture content in the soil declines, it becomes more difficult for the plants to extract moisture from the soil. The soil moisture level below which the available moisture in soil cannot meet the plant’s water requirement is called the MAD. The water stress that occurs once moisture level goes below this moisture level can cause yield reductions in crops. Therefore, irrigation should be triggered as soon as the soil moisture level approaches this point (MAD) to avoid any yield losses (for detailed information on MAD, its value for different soils and crops, and irrigation scheduling, readers are referred to BAE-1537). Modern soil moisture sensors can come self-calibrated and are equipped with water stress threshold levels for different crops to avoid water stress or overwatering (Figure 2). These decisions are useful in furrow and drip irrigation systems where irrigation triggers can be synchronized with MAD values.
Figure 2: Screenshots of graphic user interface of three sensors a) GroGuru b) Sentek c) Aquaspy (Top to bottom) with threshold levels for soil moisture conditions. Aquspy and Sentek credits: Sumit Sharma. GroGuru image credits: groguru.com
Soil Moisture Trends and Irrigation Depths
Soil moisture sensors can help make data-informed decisions about scheduling irrigation. Previous studies have shown that the moisture values may vary from one sensor to the other and may not represent the exact moisture levels in soil. However, all soil moisture sensors exhibit trends in recharge and decline in soil moisture conditions. These real time soil moisture trends can be used to make informed decisions to adjust irrigation and improve water use efficiency. In high ET demand environments of Oklahoma, pivots are usually not turned off during the peak growing season, yet sensors can help in making decisions for early as well as late growing periods.
One of the easiest adjustments that could be made using soil moisture sensor data is the adjustment of irrigation depth. In an ideal situation, every irrigation event should recharge the soil profile to field capacity; however, this is often limited by the crops’ water demand and the well/irrigation capacity to replenish soil moisture levels. Each peak in soil moisture detected by sensors shows irrigation or rain, which ideally should be bringing moisture to same level after irrigation. However, reduction in moisture peaks in the soil moisture profile with every irrigation often indicates greater crop water demand than what is replenished with irrigation. In such scenarios, as allowed by capacity and infiltration rates, the irrigation depth can be increased. These trend values are particularly useful for center pivot irrigation systems, where triggering irrigation based on MAD might lag due to time and space bound rotations of the pivots in Oklahoma weather conditions.
Figure 3: A screenshot from Aquaspy agspy moisture sensor showing moisture at 8” (blue) and 28” (red) with each irrigation event. Data and image credit: Sumit Sharma
Last irrigation can be a tricky decision to end the cropping season. For summer crops, this is the time when crop ET demand is declining due to decline in green biomass and cooler weather patterns. Similar moisture trends can be used to make decisions for the last irrigation events, which can be skipped or reduced if the profile moisture is good, or can be provided if profile moisture is low. This is important because in an ideal situation, one would want to end the season with a relatively drier profile to capture and store off-season rains. Additionally, saving water on last irrigation can save operational cost and potentially cover the cost of moisture sensor subscriptions.
These decisions can be illustrated with Figure 3, which shows the trends of declining and recharging in a soil profile under corn at 8- and 28-inch depth. This field was irrigated with a center pivot irrigation system which was putting 1-1.25 inches of water with each irrigation event; however, the peak water recharge rate at both depths was declining with each irrigation. This coincided with peak growth period indicating rising ET demand of the crop than what was replenished by the irrigation. Later, two rain events, in addition to irrigation, replenished soil moisture in both layers. As the pivot was already running at a slow speed, slowing it further was not an option without triggering runoff for this soil type and this well capacity. Further in the season, when the crop started to senesce and ET demand declined, each irrigation event added to the moisture level of the soil. This allowed the producer to shut down the pivot between 70% starch line and physiological maturity for the crop to sustain at a relatively wet soil profile and leave the soil in relatively drier profile for the off-season.
In high ET demanding conditions of Western Oklahoma, crops often rely on moisture stored in deep soil profiles during the peak ET period when well capacities can’t keep up with crop water demand. In the high ET demanding environments of Oklahoma, irrigated agriculture depends heavily on profile moisture storage. Declining soil profile moisture is common during peak ET periods in high water demanding crops such as corn. These observations are useful if one starts the season with considerable moisture in the soil profile, however such trends may be absent if the season is started with a dry soil profile. Dry soil profiles can be recharged early in the season with pre-irrigation or deeper early irrigations (if allowed by the infiltration rate of the soil), when crop ET demand is low, to build the soil moisture profile. As such, sensors can be used in reducing the irrigation depth or skipping irrigation in early cropping systems if one starts with a full profile. This usually allows root growth through the profile to chase the moisture in deeper layers. It should be noted that the roots will grow and chase moisture only if there is a wet profile, and not through a dry soil profile.
Sensor installation and calibration are important for efficient use of these devices in irrigation decision making. Poor installation can often lead to poor data and wrong decision making. Although modern sensors are self/factory calibrated, some do provide the option to adjust threshold levels manually based on field observations. Early installation of sensors can be useful in making informed decisions as soon as the season starts. For a more detailed analysis of proper sensor installation, refer to BAE-1543. Producers are encouraged to integrate other means of irrigation planning with soil moisture sensing, such as a push rob to probe the soil profile or OSU Mesonet’s irrigation planner to further validate the sensor data. Further, the cliente should consider their irrigation capacities before investing in soil moisture sensors, as sensors may always show a deficit in low well capacities which cannot meet crop’s water demand.
References:
Taghvaeian, S., D. Porter, J. Aguilar. 20221. Soil moisture-sensing systems for improving irrigation scheduling. BAE-1543. Oklahoma State Cooperative Extension. Available at: https://extension.okstate.edu/fact-sheets/soil-moisture-sensing-systems-for-improving-irrigation-scheduling.html
Datta, S., S. Taghvaeian, J. Stivers. Understanding soil water content and thresholds for irrigation management. BAE-1537. Oklahoma State Cooperative Extension. Available at: https://extension.okstate.edu/fact-sheets/understanding-soil-water-content-and-thresholds-for-irrigation-management.html
For more information please contact Sumit Sharma sumit.sharma@okstate.edu
Toto, I’ve a feeling we’re not in Kansas anymore. Double Cropping, Orange edition
It has been pointed out that the blog https://osunpk.com/2025/06/09/double-crop-options-after-wheat-ksu-edition/ had a significant Purple Haze. And I should have added the Oklahoma caveat. So Dr. Lofton has provided his take on DC corn in Oklahoma.
Double-crop Corn: An Oklahoma Perspective.
Dr. Josh Lofton, Cropping Systems Specialist.
Several weeks ago, a blog was published discussing double-crop options with a specific focus on Kansas. I wanted to address one part of that blog with a greater focus on Oklahoma, and that section would be the viability of double-crop corn as an option.
Double-crop farming is considered a high-risk, high-reward system to try. Establishing a crop during the hottest and often driest parts of summer can present challenges that need to be overcome. Double-crop corn faces these same challenges and, in some seasons, even more. However, it is definitely a system that can work in Oklahoma, especially farther south. If you look at that original blog post, one of the main challenges discussed is having enough heat units before the first frost. When examining historic data, like those below from NOAA, the first potential frost date for Northcentral and Northwest Oklahoma may be as early as the first 15 days of October but more often will be in the last 15 days of October. In Southwest and Central Oklahoma, this date shifts even later to the first 15 days of November. This is later than Kansas, especially northern Kansas, which has a much higher chance of experiencing an early October freeze. I do not want to downplay this risk; however, it is one of the biggest risks growers face with this system, and a later fall freeze would greatly benefit it. We have been conducting trials near Stillwater for the past five years on double-crop corn and have only failed the crop once due to an early freeze event. But in that year, both double-crop soybean and sorghum also did not perform well.
The main advantage of double-crop corn is that if you miss the early season window, it offers the best chance for the crop to reach pollination and early grain fill without the stress of the hottest and driest part of the year. Therefore, careful management is crucial to ensure this benefit isn’t lost. In Oklahoma, we have two systems that can support double-crop corn. In more central and southwest Oklahoma, especially under irrigation, farmers can plant corn soon after wheat harvest, similar to other double-crop systems. This planting window helps minimize the impact of Southern Rust, which can significantly reduce yields in some years, and may reduce the need for extensive management. This earlier planting window is often supported by irrigation, enabling the crop to endure the hotter, drier late July and early August periods. Conversely, in northern Oklahoma, planting often occurs in July to allow pollination and grain fill (usually 30-45 days after emergence) to happen in late August and early September. During this period, the chances of rainfall and cooler nighttime temperatures increase, both of which are critical for successful corn production.
Other management considerations include maturity. Based on initial testing in Oklahoma, particularly in the northern areas, we prefer to plant longer-maturity corn. Early corn varieties have a better chance of maturing before a potential early freeze but also carry a higher risk of undergoing critical reproduction stages (pollination and early grain fill) during hot, dry periods in late summer. Testing indicates that corn with a maturity of over 110 days often works well for this. However, this does not mean growers cannot plant shorter-season corn, especially if the season has generally been cooler, though the risk still exists depending on how quickly the crop can grow. Based on testing within the state, the dryland double-crop corn system typically does not require adjustments to other management practices, such as seeding rates or nitrogen application. Because of the need to coordinate leaf architecture and manage limited water resources, higher seeding rates are not recommended. Maintaining current nitrogen levels allows the crop to develop a full canopy.
The final question often comes as; how does it yield? This will depend greatly. Corn looks very good this year across that state, especially what was able to be planted earlier in the spring. However, in recent years, delaying even a couple of weeks beyond traditional planting windows has lowered yields enough that double-crop yields are often similar. We have often harvested between 50-120 bushels per acre in our plots around Stillwater with double-crop systems. So, the yield potential is still there.
In the end, Oklahoma growers know that double-crop is a risk regardless of the crop chosen. There are additional risks for double-crop corn, such as Southern Rust in the south and freeze dates in the north. This risk is increased by the presence of Corn Leaf Aphid and Corn Stunt last season, and it is not clear if these will be ongoing problems. Therefore, growers need to be careful not to expect too much or to invest too heavily in inputs that may not be recoverable if there is a loss. One silver lining is that if double-crop corn doesn’t succeed in any given year, growers can still use it as forage and recover at least some of their costs.
Any questions or concerns reach out to Dr. Lofton: josh.lofton@okstate.edu
Meet the Aster Leafhopper and Learn How to Distinguish it from the Corn Leafhopper
Ashleigh M. Faris: Extension Cropping Systems Entomologist, IPM Coordinator
Release Date June 3 2025
Last year’s corn stunt disease outbreak, caused by the corn leafhopper transmitting pathogens associated with corn stunt disease, has been on everyone’s minds. Over the past few weeks, I’ve received several calls from growers, crop consultants, and industry partners concerned about leafhoppers in corn. Fortunately, none have been corn leafhoppers, the vast majority have instead been aster leafhoppers. So far, no corn leafhoppers have been reported north of central Texas. Oklahoma did not have any reports of overwintering corn leafhoppers so if we have the insect this year it will need to migrate northward from where it currently resides. For a refresher on the corn leafhopper and corn stunt disease, check out these two previously posted OSU Pest e-Alerts: EPP-25-3and EPP-23-17.
Leafhoppers in general are insects that we have had for many years in our row and field crops. But we likely did not pay attention to them or notice them until this past year due to our heightened awareness of their existence thanks to the corn leafhopper and corn stunt disease. Below is guidance on how to distinguish between the corn leafhopper and aster leafhopper. Remember, if the corn leafhopper is detected in the state, OSU Extension will notify growers, consultants, and industry partners through Pest e-Alerts and our social media channels.
Aster Leafhopper Overview
The aster leafhopper (aka six spotted leafhopper), Macrosteles quadrilineatus, is native to North America and can be found in every U.S. state, as well as Canada. This polyphagous insect feeds on over 300 host plant species including weeds, vegetables, and cereals. Like many other leafhoppers, the aster leafhopper can be a vector of pathogens that cause disease, but corn stunt is not one of them. Instead, aster leafhoppers cause problems in traditional vegetable growing operations, as well as floral production. There is currently no concern for this insect being a vector of disease in row or field crops, including corn. Check out the OSU Pest a-Alert EPP-23-1to learn more about this insect and aster yellows disease.
Aster Leafhopper versus Corn Leafhopper
The corn leafhopper (Photo 1A) and the aster leafhopper, as well as many other leafhopper species have two black dots located between the eyes of the insect (Photo 1). Aster leafhopper adults are 0.125 inches (3 mm) long, with transparent wings that bear strong veins, and darkly colored abdomens (Photo 1B). Their dark abdomen can cause the aster leafhopper to appear grey when you see them in the field. Their long wings can also make the insect appear to have a similar appearance to the corn leafhopper (Dalbulus maidis) (Photo 1).
Characteristics that differentiate the corn leafhopper from the aster leafhopper are as follows. When viewed from above (dorsally): 1) the corn leafhopper’s dots between the eyes have a white halo around them and the aster leafhopper’s dots between eyes lack the white halo and 2) the corn leafhopper has lighter/finer wing veination than the aster leafhopper (Photo 1). When when viewed from their underside (ventrally) 3) the corn leafhopper lacks markings on their face whereas the aster leafhopper has lines/spot on the face and 4) the abdomen of the corn leafhopper lacks the dark coloration of the aster leafhopper (Photo 2).
Confirming Corn Leafhopper Identification
It is important to note that many insects will have their cuticle darken as they age. This, along with there being light and dark morphs of many insects can lend to additional confusion when distinguishing one species from another. If you believe that you have a corn leafhopper then you need to collect the insect and send it to a trained entomologist that can verify the identity of the insect under the microscope. Leafhoppers in general are fast moving insects but they can be collected in an insect net or using a handheld vacuum (see EPP-25-3). You can submit samples to the OSU Plant Disease and Insect Diagnostic Lab.
Please feel free to reach out to OSU Cropping Systems Extension Entomologist Dr. Ashleigh Faris with any questions or concerns. @ ashleigh.faris@okstate.edu
PRE-EMERGENT RESIDUAL HERBICIDE ACTIVITY ON SOYBEANS, 2025
Liberty Galvin, Weed Science Specialist
Karina Beneton, Weed Science Graduate Student.
Objective
Determine the duration of residual weed control in soybean systems following the application of Preemergent (PRE) herbicides when applied alone and in tank-mix combination.
Why we are doing the research
PRE herbicides offer an effective means of suppressing early-season weed emergence, thereby minimizing competition during the critical early growth stage. However, evolving herbicide resistance and the need for longer-lasting weed suppression underscore the importance of evaluating multiple modes of action and their residual properties alone and tank-mixed.
Field application experimental design and methods
Field experiments were conducted in 2022, 2023, and 2024 growing seasons in Bixby, Lane, and Ft. Cobb FRSU Research Stations across Oklahoma. Each herbicide (listed in Table 1) was tested individually, in 2-way combinations, 3-way mixtures, and finally as 4-way combinations that included all active ingredients listed at the label rate.
Soybeans were planted at rates between 116,000 and 139,000 seeds/acre from late May to early June, depending on the year and location. The variety used belongs to the indeterminate mid- maturity group IV, with traits conferring tolerance to glyphosate (group 9 mode of action), glufosinate (group 10), and dicamba (group 4). Not all soybean varieties have metribuzin tolerance. Please read the herbicide label and consult your seed dealer for acquiring tolerant varieties. Row spacing was 76 cm at Bixby and Lane, and 91 cm at Fort Cobb. PRE treatments were applied immediately after planting at each experimental location.
POST applications consisted of a tank-mix of dicamba (XtendiMax VG® – 22 floz/acre), glyphosate (Roundup PowerMax 3®- 30 floz/acre), S-metolachlor (Dual II Magnum® – 16 floz/acre), and potassium carbonate (Sentris® – 18 floz/acre). Applications were made on different dates, mostly after the first 3 weeks following PRE treatments. These timings were based on visual weed control ratings, particularly for herbicides applied alone or in 2-way combinations, which showed less than 80% control at those early evaluation dates. The need for POST applications also depended on the species present at each site, with most fields being dominated by pigweed, as illustrated in the figure below.
Results
Tank-mixed PRE herbicide combinations generally provided superior residual control compared to a single mode of action application (Shown in Figure 1). Timely post-emergent (POST) herbicide applications helped sustain high levels of weed suppression, particularly as the effectiveness of residual PRE declined.
Residual control of tank-mixed PRE
Some herbicides applied alone or in simple 2-way mixes, such as sulfentrazone + chloransulam- methyl and pyroxasulfone + chloransulam-methyl required POST applications within 20 to 29 days after PRE, indicating moderate residual control.
In contrast, 2-way combinations containing metribuzin, such as sulfentrazone + metribuzin and pyroxasulfone + metribuzin, extended control up to 50 days after PRE in some cases, highlighting metribuzin’s importance even in less complex formulations.
Furthermore, 3-way and 4-way combinations including metribuzin provided the longest-lasting control, delaying POST applications up to 51–55 days after PRE.
Injury of specific weeds
Palmer amaranth (Amaranthus palmeri) control in Bixby was consistently high (≥90%) at 2 weeks after PRE in 2022 and 2024 across all treatments. At 4 WAPRE, treatments containing metribuzin alone or in combination maintained strong control (90% or greater).
Texas millet (i.e., panicum; Urochloa texana) and large crabgrass (Digitaria sanguinalis) were effectively managed with most treatments delivering over 90% control early in the season and maintaining performance throughout. In 2024, control remained generally effective, though pyroxasulfone alone showed a temporary lack of control for Texas millet, and single applications declined in effectiveness against large crabgrass later in the season. These reductions were likely due to continuous emergence and the natural decline in residual herbicide activity due to weather. The most consistent late-season control for both species came from 3- and 4-way herbicide combinations.
Morningglory (Ipomoea purpurea) control reached full effectiveness (100%) only when POST herbicides were applied, across all years and locations. Their late emergence beyond the residual window of PRE herbicides reinforces the importance of sequential herbicide applications for season-long control.
Take home messages:
- Incorporating PRE and POST herbicides slows the rate of herbicide resistance
- Tank mixing with *different modes of action* ensures greater weed control by having activity on multiple metabolic pathways within the plant.
- Tank mixing with PRE herbicides could reduce the number of POST applications required, and
- Provides POST application flexibility due to residual of PRE application
For additional information, please contact Liberty Galvin at 405-334-7676 | LBGALVIN@OKSTATE.EDU or your Area Agronomist extension specialist.
Down and Dirty with NPK 