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Since 2008 I have served as the Precision Nutrient Management Extension Specialist for Oklahoma State University. I work in Wheat, Corn, Sorghum, Cotton, Soybean, Canola, Sweet Sorghum, Sesame, Pasture/Hay. My work focuses on providing information and tools to producers that will lead to improved nutrient management practices and increased profitability of Oklahoma production agriculture
Guest Author, Dr. Jake Vossenkemper; Agronomy Lead, Liquid Grow Fertilizer
New Research Comparing Ortho/Poly-Phosphate Ratios for In-Furrow Seed Safe Starter Fertilizers
- Ortho-phosphates are 100% plant available, but a high percentage of poly-phosphates in starter fertilizers convert to ortho-phosphate within just two days of application.
- This quick conversion from poly- to ortho-phosphate suggests expensive “high” ortho starter fertilizers are not likely to result in increased corn yields compared to seed-safe fluid starters containing a higher percentage of poly-phosphate.
- A field study conducted near Traer, IA in the 2016 growing season found less than 1 bu/ac yield difference between a 50/50 ortho:poly starter and high ortho-phosphate starter.
- High ortho starters cost more per acer than 50/50 ortho:poly starters, but do not increase corn grain yields.
Poly-phosphates Rapidly Convert to Plant available Ortho-Phosphates
Given poly-phosphates are not immediately plant available and ortho-phosphates are immediately plant available, this gives the promoters of “high” ortho-phosphate starters ample opportunity to muddy the waters. Nevertheless, the facts are that poly-phosphates are rather rapidly hydrolyzed (converted to) into ortho-phosphates once applied to soils, and this hydrolysis process generally takes just 48 hours or so to complete.
In Sept. of 2015, I posted a blog discussing some of the more technical reasons why the ratio of ortho- to poly-phosphates in starter fertilizers should have no impact on corn yields. For those that are interested in those more technical details, I encourage you to follow this link to the Sept. 2015 blog post: https://www.liqui-grow.com/farm-journal/.
While I was relatively certain that the ratio of ortho- to poly-phosphates in liquid starters should have no effect on corn yields, I decide to “test” this idea with a field trial in the 2016 growing season conducted near Traer, IA.
How the Field Trial Was Conducted
In this field trial, we used two starter products applied in-furrow at 6 gal/ac. Each starter had an NPK nutrient analysis of 6-24-6. The only difference between these two starters was the ratio of ortho- to poly-phosphate. One of these starters contained 80% ortho-phosphate and the other contained just 50% ortho-phosphate with the remainder of the phosphorous source in each of these two starters being poly-phosphate. Each plot was planted with a 24-row planter (Picture 1) and plot lengths were nearly 2400 ft. long. In total, there were 5 side-by-side comparisons of the two starter fertilizers that contained different ratios of ortho- to poly-phosphates.
Field Trial Results
In general, there were no large differences in yield between the two starters in any of the 5 side-by-side comparisons, except for comparison number 5 (Figure 1). In comparison number 5, the 50% ortho/50% poly-phosphate starter actually yielded 6 bu/ac more than the high ortho starter. But averaged over the 5 side-by-side comparisons, there was less than 1 bu/ac yield difference between the high and low ortho starters (P=0.6712).
In addition to finding no differences in grain yield between these two starters, the high ortho starters generally cost about $1 more per gallon (so $6/ac at a 6 gal/ac rate) than the low ortho starters. So the more expensive high ortho starter clearly did not “pay” its way in our 2016 field trial.
More Trials Planned for 2017
While our findings agree with other research-comparing ortho- and poly-phosphate starter fertilizers (Frazen and Gerwing. 1997), we want to be absolutely certain that our fertilizer offerings are the most economically viable products on the market. Therefore, I have decided to run this same field trial at one location in northern Illinois in 2017, and at one location in central Iowa in 2017. Stay tuned for those research results this fall.
Franzen D. and J. Gerwing. 2007. Effectiveness of using low rates of plant nutrients. North Central regional research publication No. 341. http://www.extension.umn.edu/agriculture/nutrient-management/fertilizer-management/docs/Feb-97-1.pdf (accessed 8 of Sept 2015).
Nutrient Management Specialist
Kansas State University
Is it important to have the proper ratio of calcium (Ca) and magnesium (Mg) in the soil? Producers may ask this question as they have their soil tested for nutrient levels in the summer before wheat planting begins. This question may also arise at the moment of lime purchase, which can be an important source of Ca and Mg.
Calcium and Mg are plant-essential nutrients. All soils contain Ca and Mg in the form of cations (positively charged ions, Ca++ and Mg++) that attach to the soil clay and organic matter; these are also the forms taken up by crops. The relative proportion of these elements, as well as the total amount in the soil, depends mainly on the soil parent material. In Kansas soils, the levels of Ca and Mg are typically high and crop deficiencies are rare.
Soils typically have higher Ca levels than Mg. Table 1 gives the amount and ratios of Ca and Mg for some soils in Kansas. Both nutrients are present in large quantities. Unusual cases of Ca or Mg deficiencies may be found in areas of very sandy soils.
|Table 1. Calcium, magnesium, and Ca:Mg ratio for several Kansas soils|
Why would the ratio of Ca to Mg be important? The concept of an optimum Ca:Mg ratio started in the 1940s under the “basic cation saturation ratio” theory. The theory is that an “ideal soil” will have a balanced ratio of Ca, Mg, and potassium (K). According to this theory, fertilization should be based on the soil’s needs rather than crop’s needs — focusing on the ratio of crop nutrients present in the soil. This concept of an ideal Ca:Mg ratio has been debated by agronomists over the years. The suggested ideal ratio according to the theory is between 3.5 and 6.0, but this has never proven to be of significance.
There is very little research evidence to support any effect, either positive or negative, of the soil Ca:Mg ratio on crop production and yield. What research studies have been conducted in the laboratory and in the field show no effect of Ca:Mg ratio on crop yield. Despite this, the promotion of the ratio concept persists today. Furthermore, the initial work that derived this concept did not differentiate between crop response (alfalfa) due to the change in Ca:Mg ratio and the improvement in soil pH from lime application. It is reasonable to conclude that crop response can be expected from changes in soil pH rather than any change in the ratio of Ca:Mg.
One example of research conducted on this topic over the years is shown in Table 2. In that experiment, McLean and coworkers demonstrated the lack of relationship between Ca:Mg ratio and crop yield for several crops. The range of Ca:Mg ratios observed for the highest yields were not different from those observed for the lowest yields. The conclusion from that study was that to achieve maximum crop yield, attention should center on providing sufficient levels of these nutrients rather than attempting to find an adequate ratio. Therefore when these nutrients are present in optimum levels for plant growth, the relative ratio in the soil seems irrelevant.
|Table 2. Ratio of Ca:Mg for five crop-years comparing the highest and lowest yields obtained|
|Yield level||Ca;Mg ratio|
|Highest five||5.7 – 26.8||5.7 – 14.2||5.7 – 24.9||5.7 – 14.0||5.7 – 26.8||6.8 – 26.8|
|Lowest five||5.8 – 21.5||5.0 – 16.1||2.3 – 16.1||6.8 – 21.5||8.2 – 21.5||5.7 – 21.5|
Adapted from: McLean, E.O., R.C. Hartwig, D.J. Eckert, and G.B. Triplett. 1983. Basic cation saturation ratios as a basis for fertilizing and liming agronomic crops. II. Field studies. Agronomy Journal 75: 635-639.Ada – 21.veeio of Ca:Mg for five crop-years comparing the highest and lowest yields obtainedto the diseaseeo produced by Dan Don
In conclusion, trying to manage the ratio of Ca:Mg should not be used for a nutrient application or liming program. The center of attention should be to ensure that levels of Ca and Mg in the soil will not limit optimum plant growth. The relative concentration of Ca and Mg in commercial ag lime can be highly variable, and application should be based on the effective calcium carbonate (ECC) to achieve a target soil pH.
Dorivar Ruiz-Diaz, Nutrient Management Specialist
Kansas State University
Jessica Pavlu, Graduate Research Assistant,
Tom A. Royer, Oklahoa State University Extension Entomologist
Co-Editors: Eric Rebek and Justin Talley; Oklahoma Cooperative Extension Service
On July 12, 2016, we found sugarcane aphids in a sorghum field in Caddo county that had exceeded treatment thresholds. Jerry Goodson, Extension Assistant in Altus, reported finding a sparse colony of sugarcane aphids in Tillman county last week. Most of the sugarcane aphid infestations that we have observed so far are located south of Interstate 40. We will continue to provide weekly reports of sugarcane activity throughout the rest of the summer growing season.
Oklahoma’s “Sugarcane Aphid Team” (which also includes Dr. Ali Zarrabi, Mr. Kelly Seuhs, Dr. Kristopher Giles from the Department of Entomology and Plant Pathology, USDA researchers Dr. Norm Elliott and Dr. Scott Armstrong, and Dr. Josh Loftin and Dr. Tracy Beedy from the Department of Plant and Soil Sciences), is conducting research to identify effective insecticides, resistant sorghum varieties, best cultural practices to avoid sugarcane aphid, and develop improved sampling and decision-making rules for treatment thresholds.
When scouting, make sure you are finding sugarcane aphid, as it can be confused with yellow sugarcane aphid. The sugarcane aphid (Fig.1) is light yellow, with dark, paired “tailpipes” called cornicles and dark “feet” called tarsi. The yellow sugarcane aphid (Fig. 2) is bright yellow with many hairs on its body and no extended cornicles.
Currently the suggested treatment threshold for sugarcane aphid is to treat when 20-30 percent of the plants are infested with one or more established colonies of sugarcane aphids. An established colony is an adult (winged or wingless) accompanied by one or more nymphs (Fig 3).
Two insecticides, Sivanto 200 SL, and Transform WD, provide superior control of sugarcane aphid. Sivanto can be applied at 4-7 fluid ounces per acre. Transform WG can be applied at 0.75-1.5 oz. per acre. It is important to achieve complete coverage of the crop in order to obtain the most effective control. Consult CR-7170, Management of Insect and Mite Pests in Sorghum http://pods.dasnr.okstate.edu/docushare/dsweb/HomePage for additional information on sorghum insect pest management.
Sorghum “Whorlworm” and “Headworm” Decisions
Tom A. Royer, Extension Entomologist
This week, I received several reports of “worms” feeding in the whorls of sorghum (Fig 4) which I identified as fall armyworms. I rarely recommend that a producer treat for fall armyworms infesting whorl stage sorghum. Why? because available research suggests that under rain-fed production, whorl feeding rarely caused enough yield loss to warrant treatment costs, AND more importantly, most insecticide applications provide poor control. The poor control is a result of difficult delivery of the insecticide into the whorl allowing the caterpillars to avoid contact. However, recent unpublished research shows that some new insecticides may provide effective control of fall armyworm in the whorl, so it is time to revisit my recommendations.
Recent unpublished research results conducted in irrigated sorghum out of Lubbock suggest that Prevathon®, Besiege®, and Belt® can provide acceptable control of the caterpillars in the whorl (even large caterpillars). Therefore, the second of the two reasons I listed above may no longer be true; they can be controlled. However, 1: these products were tested on irrigated sorghum 2: they are quite expensive 3: some products may flare sugarcane aphids and spidermites and 4: WE STILL DON’T KNOW HOW THEY IMPACT YIELD, thus, we are still “guessing” with regard to return on investment for control.
How has this information changed my recommendations? Keep in mind that the research in Texas was conducted in irrigated sorghum with a very high yield potential. Since Oklahoma growers typically grow rain-fed sorghum which has lower yield potential, my suggestion is to examine 30 plants (5 consecutive plants in 6 different locations) and split a few stalks to see where the panicle is located. If the panicles are close to emerging (boot stage), my “best guess” is to consider treating if 70% or more of the whorls are infested and there are an average of 1-2 live caterpillars present. Under this scenario, you would be protecting physical damage to the emerging head.
On choosing an insecticide I offer some things to consider. 1: the effective products may or may not be available. 2: some have the potential to flare sugarcane aphids and spidermites. 3: they are all expensive. Belt is still available for use, but EPA recently requested that Bayer voluntarily remove it from the market. Bayer refused, and asked for an administrative hearing. On June 1, an administrative law judge upheld EPA’s decision to cancel registration of Belt. Bayer is appealing and is scheduled to receive another review from the Environmental Appeals Board before July 6. If EPA prevails in the appeal process, Belt will no longer be available. However, Bayer says that Belt can still be sold, purchased and used during the appeals process.
I have little information on how Belt affects sugarcane aphids or spidermites. Besiege is a mixture of the active ingredient in Prevathon with an added pyrethroid. Research in Lubbock suggests that spidermites may flare with Besiege. We also know that any pyrethroid will flare sugarcane aphid. Prevathon has not shown the propensity to flare either spidermites or sugarcane aphids.
We are attempting to obtain data on the effectiveness of, and yield returns obtained from Prevathon to control fall armyworm in the whorl. Until I have more data, I can only say that a producer should carefully consider a decision to control “whorlworms”. The jury is still out as to whether controlling them is economically justified.
With regard to headworms, we have well-designed decision making capability coupled with solid treatment thresholds. USDA and University scientists developed a computer-based program that can calculate an economic threshold for headworms (Fig.5) and provide a simple sampling plan that tells the producer if threshold is reached (Fig.6).
Called the Headworm Sequential Sampling and Decision Support System (http://entoplp.okstate.edu/shwweb/index.htm), it uses input on the plant population, the crop’s worth and the control costs to calculate a treatment threshold.
Now, prepare for the tricky part! If we only had to consider one pest, I would advise selecting the insecticide that works best on that pest. However, we now have to consider sugarcane aphid in all of our sorghum pest management decisions. In my opinion, if sugarcane aphid is already starting, a producer must consider using either Transform or Sivanto. That narrows the choice options for combining another product to control headworms because pyrethroids could flare the aphids.
I have reviewed data from multiple years of insecticide trials throughout the SE US. The data suggests that products containing chlorpyrifos provide spotty control of headworms. Data that I have reviewed from other insecticide trials suggests that Prevathon and Blackhawk provide excellent control of headworms and Diamond® was also effective on headworms. For information on spray mix compatibility, talk to the local sales representatives for the products you have chosen.
Consult CR-7170, Management of Insect and Mite Pests in Sorghum http://pods.dasnr.okstate.edu/docushare/dsweb/HomePage for more information.
Wheat Disease Update – 14 May 2016
Bob Hunger, Extension Wheat Pathologist
Department of Entomology & Plant Pathology – 127 Noble Research Center – Oklahoma State University – Stillwater, OK
405-744-9958 (work) – email@example.com
This past week in addition to being around Stillwater, I attended field days in Canadian County (just west of Oklahoma City), Kay County (north of Ponca City), Kingfisher County (northwest of Oklahoma City) and Major County (west of Enid). Wheat I examined ranged from milk to medium dough. Some active stripe rust (producing spores) was still present in Major County, but only at low levels. Leaf rust is prevalent around Stillwater, with low levels of leaf rust found in Kay and Major Counties.
Symptoms of barley yellow dwarf (BYD) also were observed at all locations. As previously indicated, I observed only discolored (yellow to reddish-purple) flag leaves and no stunting indicating infection of BYDV by aphids occurred in the spring. One observation of note is that often with BYD the flag leaf will be discolored but leaves below the flag remain green as in the photo below. This is indeed BYD.
The Diagnostic lab also has continued to receive samples testing positive for Wheat streak mosaic virus and/or High plains virus. These samples have been from northern, northwestern and the panhandle regions of Oklahoma. For more information, see Fact Sheet EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-8987/EPP-7328.pdf
Finally, another disease that is making an appearance in Oklahoma this year is take-all. I have not observed take-all in Oklahoma now for many years; in fact, the last time we received a number of samples of take-all was back in the early 2000s. Take-all is favored by moist conditions and a neutral to alkaline soil pH. Abundant moisture starting a year ago and in areas of Oklahoma again this year have likely provided conditions favorable for this disease in a few areas. Take-all will first show as white plants in low-lying, wet areas after a period of hot days. I don’t think this will be a significant disease in Oklahoma this year, but wanted to bring it to your attention.
Reports/excerpts of reports from other states:
Colorado: Dr. Kirk Broders (Plant Pathologist); Colorado State University; Fort Collins, CO; May 11, 2016: “There has been good precipitation around the state this spring which has led to a good wheat crop, but also provides the potential for more foliar diseases than we usually see. Most of the wheat in the southeast has already headed out and there are low levels of stripe rust present, but likely will not impact yield especially where the wheat is further along. Wheat in the rest of the state ranges from booting to heading (Feekes 10 – 10.1). It is at this point that the flag leaf will also become fully emerged, and it will be important to ensure the flag leaf is protected in order to protect yield. I have received reports of stripe rust from multiple locations in eastern Colorado from Prowers County in the southeast and further north in Cheyenne, Kit Carson, Yuma, Washington and Arapahoe counties. Scott Haley mentioned he saw bacterial streak in the northeast part of Colorado and I have also received a couple reports and confirmed one report of Stagonosopora blotch on wheat in Washington County. Both reports were from wheat planted after a previous wheat crop. There were several reports of Stagonospora blotch in the state last year likely due to the significant amount of precipitation. This fungus is capable of surviving on wheat stubble and then infecting the successive crop given ample rainfall. Both Stagonospora blotch and stripe rust remain sporadically distributed and at low levels in most regions in the state, but with more predicted rain in the forecast growers may want to consider applying a fungicide once the flag leaf is fully emerged in order to ensure it is protected and the head is able to yield to potential. Certainly, they should take into consideration whether there is any foliar disease currently in the field or in their region, the potential yield of the crop and the cost of the fungicide to be applied, as well as the probability of cool, rainy weather in the forecast.”
Wisconsin: Dr. Damon Smith (Ast Prof – Field Crops Pathology); University of Wisconsin-Madison; May 11, 2016: “It was only a matter of time…. Today we confirmed the first observations of stripe rust in Wisconsin for 2016. Brian Mueller, Graduate Research Assistant in the Field Crops Pathology Lab at the University of Wisconsin-Madison found active stripe rust pustules in winter wheat in both southern and south central Wisconsin. In southern Wisconsin stripe rust was found in the Wisconsin Winter Wheat variety trial located in Sharon, Wisconsin. Stripe rust was at low incidence and severity on emerging flag leaves with some lesions manifesting as chlorotic flecks and not yet active. We speculate that the epidemic initiated recently. With the humid and rainy weather over the past several days, conditions have been ripe for symptom development. The second stripe rust confirmation was at the Arlington Agricultural Research Station in an integrated management trial for stripe rust. Again, incidence and severity were low on emerging leaves, therefore, we speculate that the epidemic has recently initiated. We have been actively looking for stripe rust as there have been numerous reports of epidemics in winter wheat in states to our south and west. Given the recent weather patterns we will likely see more stripe rust show up in the state. I suspect we will start to see fungicide sprayers active in wheat fields in the state given the fact that the epidemic onset is coinciding with the emergence of flag leaves. We will continue to monitor the situation carefully.”
This article is written by Dr. Josh Lofton
Oklahoma State University Cropping Systems Extension Specialist
Determining wheat yield loss:
The question on to how to manage wheat production that has suffered high potential yield loss can be quite challenging. High disease pressure and periods of dry conditions have been the main focus of this season’s wheat crop, but the recent storms have added to these issues with fields having >50% lodged wheat. While this may be a great concern when viewing this crop initially, a lodged or damaged wheat crop may still have decent yield potential. It is important to remember that, 50% lodging does not necessarily represent 50% yield loss. Many times the wheat crop will stand back up days or weeks after a lodging event. Overall, for a questionable stand of wheat, the best course of action might be to keep the stand and get the most yield possible from the crop. If you are considering planting a crop after failed or abandoned wheat, there are some important considerations before making the jump.
Insurance potential for a replacement crop
This will be the biggest catch for terminating a current wheat crop for a replacement summer crop. In many scenarios, once the wheat crop has begun to head this will be considered a double crop situation. In this instance many companies will not allow insurance to cover the following crop. Even if insurance is available for this double-crop scenario, at least three year yield potential numbers are frequently the minimum needed to receive this support. The best first steps for a grower to take when evaluating their fields planting of a replacement crop after a termination or hay is to check on their individual coverage and talk to their representatives before any action is taken.
Things to consider before moving into a summer crop:
One of the most important considerations for determining if and what potential crop could be planted following a non-harvested wheat crop is the chemistries used during the year. Table 1 gives rotational restrictions on some commonly used winter wheat herbicides. While this provides a summary or shortened list of herbicides and their rotational restrictions, producers should check individual labels if other herbicides were used. It should also be mentioned that minor plant injury could occur past the stated months following application given differences in soil conditions such as pH, soil moisture, and soil temperature.
Heavy wheat residue:
One thing that needs to be decided is how the grower will manage the heavy wheat residue associated with the failed crop. Certain situations exist that may result in limited to no residue (i.e. haying or heavy disease pressure); however, most producers will be faced with high residue load which may potentially be heavily matted and may pose challenges for producers to plant through. In these situations, producers may need to resort to tillage. The amount and intensity of tillage will greatly depend on the amount of residue left in field. In high residue situations, producers may need to run one or several primary tillage practices followed by a secondary or finishing tillage event. However, in lower residue conditions or if the producer has access to no-till equipment, no tillage may be needed to achieve a successful stand.
Overall cropping system:
When deciding to terminate an existing wheat crop and/or to plant a successive crop, decisions need to be evaluated at a systems level. Growers need to ask themselves whether this makes sense within their system and if it fits into their long-term system goals. If the original intent for the system was to double-crop following wheat harvest, it needs to be determined if the remaining economic benefit without the yield from the wheat crop. This may be at least partially alleviated if any profit can be made from the wheat crop (i.e. hayed) but needs to be evaluated on a specific field basis. The next question will be what the successive crop would have originally been? If a summer crop is planted, some systems will need a winter fallow as to not overstress the system, harvest the summer crop prematurely, or plant the successive winter crop past the appropriate timeframe. In this case it needs to be determined if that is suitable for the long-term system goals. Many of these scenarios exist and each could be beneficial or not within individual systems; however, growers need to evaluate these individually and determine what works best for their current situation and their long-term production goals.
Overall, the decision to move to a replacement crop can be very challenging. It cannot be stressed enough that in most situations maintaining the existing crop is likely the best option for most producers.
Cropping Systems Extension Specialist
376 Agricultural Hall
This article is written by Dr. George Rehm, University Minnesota, Soil Fertility Specialist (retired).
See more of Dr. Rehm’s blogs at agwaterexchange.com.
Use of strip trials as a learning as a way to learn is becoming more popular across the Corn Belt. This is to be expected. Crop producers have a thirst for information. With GPS technology and yield monitors, and the use of common sense, it’s not difficult to establish strip trials for the purpose of evaluating a concept or compare one or more products or rates of a product. There are, however, some important considerations for the conduct of a strip trial. These begin with planning before planting and continue with appropriate interpretation of the data following harvest. These considerations are summarized in the paragraphs that follow.
IN THE PLANNING PROCESS, SIMPLICITY RULES — Speaking from years of experience, when planning, it’s very easy to bite off more than you can chew. What looks easy or simple on paper can be a logistical problem when you go to the field. So, make comparisons simple. If comparing rates of nitrogen fertilizer for corn, for example use no more than three rates. It’s nice to have a control (the variable of interest is not used). The treatments to be compared must be repeated in the field at, least three times. If comparing rates of nitrogen fertilizer for corn, for example, use no more than three rates. It’s nice to have a control (the variable of interest is not used). The treatments to be compared must be repeated at least three times. The replication must be in the same field. It is almost a waste of time if fields are used as replications. If a control is used, it should also be replicated three times.
SITE UNIFORMITY — The day of selection of the site for a strip trial is probably the most day for the entire project. Soil uniformity is a must. There is no easy and simple procedure that can be used to correct for lack of soil uniformity at the site. There are several tools that can be used to select for soil uniformity. The Soil Survey should not be ignored. Soil test information based on either grid or zone sampling can also be very valuable. Time spent in selecting a uniform site is time well spent.
PRODUCTION PRACTICES — Once a specific comparison has been selected it’s very important to keep other production practices constant. For example, information from a strip trial designed to compare nitrogen rates has little value if varieties are changed in the trial area. Except for the factor of interest, keep all other production practices constant across the strip trial area. Two production practices that change across the strip trial cannot be changed at the same time. Careful planning for this type of project takes time and thought.
DATA COLLECTION — Unless there are special reasons to do otherwise, samples collected from treatments at any strip trial site should be collected at the same time. This practice reduces variability in the data. Considering yields, use of combine yield monitors or weigh wagons is certainly appropriate. Although this may be obvious to most, it is essential to record yields from each strip separately.
STATISTICAL ANALYSIS — There’s a reason for repeating (replicating) each treatment at least three times. The project is not complete until the data collected have been analyzed with a mathematical procedure called “statistical analysis”. I think that we all realize that there is variability across any field. With all factors being equal, we could combine four strips across any field and the yields would not be the same. So, when we see differences in yield, the obvious question is: “Is the difference in the yield the result of a real difference caused by the factor being considered or variability across the field?” Statistical analysis is the tool needed to answer this question. There is no other way to answer this question.
Let’s look at an example illustrating the importance of statistical analysis. Using strip trials in different counties, two rates of nitrogen were compared. There were three strips of each rate. For a field in Kandiyohi County with corn following a soybean crop, yields from the lower nitrogen rate (149 lb. soil + fertilizer N/acre) were 123, 157, and 170 bu./acre for the three strip receiving this rate. These three yields average to 150 bu./acre. For the higher nitrogen rate (199 lb. soil + fertilizer nitrogen), the three yields were 157, 176, and 166 bu./acre. This averages 171 bu./acre. Using these arithmetic averages, the initial conclusion is that the higher nitrogen rate was better than the lower nitrogen rate It would certainly appear that 171 bu./acre is better than 150 bu./acre. If statistical analysis is used, however, the difference in yield is not statistically significant. Why? This conclusion is the consequence of substantial variability among three replications. In other words, the arithmetic difference is due to variability in yield across the field rather than the factor being compared.
For the same project, a strip trial was used on a field in Carver County. The corn/soybean rotation was used. The low nitrogen rate was 102 lb./acre and the higher nitrogen rate was 151 lb./acre. Yields from the three strips with the low nitrogen were 181, 196, and 195 bu./acre with an average of 191 bu./acre. For the high nitrogen rate, yields from the three strips were 208, 210, and 207 bu./acre with an average of 208 bu./acre. Statistical analysis of this yield data showed that the difference between 191 bu./acre and 208 bu./acre was not due to variability in the field. It was, in fact, the result of the rate of nitrogen applied. Notice that variability among the three replications for each nitrogen rate was small. Thus, we can say with confidence that there was a REAL difference in yield caused by the rate of applied nitrogen.
Nearly everyone involved with strip trials wants to present an economic analysis of the yield data. This is logical. HOWEVWE, an economic interpretation is only valid if differences between or among treatments is STATISTICALLY SIGNIFICANT. Otherwise, we make a serious MISTAKE that could have serious economic consequences. For the Kandiyohi County field, the difference in yield could have been caused by treatment applied or natural variation in the field. We have no way of knowing the real cause. For the trial in Carver County, we are sure that the difference in yield was due to the rate of nitrogen applied. Use of statistical analysis allows us to reach this conclusion. Now economic interpretation can be applied to the results.
SUMMING UP — Use of strip trials is a good way to make comparisons between or among factors that affect crop production. In addition, these comparisons can be conducted in growers’ fields. However, it’s not an easy task to do an accurate job. Good planning is needed at the beginning and STATISTICAL ANALYSIS is essential at the end. There are too many comparisons where statistical analysis is ignored and only arithmetic averages are used. Without statistical analysis, there can be any number of interpretations of the data. Statistical analysis eliminates the potential for confusion.
Dr. George Rehm,
University of Minnesota
Nutrient Management Specialist (retired)
Tom A. Royer, Extension Entomologist
I have received scattered reports of cabbage aphids infesting canola racemes and low levels of green peach aphids feeding on canola leaves. Cabbage aphids are small, 2.0-2.5 mm (1/12 inches) blue-gray aphids with short cornicles. They are usually covered with a powdery wax coating. They are often found clustering on the developing panicle (Figure 1). They can cause plant stunting, distortion of growth, and flower abortion.
Green peach aphids are pale green to yellow (and sometimes pink) with long cornicles and antennae and measure 1/8 inch. They are found in winter and spring on leaves (Figure 2). Their feeding can cause stunting and defoliation. They can also transmit plant disease-causing viruses such as cauliflower mosaic and turnip mosaic viruses.
Scout for aphids by looking on the underside of the leaves, and racemes. For cabbage aphids, research conducted in Australia suggests that an insecticide application is justified if 20% of the racemes are infested with cabbage aphids.
For green peach aphids, research conducted by Dr. Kris Giles at OSU found that and average of one green peach aphid per plant can reduce seed yield by about 0.5 lb per acre. Thus, if the cost of an application is $10 per acre, and canola is bringing $0.2 per pound (quote from ADM Farmer Services 04/08/2016 www.adm.com), an infestation of 100 aphids per plant would cause yield loss of $10.00 (50 lb, x $0.2/pound) which is equal to the cost of the application. This is known as the ECONOMIC INJURY LEVEL (EIL). We typically set the ECONOMIC THRESHOLD (ET) below the EIL, in this case at 80% of the EIL (80 aphids per plant) to give time to schedule an application before the EIL is reached. Below is a set of suggested ECONOMIC THRESHOLDS, based on the cost of the application.
Application Cost Economic Injury Level Economic Threshold (Application cost/
0.5 lb/aphid x $0.2/lb (0.8 x EIL)
$8.00/acre 80 aphids/plant 64 aphids/plant\
$10.00/acre 100 aphids/plant 80 aphids/plant
$12.00/acre 120 aphids/plant 98 aphids/plant
$14.00/acre 140 aphids/plant 112 aphids/plant
Current recommendations for control of aphids in canola are listed in CR-7667, Management of Insect and Mite Pests in Canola which can be obtained online at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-3045/CR-7667web2009.pdf.
Transform® insecticide is no longer registered for use in canola as of November 11, 2015. Only existing stocks that have already been purchased and delivered to the grower before the cancellation can be applied according to the label.
Remember, green peach aphids have a history of developing resistance to pyrethroids, which are the primary registered insecticides for use in canola. Thorough coverage of an insecticide application is necessary to obtain optimal control.
If you notice natural enemy activity, especially lady beetles, and want to preserve their activity, keep several things in mind. Our research shows that Beleaf® insecticide is particularly benign to natural enemies because of its slow acting efficacy on aphids, which allows aphid-feeding beneficials to continue to eat them with little to no consequence on their biology. That being said, cabbage aphid may contain toxins that they acquire through their feeding which make them less palatable to some predators, and reduces their effectiveness as natural controls.
With all pesticides, review label restrictions for applications during bloom, as honeybees can be killed if exposed to several of the registered products. One registered product, Beleaf® (FMC Corporation) does not have any restrictions for application during bloom.