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I have been trying to write this blog addressing the yellow wheat for about two weeks now. But with finally finding a dry”ish” day or two and a lot of calls and emails about yellow wheat, I am just now getting to it.
So the short story is there is a lot of wheat out there in the state that is show signs of chlorosis, or yellowing. I wish I could say I have all the answers for you in this article, but I will have to lay heavily upon the agronomist best answer, “Well it Depends.”.
First we will start with the things I know least about and then move on to things that are more in my wheelhouse. In the last two weeks I have been on multiple email strings trying to chase down the cause of chlorosis in fields all over the state. One of these included Dr. Bob Hunger and the Plant Disease & Insect Diag Lab (PDIDL) and in one field his final thought was “So, my best guess is cold and wet soils along with fungi colonizing the older leaves that are starting to senesce.” At the same time I am finding regular occurrence of Tan Spot and Leaf Rust increase. All these pathogen cause some level of chlorosis and if you do not get down and pull some samples you will never know the cause.
A new for me this year is what I am calling the herbicide ding. I was able to get over a lot of my wheat that first week of March with a shot of herbicide, everything was almost to hollowstem. The wheat really got dinged. Very visual yellowing and stunting of the plants. Talking with Dr Manucheri, she had seen the same thing in her plots in Tipton. I have also visited several farmer fields with the same symptoms. Dr. Manucheri shared with me the Finesse label. Directly from the label “Temporary discolorations and/or crop injury may occur if herbicide is applied when the crop is stressed by severe weather conditions (such as heavy rainfall, prolonged cold weather, or wide fluctuations in day/night temps), disease or insect damage, low fertility, applications to course soils, or when applied in combination with surfactant and high rates of liquid fertilizer solutions.” This can be found on page 5, http://www.cdms.net/ldat/ldFSL002.pdf . You can just about mark off every weather and application condition mentions, on the same field.
Now to the yellow wheat I can comfortably talk about. There is nitrogen deficiencies out there. That should not come as a shock with the amount of rain we have received over the last couple months. I also believe that a fair amount of the wheat crop out there is a bit lacking on roots department.
The overarching wet cools soils that we have more than likely have led to reduced root exploration in some areas. And if you combine short roots with a nitrate leaching then the probability of N being out of the reach of the crop is high. Then the question is “Is there still time to do anything?”. The trip I look over the weekend (3/28, 3/29) that encompassed a great deal of the North Central Ok wheat belt showed me that the majority of the wheat had really progressed physiologically in the last two weeks. At this point, a positive return on N investment hinges on the stage the wheat is at.
Our delayed N work over the past several years show that we have maintained the yield on our trials even when fertilizer was delayed into the first week of April. https://osunpk.com/2019/08/14/how-long-can-wheat-wait-for-nitrogen-one-more-year-of-data/
This table shows the application dates of the 10 site years of the delayed nitrogen study. The first column is the location, to the right of the location is two rows the top is grain yield and the bottom is grain protein. Each of the following columns corresponds to an application date. Applications began at each study when the The colors are related to whether that application was statistically (Alpha=0.05) worse than, equal too, or better than applying nitrogen at the first sign of deficiency (0DAVD). For this comparison it is important to know that at no location did preplant have significantly greater yield than 0DAVD.In the majority of those years that first week of April corresponded with the growth stage Feekes 8, last leaf just visible. As the crop moves beyond that point, catching up did not happen. Currently there is wheat out there in the state that has not hit hollow stem (Feekes 6) and there is wheat at Flag leaf (Feekes 9).
The high rainfall totals we have could have also led to another deficiency sulfur. In the past S deficiency is fairly hard to find in Oklahoma. Our long history of low S using winter wheat and high sub-soil S levels have kept the response to Sulfur low, but not uncommon. Sulfur is a mobile nutrient and will also be lost via leaching especially in sandy soils in the northern part of the state. Sulfur deficient is different from N in that it shows in the newer growth as a general yellowing of crop. Kansas State has a lot of great resources on sulfur management in wheat. https://webapp.agron.ksu.edu/agr_social/m_eu_article.throck?article_id=2132
If your wheat is yellow and before you call the fertilizer applicator, first confirm it is nitrogen and or sulfur and not something else. A key point to nitrogen deficiency is that the cholorsis will be worst on the oldest leafs while new growth is green. If N deficiency is confirmed then figure out how far along your wheat is. If the crop is around hollow stem to Feekes 8, if you can get the N on soon there is a good chance to get your money back plus. Keep in mind with air temps above 60 degrees UAN will burn the tissue so it is best to use streamer nozzles, which will still burn but the tissue damage is lessened. If you do not have access to streamers you can dilute the UAN with water and use flat fan nozzles. Cutting the UAN with water reduce the impact of leaf burn, I typically recommend at least 2 part UAN to 1 part water, but a 1 to 1 is the safest.
If you have any questions or concerns please feel free to email any questions you may have.
When I started writing this blog (3.13.2105) Ok grain elevator cash bids for grain sorghum aka milo was 6.61-7.70 cwt (3.7-4.31 per bushel) and corn was at 3.64-4.06 per bushel. Meaning there is currently a premium on sorghum grain. This difference among other things has increased the interest in planting sorghum. Of late I have been quite successful, at least on a small-scale, at producing sorghum yield in the 120-150 bpa range, thanks to the advice of Rick Kochenower former OSU sorghum specialist. Both of us believe that every year many producers are leaving significant bushels on the table due to one or two miss steps. I wanted to take this opportunity to share what is in my opinion the keys in producing a bumper sorghum crop. I should note that the primary key is out of our control, rain.
Key 1. Planting date, the optimum planting date for grain sorghum is generally when soil temperatures reach 60° F and increase after planting. For much of the region that I believe is best suited for sorghum this falls between April 1 and April 15 for south of I40 and April 15 and May 1 north of I40. graph below shows the long-term average daily 4″ soil temp (bare soil) for Apache, Blackwell, Cherokee, and Vinita. It is easy to see how your location within the state can impact soil temps.
You should not forget however that tillage practices will also impact soil temps. The two graphs below show the long-term average daily 4″ soil temp for Cherokee and Blackwell for both bare soil and under sod. Note that when the soil is covered by residue it warms slower. The two figures also show that residue will have more impact in some areas more so than others.
My best word of advise is to keep a watchful eye on the Mesonet. While the long-term average is nice to know here in Oklahoma the difference in weather from one year to the next can be huge. The figure below shows the average daily 4″ soil temp (below sod) from Blackwell for the past five years. Link to Mesonet Soil Temp page Click here.
Another great resource is a report on planting date written by Rick Kochenower presented to RMA. Link to report.
Key 2. Hybrid selection, primarily maturity group selection. Rick has created a great graphic that helps put a planting date window with maturity group. It is always important to visit with your local seed dealer to find out what has been performing best in your region and consider the importance of stay-green, standablilty and disease packages. But for me the number one key is the selection of maturity group. This should be based upon planting date and harvest strategies. Below is a great graphic created by Rick, while this may not be scientific it is a great guide created via years of experience. I also recommend that if you are planting a significant amount of acres you should diversify your maturity groups. Not only does this spread out he harvest window but it also you to spread the risk of high temps coming early or late. An additional resource is the Sorghum Performance trial summary located on the Ok Panhandle Research and Extension Center website. Click here.
Key 3. Soil Fertility, while soil pH plays a big role on sorghum productivity but it is too late in the game to do much about it this year. So the most important things to keep in mind on fertilizing sorghum are your macro-nutrients nitrogen (N), phosphorous (P) and potassium (K). It is my opinion that historically producers have underestimated the yield potential of sorghum and therefore lost yield due to under application on N. You should expect more than 60 to 80 bushel out of your crop if you put the right seed in the ground, at the right time and in the right way.
Ask around look at Rick’s yield data, producers in N. Central Ok on a good soil should be going for 125+ bpa easy. Unfortunately you are unlikely to hit these yield levels if you fertilize for a 75 bpa crop. An easy rule of thumb on N fertilization is 1.2 lbs of N per bushel, for a more exact number take a look at the image below. This comes from the corn and sorghum PeteSheet and is the same table that comes from the Soil Fertility Handbook. (If you would like some Pete Sheets just send me an email requesting them at firstname.lastname@example.org, Link to PeteSheets page).
Key 4. Weed Control With sorghum utilizing a pre-plant herbicide with residual is extremely important due to the lack of over the top options. Most times proper weed control will be accomplished by utilizing concept treated seed and use of labeled rates of a pre-emergent grass control herbicide combined with atrazine.
While I primarily focus of the four keys above there are a few other important items to consider.
Population: Prefer to think in terms of seeds per acre instead of lbs per acre. This comes into to play with the use of a planter. Rick Kochenower says “for seeding rate(on 30 inch rows), it isn’t as critical as most people think it is. Because most guys in Oklahoma tend to under plant not over plant. I always suggested 45,000 but as you look at the last slide it really don’t matter much. The way I always liked putting it is to make you sure have enough out there to not have to replant, because being late hurts more than having to few too many or too few plants.”
Row spacing: I like 30, but many may not have a planter so I suggest at least plugging every other hole in the drill to be at a 12″-20″ spacing. Make sure your population is correct for your row spacing. For this consult with your local seed dealer to match cultivar with row spacing and proper population.
Insects: Scouting for aphids and head midge is very important, these little critters are yield robbers and can gum up the works at harvest.
Harvest prep: I almost put this as the fifth key. By chemically maturing/terminating your crop you are both able to increase harvest efficiency and preserve moisture for a following winter crop of wheat or canola.
While this is a good start I suggest a visit with your local OSU Extension educator, consultant or seed dealer for information about your specific situation. Just know the crop has great potential to yield big if treated right. I like to say don’t treat your sorghum crop like the stray you adopted, treat it like your hunting dog that you traveled halfway across the country to pick up. Good luck in 2015 and I hope the rains fall when and were needed.