About Me

Amanda De Oliveira Silva

Amanda De Oliveira Silva

I have served as an Assistant Professor and Small Grains Extension Specialist at Oklahoma State University since August 2019. I believe that close interaction with producers is vital to understand their production strategies and to establish realistic research goals. My program focuses on developing science-based information to improve the agronomic and economic viability of small grains production in Oklahoma and in the Southern Great Plains.

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First hollow stem update – 02/25/2021

Amanda de Oliveira Silva, Small Grains Extension Specialist

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8” or the diameter of dime) of stem below the developing grain head (full explanation). To give you a point of reference, the average FHS date over the past 20 years at Stillwater is March 6.

The photo shows the first hollow stem in wheat
Figure 1. First hollow stem occurs when hollow stem equivalent to the diameter of a dime (1.5 cm) is present below the developing grain head.

The latest FHS results from our forage trials in Chickasha (Table 1) and Stillwater (Table 2) are listed below. Few wheat varieties in Stillwater have reached or passed the 1.5 cm threshold.

The Mesonet First Hollow Stem Advisor and the updates we provide give an indication of the FHS stem conditions in a particular area. However, because of the number of factors that can influence when FHS occurs, it is extremely important to check for FHS on a field-by-field basis

Table 1. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/29/2020. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements from non-grazed plots. Varieties that have reached FHS are highlighted in red.

Table 2. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/21/2020. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements from non-grazed plots. Varieties that have reached FHS are highlighted in red.

Similar to previous years, we will monitor occurrence of FHS in our wheat plots at Stillwater and Chickasha and report the findings on this blog.

What will these cold temperatures do to the wheat crop?

Amanda de Oliveira Silva, Small Grains Extension Specialist

Weather forecasts indicate that temperatures will continue to drop in the next few days. The extent of possible damage from these below-normal temperatures on wheat will depend on several factors such as wheat developmental stage, soil moisture, snow cover, field conditions, and how cold and for how long these cold weather stays.

Most of the wheat in Oklahoma was dormant or just starting to come out of dormancy before this extreme cold front came in. The more advanced in growth the wheat is, the more exposed the growing point is and susceptible to injury. On the other hand, wheat fields planted late in December are also vulnerable as the wheat may not have had the time to develop its crown roots and tiller to sustain these cold temperatures. The most important part of the plant is the crown at this moment. We may see leaf damage, but if the crown remains alive, the plant can survive. Figure 1 provides a general guide to the minimum temperature threshold and its impact on yield. Keep in mind these temperature thresholds are not exact but provide a decent rule of thumb. Temperatures closer to the soil surface might be higher than those reported by weather stations one meter above the soil surface, especially if moisture is present. 

Figure 1. Temperatures that can cause injury to winter wheat at different growth stages. Source: Kansas State University publication C646: Spring Freeze Injury to Kansas Wheat.

Except for the western OK and Panhandle regions, most areas of the state were with adequate soil moisture, which helps to insulate the crop and improves survival chances. Also, if we receive the snow cover that is forecasted, the wheat will be more protected from the harsh conditions.

Regarding my last post that some varieties may have reached first hollow stem (FHS). Growers should keep in mind that FHS is based on the largest tiller on the plant. Even if we lose the largest tillers, we are fine as long as other tillers are viable and we have favorable growing conditions.

Figure 2. Leaf tips which have turned necrotic due to freezing temperatures. Photo taken in March 2017 courtesy of Josh Bushong, OSU Northwest area Extension agronomist.
Figure 3. More severe freeze damage causing the leaves to turn yellow-white with plants losing their overall turgidity. Source: Kansas State University publication C646: Spring Freeze Injury to Kansas Wheat.

Each freeze event is unique. It will take some time (1-2 weeks after the cold weather passes) to assess the actual impact of the below-normal temperatures on wheat. We will have to keep watching it as it will vary on a field-by-field basis.  


Contact your local county Extension office.

For additional read refer to:

Assessing Freeze Damage on Wheat

 C646 – Spring Freeze injury to Kansas Wheat

First hollow stem update

Amanda de Oliveira Silva, Small Grains Extension Specialist

First hollow stem (FHS) occurs just prior to jointing and is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8” or the diameter of dime) of hollow stem below the developing grain head (Fig.1). To give you a point of reference, the average FHS date over the past 20 years at Stillwater is March 6.

The photo shows the first hollow stem in wheat
Figure 1. First hollow stem occurs when hollow stem equivalent to the diameter of a dime (1.5 cm) is present below the developing grain head.

Several factors influence the onset of FHS. These include the wheat variety, location, temperature, available moisture, level of grazing, and planting date (later sown wheat will typically reach FHS later). Varieties can differ by as much as three weeks in onset of first hollow stem, and later maturity varieties generally reach first hollow stem later. Dual-purpose producers are encouraged to select varieties that are characterized as medium, late or very late in occurrence of FHS.

The latest FHS results for each variety planted in our forage trial at Stillwater are listed below (Table 1). A few varieties are at FHS (values at or above 1.5 cm), but values are likely to move slowly with current cold conditions in Oklahoma.

The First Hollow Stem Advisor and the updates we provide give an indication of the FHS stem conditions in a particular area. However, because of the number of factors that can influence when FHS occurs, it is extremely important to check for FHS on a field-by-field basis.

Methods for scouting for FHS:

  • Check for FHS in a non-grazed area of the same variety and planting date. Variety can affect FHS date by as much as three weeks and planting date can affect it even more.
  • Dig or pull up a few plants and split the largest tiller longitudinally (lengthways) and measure the amount of hollow stem present below the developing grain head. You must dig plants because the developing grain head may still be below the soil surface at this stage.
  • If there is 1.5 cm (~5/8″) of hollow stem present, it is time to remove cattle.

Table 1. First hollow stem results for each variety collected at Stillwater on 02/06/21. Plots were planted on 09/21/21. The threshold target for FHS is 1.5 cm. The value of hollow stem for each variety represents the average of ten measurements.

Similar to previous years, we will monitor occurrence of FHS in our wheat plots at Stillwater and Chickasha and report the findings on this blog.

Time to topdress wheat

Usually, the alarm for beginning wheat nitrogen (N) topdressing gets sounded right away in early January. A significant portion of the Oklahoma wheat belt has received a good amount of moisture in the past weeks, which was great to save the crop from the severe drought in the fall. However, some parts of the state would still benefit from additional moisture (Fig. 1).

In areas of the state where it is dry and dry deeper than the majority of the rooting zone (> 6”), you should not worry about filling up the nitrogen tank as long as the water tank is empty. In this case, the best option is to wait to apply N right in front of a real chance of rain. The good news is we still have time to get N applied and not limit yield potential if we do receive rain in those areas. For regions with good soil moisture, you could start making topdressing plans.

Fig 1. 30-day rainfall accumulation in Oklahoma. Figure courtesy from Mesonet.

Few crop inputs deliver as much return on investment as nitrogen fertilizer. It takes approximately two pounds of nitrogen, costing roughly $0.80-$1.00, to produce one bushel of grain worth about $5.60. Of course, nitrogen is not the only yield determining factor in a wheat crop. Also, the law of diminishing marginal returns eventually kicks in, but nitrogen fertilizer is still one of the safest bets in the house, especially when there is adequate soil moisture.

Topdress nitrogen fertilizer is especially important because it is applied and utilized when the plant is transitioning from vegetative to reproductive growth. Several things, including the number of potential grain sites, are determined just before jointing, and the plant must have the fuel it needs to complete these tasks. Jointing also marks the beginning of rapid nitrogen uptake by the plant which is used to build new leaves, stem, and the developing grain head. Our research has shown that approximately 20% of the aboveground nitrogen uptake at harvest is accumulated just prior to jointing, 50% at flag leaf emergence, and 70% at heading. The nitrogen stored in the plant vegetative parts is used to fill the grain later in the season, and the plant is dependent on this stored nitrogen to complete grain fill.

In the bullet points below, I will hit the major points regarding topdress nitrogen for wheat.

When to apply

  • To have full benefit, nitrogen must be in the rooting zone by the time wheat is jointing (which occurs around the end of February in southern OK and around mid-March in northern OK). Moisture is required to move nitrogen into the rooting zone. Since precipitation is usually very limited in January and February in Oklahoma, we need the nitrogen out on the field when the rain hopefully arrives back.
  • Suppose you decided to not apply any nitrogen prior to planting, due to residual soil nitrogen amounts or simply did not want to invest the money into the crop due to the dry weather. Did you happen to use an N-rich strip?
    • Yes, I did: If you currently see a difference between the N-rich strip and the rest of the field, then now would be time to begin making applications. For those producers who are using the Sensor Based Nitrogen Recommendation (SBNRC) system, your yield predictions and nitrogen recommendations generally become more accurate as the season progresses. However, growers wishing to hedge their nitrogen bet could apply a partial top dress now and supplement with a second top dress just before jointing, if SBNRC recommendations call for additional nitrogen. If you cannot see a difference, then wait until closer to jointing to make the call.  https://osunpk.com/2014/02/24/sensing-the-n-rich-strip-and-using-the-sbnrc/
    • No, I did not: Now would probably be ideal to start making those applications depending on fall growth and soil moisture levels. If soil moisture is present, considering apply enough N to reach the farm’s break-even yield goal. An N-rich strip helps take the guesswork out of adjusting your top dress N up or down based on your current crop conditions. Also, it is not late to apply an N-rich strip. Your county extension educator can provide more information on N-rich strips, and you can find more information on the web at npk.okstate.edu
  • Do not apply nitrogen to frozen ground. Nitrogen will move with water. If melting snow or frozen rain moves to the ditch, so will nitrogen applied to the soil surface.
  • Consider splitting or delaying top dress nitrogen applications to sandy soils until closer to jointing, as leaching can occur.

How much to apply

  • On average, it takes about 2 lbs/ac of N to produce a bushel of wheat. In addition, dual-purpose wheat requires 30 lbs/ac of N for every 100 lbs/ac of beef or 1,000 lbs/ac of forage removed. You can subtract your soil test NO3-N from these total requirements. Keep in mind that being short in N will limit yield and protein concentration in the grain.
  • Did you do a soil test? It is okay to adjust top dress N plans based on your current yield potential. When you submitted your soil test, you might have stated a 50 bu/ac yield goal requiring 100 lbs/ac of nitrogen; however, it is important to take a hard look and determine if this yield goal is still realistic for your current crop status. This does not suggest to adjust based on what you think the weather might do. Still, it is okay to take inventory and adjust your top dress N up or down based on current field conditions.
  • If you have good soil moisture, even if you want to limit your input, you need 40 to 60 pounds/ac of nitrogen at a minimum based upon your soil test and yield goal. If you already have N in the system, make sure to apply enough N for a 30-40 bushel wheat.

What source to use

  • The plant does not care about nitrogen source. A pound of nitrogen is a pound of nitrogen. Focus on getting the correct amount applied at the proper time, and choose your product based on price and application uniformity.
  • Use a source that can be applied uniformly. In my experience, spinner trucks or buggies are generally the least uniform. Air trucks or streamers are the most uniform.
  • Streamer nozzles almost eliminate leaf burn from UAN; however, leaf burn is generally not an issue until temperatures warm and/or you are applying fairly large amounts of UAN. Streamer nozzles are also not affected much by wind and deliver a uniform pattern in various conditions. Some studies indicate that banding of UAN through streamer nozzles will reduce nitrogen immobilization on crop residue. Keep in mind that you cannot tank mix herbicides when using streamer nozzles.
  • One pass herbicide/topdress applications are very efficient in terms of time and input costs, but in some scenarios, it can end up costing you more money. Consider two-pass applications when dealing with no-till fields, especially when canopy coverage is below 70%. This is due to the high probability that the nitrogen will be tied up when it hits the residue and will not be available for the current wheat crop. For a more in-depth discussion on tank mixing herbicides and UAN for top-dress see
Streamer nozzles provide uniform application of UAN in a wide variety of environmental conditions.
Poor nitrogen application can result in a streaked field. Some of the areas in this field were over fertilized while some where under fertilized, resulting in wasted nitrogen and less than optimal crop yield.

For more information, contact your local Extension office

Amanda Silva, Small Grains Extension Specialist at silvaa@okstate.edu

Brian Arnall, Precision Nutrient Management Specialist at b.arnall@okstate.edu.

Uneven wheat emergence and stand establishment – is my wheat going to make it?

Amanda de Oliveira Silva, Small Grains Extension Specialist

I have been watching some wheat fields consistently after that ice storm came in late October. I am currently seeing anything from good looking wheat fields to areas with incomplete, thin, and uneven stands. We might not see complete stands for a while as the wheat emergence seems to be very uneven, and the wheat is still slowly coming up (Figure 1).

Figure 1. Uneven wheat emergence in a field planted on October 16. Picture was taken on November 9, 2020.

The thin and uneven stand establishment of the current wheat crop is likely due to the severe drought from the end of September to most of October. Then, most of Oklahoma was hit by the ice storm during the last week of October, with some areas receiving up to 5 inches of rain. Although that rain came in a much-needed time, it could have created a crust in the soil preventing the coleoptile from breaking through the soil surface.

If the wheat fails to emerge as expected in your field, dig up the soil and look for an “accordion” like plant. If you see that wheat has emerged its first true leaf under the soil surface, and it has been sitting there for a week or more, it will probably not going make it (Figure 2).

Figure 2. Wheat that has emerged its first true leaf under the soil surface will lose viability after one week or so. Field planted on October 21. Picture taken on November 9, 2020.

However, I am seeing crinkled coleoptiles in fields around Stillwater that are coming up slowly and will be fine. The crinkles probably occurred when the heavy rain occurred during the ice storm, but it was not enough to prevent the coleoptile from continuing to grow and pushing through the soil surface for the most part (Figure 3).

Figure 3. Part of the coleoptile got crinkled due to heavy rain and light soil crusting during the emergence period. Still, most of the plants seem to continue growing and breaking through the soil surface. Field planted on October 21. Picture was taken on November 9, 2020.

Overall, our variety trials that were planted sometime in October are coming up nicely, but we might not have a complete stand for a little while in some locations. Robert Calhoun, the Senior Agriculturalist of OSU Small Grains Program.

Some fields that were planted in early-mid October is also just now starting to emerge near Kay County. Shannon Mallory, Kay County Extension Educator.

About 95% of the wheat in our variety trial at Altus has emerged and shows adequate stands (planted on September 29). Gary Strickland, the Jackson County Extension Agriculture Educator and Southwest Research and Extension Center Regional Agronomist.

Josh Bushong, the OSU Area Extension Agronomy Specialist, reported in his Ag Insights November report that most of the fields in the North Central region are showing thin and uneven stands. He also mentioned this would likely have a small effect for grain only-producers.

As a summary, most of the fields that I am seeing or hearing about that were planted in October are still coming up. Wheat growth is a function of temperature. The cooler temperatures and lower cumulative growing degree days in the coming months will slow down growth until March or so. Plants may compensate to a certain extent for that reduced stand, and wheat producers aiming for grain-only production should not be concerned yet.

The plant on the right is likely not going to make it as the first leaf seemed to be stuck in the leaf sheath and would not to be able to emerge properly.
Incomplete wheat stand for a field near Stillwater planted on October 21. This field had enough moisture for wheat to begin germination as soon as it was planted, but emergence was hindered by the excessive rain from the ice storm that took place during the week of October 26, 2020.
Wheat is looking good at the forage trial in Stillwater. Although, it would benefit for an additional drop of water. Planted on September 21, 2020. Picture taken on November 16, 2020.
Wheat demonstration plots planted on September 21 (on the back) and on October 16 (in the front). Picture taken on November 16, 2020.

Wheat producers – What should we do with dry conditions in the forecast?

Amanda de Oliveira Silva, Small Grains Extension Specialist

I feel like this year’s planting season started like “Hurry up and wait! ” as my colleague Gary Strickland would say.

We had a great start with dual purpose wheat planting. There were lots of drills rolling around the state, and we were able to plant our dual-purpose trials in good soil moisture at 1 to 1.5 inches deep. However, with the wind blowing hard, temperature in the 80-90’s in some days, and lack of rain in the past few weeks, the soil has been drying up quickly in many areas of the state. There is a small or no chance of rain in the forecast for the next two-three weeks, and I am hearing producers discuss whether to park their drill for now or dust in wheat.

According to Wes Lee, the Oklahoma Mesonet Ag coordinator, rainfall is going to be very limited unless one of the tropical storms moves further west than expected. Dewpoints are very low, so if a rain occurs it will be light. He also mentioned that our current situation is a result of the moderate La Nina ENSO pattern, which tends to bring the driest falls and winters to Oklahoma. Gary McManaus, the Oklahoma Mesonet State Climatologist, says that predictions are not favorable at this moment, and we will likely see drought development and intensification by the end of the month and year in Oklahoma. 

As of October 4th, 45% of Oklahoma wheat was already planted and 20% emerged, which is about the same as the 5-year average (USDA-NASS, 2020). They also reported that we are 54% short and 34% adequate in topsoil moisture, and 33% short and 56% adequate in subsoil moisture. Figure 1 shows the 4” plant available water in the soil at this time of the year for 2019 and this year.

Figure 1. The 4” plant available water in the soil at this time of the year for 2019 (top) and this year (bottom). Figures courtesy Oklahoma Mesonet.

With a likely drought scenario for fall and dry conditions advancing quickly in our state, it is good to have in mind the possible effects of drought on the wheat germination and early growth.

Wheat germination and emergence in dry soils

The most important physiological requirement for wheat to germinate and sustain the developing seedling is soil water. Therefore, planting decisions needs to be based on a combination of available soil moisture and expected rainfall. In addition, other factors such as adequate seeding depth, sowing date, soil fertility, seed treatment, seed quality, etc. should be considered to guarantee a good crop establishment. For more information, check our previous blog post (planting-date-and-seeding-rate-considerations-for-winter-wheat) and the materials on our website.

Wheat seeds need a minimum water content of 35 to 45 % of its dry weight to initiate germination, and germination will increase as moisture levels increase. Dry soils can still have a relative humidity of 99%, and that can be enough moisture for seeds to germinate, it might just take longer than if it were in moist conditions. My concern with the current situation in Oklahoma, is the lack of rain in the forecast. This could result in enough moisture to start the germination process in certain areas of the state, but the seedling emergence and growth could be compromised if we don’t see any rain soon.

Wheat sown at about 1″ deep at Afton, OK on October 1, 2020. Photo: Amanda Silva.

What happens if the soil completely dries out before wheat emergence?

There are three phases during the germination process; water absorption, activation for when the seed coat is ruptured, and visible germination for when the radicle emerges, followed by the seminal roots and coleoptile. These processes will start and stop depending on the soil moisture. Thus, if the soil dries out before the roots and shoots are visible, the seed remain viable and the germination will be paused and continue once water is available. However, if the soil dries out after those structures are emerged (approximately 4-5 days after germination has begun), the seedling may not tolerate the lack of water resulting in loss or incomplete stand.

What should I do then? Choose your battle!

The optimal time for planting wheat in a grain-only system in Oklahoma is around Mid-October. So, I would say we still have a week of wiggle room to decide what do. There are different ways we can go about it, but we must keep in mind that there is always risk involved when planting wheat in dry conditions.

If you decide to dust in your wheat and wait for rain for wheat to germinate, watch your seeding depth. The optimum seeding depth to plant wheat is about 1-1.5” deep. We typically don’t have as many issues with winterkill in Oklahoma as they do in more northern states, so I am comfortable with dusting in at about 0.75 – 1” deep. Planting at 0.5” or less is too shallow in most circumstances. Also, there is always a chance for pounding rain occurring and forming soil crusts which makes it difficult for the coleoptile to push through the soil surface and may result in poor emergence. Fields with stubble cover may be less affected by pounding rain and reduce the risks of soil crusts forming. If the forecast follows through, and we receive rain in the next weeks, it would be light, and that could cause wheat to emerge but may be not enough for wheat to continue growing. Most of the field I visited in the past days had good subsoil moisture, so that could help!

If you decide to plant deeper to reach moisture, be careful with the coleoptile length of the variety you have, and make sure it has a long-enough coleoptile that will allow emergence if conditions are favorable. Consider increasing seeding rate to compensate for the low emergence which is prone to occur in this situation.

Should we wait for rain to plant then? This is a farm by farm call and it depends on which source of risk you find most comfortable. Personally, I would rather plant my wheat in the optimal planting window and adequate seeding depth than waiting for a rain that may take too long to happen or missing my optimal planting window. If the latter is the case, make sure to bump your seeding rate to try to compensate for the reduced time for tillering. Planting wheat at optimal time allows for more time for root growth in seedlings, helping the crop to have a quicker establishment under dry conditions and possibly help the plant to scavenge for water that is available deeper in the soil profile.

Our cooperator Keneth Failes preparing the field for planting wheat in Cherokee, OK. October 5, 2020. In this location, we were able to plant wheat at about 1” deep into moisture. We also found great subsoil moisture in this field. Photo: Amanda Silva.

Are there any specific agronomic traits that could help wheat seedling growth under water stress?

Traits that could help with seedling growth in dry conditions are the coleoptile length, which allows to plant a little deeper in moisture and good emergence (if deep planting is the practice of your choice). There are indications that sowing wheat varieties with larger seed may help to reduce the negative effects of drought during early growth (Mian and Nafziger, 1994). In general, the greater reserve of larger seeds results in a faster germination and crop establishment by increasing root growth and tiller production. Although, there are varieties with small seed size that germinate better than larger seeded varieties, demonstrating that genetics can also play an important role on the ability of variety to germinate in dry soils.

Wheat is known to be a resilient crop and to adapt to the low soil water availability, wheat that has already emerged will try to reduce transpiration (i.e. water losses from leaves) by reducing tillering and forage production.

Summary for managing wheat in dry conditions

Planting options: Dust in wheat at 0.75 – 1” deep, plant deeper to reach moisture, or just wait for a possible rain

Optimal timing for planting grain-only systems is Mid-October

Increase seeding rate if planting later than the optimal time

Plant varieties with long coleoptile length if planting deeper to reach moisture

There is no need for additional N in the fall as crops will not be using N in dry conditions

Wheat stand at Keyes, OK on October 7, 2020. Planted on September 22, 2020. Photo: Robert Calhoun, the Senior Agriculturalist of OSU Small Grains Program.
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Good stand for wheat that was planted on September 21 at Stillwater, OK. Photo: Amanda Silva.

Don’t hesitate to contact your County Extension office.

For references cited in this post and additional information, see below:

GRDC. Grain Research and Development Corporation, Australia. 2016. Wheat – Plant growth and physiology. https://grdc.com.au/__data/assets/pdf_file/0026/370673/GrowNote-Wheat-North-04-Physiology.pdf

Lollato R. and Holman J. 2020. Considerations when planting wheat into dry soil. K-State Agronomy eUpdate – Issue 821. https://eupdate.agronomy.ksu.edu/article_new/considerations-when-planting-wheat-into-dry-soil-409

Mesonet Oklahoma http://www.mesonet.org/index.php/forecast/local_and_regional

Mian and Nafziger, 1994. Seed Size and Water Potential Effects on Germination and Seedling Growth of Winter Wheat. Crop Science. 34(1), 169-171. https://doi.org/10.2135/cropsci1994.0011183X003400010030x

Shroyer J.P., Kok H., and Thompson C.R. Planting Practices in Wheat Production Handbook. K-State C529. https://bookstore.ksre.ksu.edu/pubs/c529.pdf.

USDA-NASS, 2020. Oklahoma Crop Progress and Condition. October 5, 2020. https://www.nass.usda.gov/Statistics_by_State/Oklahoma/Publications/Crop_Progress_&_Condition/2020/ok-cw-10-04-2020.

Considerations to Make before Planting Wheat this Fall – Wheat Disease Update – 27-Aug-2020

This article was written by Dr. Bob Hunger, Extension Wheat Pathologist and Dr. Tom Royer, Extension Entomologist

Planting date:  Much of the winter wheat sown in Oklahoma is used as a dual-purpose crop. In such a system, wheat is grazed by cattle from late fall through late winter/early spring and then harvested for grain in early summer.  In a grain-only system, wheat is generally planted in October, but in a dual-purpose system wheat is planted in early to mid-September to maximize forage production.  Planting wheat early significantly increases the likelihood that diseases and insect pests such as mite-transmitted viruses, the aphid/barley yellow dwarf complex, root and foot rots, and Hessian fly will be more prevalent and severe.  For more detailed information on planting date and seed treatment considerations on wheat, see CR-7088 (Effect of Planting Date and Seed Treatment on Diseases and Insect Pests of Wheat) at: http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-7836/CR-7088web2012.pdf

Mite-transmitted virus diseases.  These virus diseases are transmitted by wheat curl mites (WCMs) (Figure 1), and include wheat streak mosaic (WSM), high plains disease (HPD), and Triticum mosaic (TrM).  Of these, WSM is the most common. WCMs and these viruses survive in crops such as wheat, corn, and sorghum as well as many grassy weeds and volunteer wheat. In the fall and spring, WCMs spread to emerging seedling wheat, feed on that seedling wheat, and transmit virus to the young wheat plants.

      Given this disease cycle, it is easy to see several factors that determine the incidence and severity of these diseases.  First, controlling volunteer wheat and other grassy weeds that serve as alternative hosts for the mite and the viruses is imperative to help limit these diseases. Often an infected field of commercial wheat is growing immediately adjacent to a field left fallow during the fall and winter (Figure 2).  The fallow field contained abundant volunteer wheat and grassy weeds from which WCMs carrying Wheat streak mosaic virus (WSMV) spread into the commercial field.  Wheat infected in the fall will be severely damaged the next spring.  Wheat infected in the spring also is damaged, but not as severely as wheat infected in the fall.  Hence, it is imperative to do yourself and your neighbors a favor by controlling volunteer wheat and grassy weeds in fields left fallow – especially, if they are adjacent to commercial wheat fields.

        A second factor linked to the severity of these mite-transmitted virus diseases is planting date.  Early planting dates associated with grazing provides for a much longer time period in the fall for mites to spread to and infect seedling wheat.  Planting later in the fall (after October 1 in northern OK and after October 15 in southern OK) and controlling volunteer wheat are the two practices that can be employed to help manage these diseases.  It is extremely critical that volunteer wheat is completely dead for at least two weeks prior to emergence of seedling wheat because WCMs have a life span of 7-10 days.  Thus, completely killing or destroying volunteer wheat for a period of at least two weeks prior to emergence of seedling wheat will greatly reduce mite numbers in the fall.

        The incidence and severity of these mite-transmitted virus diseases as affected by planting date can be illustrated by the number of samples that tested positive for WSMV and HPV during each of the last three years.  In 2017, which was the last year mite-transmitted virus diseases were prevalent in Oklahoma, 103 wheat samples were tested by the Plant Disease and Insect Diagnostic Lab at OSU for presence of mite-transmitted viruses.  Of these 103 samples, 69 (67%) tested positive for WSMV and 22 (21%) tested positive for HPV.  In 2018, only 12 of 126 (10%) samples tested positive for one or both of these viruses.  In 2019, only 21 samples were submitted for testing with 7 samples (33%) testing positive for WSMV (no positives for HPV).  In 2020, few samples (less than 5) tested positive for any of these viruses.  This lower number of positive samples in 2019 and 2020 likely was the result of an overall later planting date of wheat in the fall of 2018 due to wet conditions and in fall 2020 due to extremely dry conditions.  I believe this later planting date in conjunction with more awareness and action in limiting the green bridge helped to lower the incidence and severity of the mite-transmitted viruses in Oklahoma in both 2019 and 2020. 

        Finally, seed treatments and insecticides are not effective in controlling the mites or these mite-transmitted virus diseases.  Regarding resistant varieties, there are several winter wheat varieties that have resistance to either WSM or the curl mites, but the adaptation of these varieties to Oklahoma is limited, and the resistance is not typically an absolute resistance to the disease.  Hence, severe and continuous disease pressure especially at higher temperature (greater than about 75 F) can overcome the resistance.  For more information on mite-transmitted virus diseases, see OSU Fact Sheet 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

Figure 1. Wheat curl mites and symptoms of wheat streak mosaic.

Figure 2. A commercial wheat field (right) growing adjacent to a field (left) in which volunteer wheat and grassy weeds were not controlled until the spring. The commercial field begin to show WSM symptoms in late March and the disease became severe as the spring progressed.

Aphid/barley yellow dwarf (BYD) complex:  Viruses that cause BYD are transmitted by many cereal-feeding aphids (Figure 3).  BYD infections that occur in the fall are the most severe because virus has a longer time to damage plants as compared to infections that occur in the spring.  Several steps can be taken to help manage BYD.  First, a later planting date (after October 1 in northern Oklahoma and after October 15 in southern Oklahoma) helps reduce the opportunity for fall infection. Second, some wheat varieties tolerate BYD better than other varieties; however, be aware that no wheat variety has a high level of resistance to the aphid/BYD complex.  For a listing of reaction of wheat varieties to BYD, other diseases and insect pests, and agronomic traits there are several sources available including variety comparison charts from Oklahoma State University (http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-6107/PSS-2142web2018.pdf) and Kansas State University (https://bookstore.ksre.ksu.edu/pubs/MF991.pdf), and the annual wheat variety publication titled, “Wheat Varieties for Kansas and the Great Plains by Layton Ehmke (34 Star Publishing Inc.; layton@34starpublising.comhttps://thewheatfarmer.com; 1-844-643-0170).  Third, control aphids that transmit the viruses that cause BYD.  This can be done by applying contact insecticides to kill aphids, or by treating seed before planting with a systemic insecticide.  Unfortunately, by the time contact insecticides are applied, aphids frequently have already transmitted the viruses that cause BYD.  Systemic seed-treatment insecticides containing imidacloprid or thiamethoxam can control aphids during the fall after planting.  This may be particularly beneficial if wheat is planted early to obtain forage.  Be sure to thoroughly read the label before applying any chemical.

Figure 3. Spot in field (left) of barley yellow dwarf (BYD) as would be seen in March or April. Many types of aphids (for example, greenbug; right) transmit the viruses that cause BYD.

Hessian fly:  Hessian fly (Figure 4.) infestations can occur in the fall and spring.  Fall infestations arise from over-summering pupae that emerge when climate conditions become favorable.  In states north of Oklahoma, a “Hessian fly free” planting date often is used to help limit fall infestations by Hessian fly.  However, such a planting date does not apply in Oklahoma because Hessian fly can emerge in Oklahoma as late as December (Figure 5.).

        Delayed planting (after October 1 in northern Oklahoma, and after October 15 in southern Oklahoma) can help reduce the threat of Hessian fly, but a specific “fly free date” does not exist for most of Oklahoma as it does in Kansas and more northern wheat-growing states.  This is because smaller, supplementary broods of adult flies emerge throughout the fall and winter.  A number of varieties are resistant to Hessian fly; for a listing of reaction of wheat varieties to Hessian fly, other diseases and insect pests, and agronomic traits there are several sources available including variety comparison charts from Oklahoma State University (http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-6107/PSS-2142web2018.pdf) and Kansas State University (https://bookstore.ksre.ksu.edu/pubs/MF991.pdf), and the annual wheat variety publication titled, “Wheat Varieties for Kansas and the Great Plains by Layton Ehmke (34 Star Publishing Inc.; layton@34starpublising.comhttps://thewheatfarmer.com; 1-844-643-0170).  Hessian fly infestations can be reduced somewhat by destroying volunteer wheat in and around the field at least two weeks prior to emergence of seedling wheat.  Seed treatments that contain imidacloprid or thiamethoxam will also help reduce fall infestations of seedling wheat, especially if combined with delayed planting and volunteer destruction.  For more information on Hessian fly, see OSU Fact Sheet: EPP-7086 (Hessian fly Management in Oklahoma Winter Wheat) at:http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-6189/EPP-7086web2015.pdf

Figure 4. Adult Hessian fly (left) and larvae and pupae of the Hessian fly (right)

Figure 5. Emergence of Hessian fly in Oklahoma by month from 2011-2013.

Root and foot rots:  These are caused by fungi and include several diseases such as dryland (Fusarium) root rot, Rhizoctonia root rot (sharp eyespot), common root rot, take-all, and eyespot (strawbreaker).  Every year samples are received in the lab that are diagnosed with root rot.  Typically wheat affected by seedling/root rots are either submitted in the fall when wheat is in the seedling stage or in later May and early June as plants are maturing.  Germinating seeds and seedlings have small root systems that if infected impacts seed germination and seedling emergence (Figure 6).  Later in the season (late May/early June), root rots again become apparent as maturing plants are unable to obtain sufficient moisture to finish grain development especially if drought conditions are present.  In mature plants, white heads often indicates the presence of root rot (Figure 7).

        In 2017-2018, the incidence and severity of root rots across Oklahoma dramatically increased compared to the 2016-2017 season.  This increase likely resulted from weather conditions that favored the root rots along with heat and drought in May/June of 2018 that promoted white heads to develop.  Dryland (Fusarium) root rot was the most common root rot observed in 2018, and caused significant damage to wheat in southwestern, western, northwestern OK as well as the panhandle.  In 2018-2019, dryland (Fusarium) root rot again became prevalent across much of Oklahoma, but was not as damaging as the previous year likely because ample moisture and cool temperatures meant that water stress on plants was much less than in 2017-2018.  Root rots were only sparsely observed in 2019-2020 and only at low severity. Controlling root and foot rots is difficult.  There are no resistant varieties, and fungicide seed treatments with activity toward the root and foot rots are effective in protecting germinating seed and emerging seedlings, their activity usually involves early-season control or suppression rather than control at a consistently high level throughout the season.  Often, there also are different “levels” of activity related to different treatment rates, so again, CAREFULLY read the label of any seed treatment to be sure activity against the diseases and/or insects of concern are indicated, and be certain that the seed treatment(s) is being used at the rate indicated on the label for activity against those diseases and/or insects.  Later planting (after October 1 in northern Oklahoma and after October 15 in southern Oklahoma) also can help reduce the incidence and severity of root rots, but planting later will not entirely eliminate the presence or effects of root rots.  If you have a field with a history of severe root rot, consider planting that field as late as possible or plan to use it in a “graze-out” fashion if that is consistent with your overall plan.  For some root rots, there are specific factors that contribute to disease incidence and severity.  For example, a high soil pH (>6.5) greatly favors disease development of the root rot called take-all.  OSU soil test recommendations factor in this phenomenon by reducing lime recommendations when continuous wheat is the intended crop. Another practice that can help limit take-all and some of the other root rots is the elimination of residue.  However, elimination of residue by tillage or burning does not seem to affect the incidence or severity of eyespot (strawbreaker).

Figure 6. A healthy plot of wheat in the fall as a result of using a seed treatment (left); a poor stand of wheat in the fall in a non-treated plot; a healthy seedling (left) compared to two seedlings (center and right) showing symptoms of common root rot. Notice the darkened sub-crown internode on the seedlings in the center and on the right as well as the reduced top growth compared to the healthy seedling on the left.
Figure 7. White heads indicative of root rot (left); darkened roots indicative of take all root rot (center); wheat killed by dryland root rot split open to show the pinkish growth of the causal fungus, Fusarium (right).

Seed treatments:  There are several excellent reasons to plant seed wheat treated with an insecticide/fungicide seed treatment.  These include:

1.      Control of bunts and smuts, including common bunt (also called stinking smut) and loose smut.  The similarity of these names can be confusing.  All affect the grain of wheat, but whereas common bunt spores carryover on seed or in the soil, loose smut carries over in the seed.  Seed treatments labeled to control bunts and smuts are highly effective.  If common bunt (stinking smut) was observed in a field and that field is to be planted again with wheat, then planting certified wheat seed treated with a fungicide effective against common bunt (stinking smut) is strongly recommended.  If either common bunt (stinking smut) or loose smut was observed in a field, grain harvested from that field should not be used as seed the next year.  However, if grain harvested from such a field must be used as seed wheat, treatment of that seed at a high rate of a systemic or a systemic + contact seed treatment effective against common bunt (stinking smut) and loose smut is strongly recommended.  In 2020, loose smut in fields and common bunt in harvested grain was observed at higher incidence and severity than for several years, so I strongly recommend planting certified wheat seed that was been treated with a fungicide labeled for control of bunt and smut.  For more information on common bunt (stinking smut) & loose smut, see: http://www.entoplp.okstate.edu/ddd/hosts/wheat.htm and consult the “2020 OSU Extension Agents’ Handbook of Insect, Plant Disease, and Weed Control (OCES publication E-832),” and/or contact your County Extension Educator.

2.      Enhance seedling emergence, stand establishment and forage production by suppressing root, crown and foot rots.  This was discussed above under “Root and Foot Rots.”

3.      Early season control of the aphid/BYDV complex.  This can be achieved by using a seed treatment containing an insecticide.  Be sure that the treatment includes an insecticide labeled for control of aphids.

4.      Control fall foliar diseases including leaf rust and powdery mildew.  Seed treatments are effective in controlling foliar diseases (especially leaf rust and powdery mildew) in the fall, which may reduce the inoculum level of these diseases in the spring.  However, this control should be viewed as an added benefit and not necessarily as a sole reason to use a seed treatment.

5.      Suppression of early emerged Hessian fly.  Research suggests that some suppression can be achieved, but an insecticide seed treatment has little residual activity past the seedling stage and Hessian fly often infests wheat after the seedling stage.

Oklahoma Wheat Harvest Completed for the Most Part with the State 99% Finished – Harvest Report June 29, 2020

Courtesy Oklahoma Wheat Commission

Wheat harvest is now complete in most regions of the state, with a few combines finishing up in parts of the Panhandle as well as Northern Oklahoma. This has been one of the fastest wheat harvest that we have seen in some time. The weather in all regions was favorable once machines started rolling in Southwest Oklahoma and allowed progress to move extremely fast from border to border. The Oklahoma Wheat Commission is calling wheat harvest 99% finished and this will be the final harvest report for the 2020 season. Test weight averages across the state have been extremely favorable in all regions, with most of the crop coming in at 61 lbs. to 64 lbs. per bushel.

Yields in Southwest and South Central Oklahoma varied with much of the wheat having low yields (ranging from the mid teens to high 20’s) due to excessive freeze damage that took place on April 15th. Yields were much better in central Oklahoma, with several reports in the mid 40’s to high 50’s. Yields in North Central and Northwest Oklahoma continue to range from the mid 40 to mid-60 bushels per acre depending on variety and location. In the Panhandle regions, irrigated wheat harvest continues. Yields on irrigated wheat in the central to the western regions of the Panhandle have not been as favorable as years past with a lot of irrigated wheat making 50 to 75 bushels per acre, with an occasional report of 100 bushels per acre or slightly higher. Test weights in the Panhandle continue steady at 60 lbs. to 62 lbs. per bushel. In some areas on the earlier harvested dryland wheat, test weights were a bit lower at 58 lbs. per bushel. Proteins across the state for this 2020 harvest have ranged from 8% to as high as 15.5%. The state average for protein is being reported between 11% to 11.2%.

This will be the last harvest report conducted by the Oklahoma Wheat Commission for the 2020 harvest season.

Oklahoma Wheat Harvest Moves Ahead but is Hindered by Rain in Most Regions Over the Weekend – Harvest Report June 22, 2020

Courtesy Oklahoma Wheat Commission

What is left of Oklahoma wheat harvest has been at a standstill in most places since Thursday night due to rain showers in the North Central and Northwest regions of Oklahoma. Rains have come thru off and on in all these areas the past 5 days, with the exceptions of Northeast Oklahoma in the Afton and Miami regions. Although they received light showers in parts of Northeast Oklahoma early this morning, producers were able to harvest in the Afton and Miami areas over the weekend.  Many of the acres in this region have gone into soybeans and other summer crops, so wheat harvest started and was finished over a period of 3 days. Combines were also slowed in all regions of the Panhandle over the weekend due to light rains on Friday night, but combines are back rolling in the Central Panhandle and Western Panhandle regions today.  Rains in the Eastern region of the Panhandle were heavier and producers will be at a standstill, although much of the wheat is already cut in this area.  Irrigated wheat in the central Panhandle around the Texhoma, Guymon and Hooker regions is ranging from the 60 bushels per acre to 90 bushels per acre depending on planting date, variety and location. Some higher yields have been reported with intensive management, but the severe drought and late freezes seem to have had an impact on both the dryland and irrigated crops. Dryland wheat harvest has finished in that area and with yields not too favorable making in the mid teens to mid 20’s. Proteins in the region from 11.9% to 14.9%.  Test weights on all wheat even with lower yields is still favorable ranging from 60 lbs. to 64 lbs. per bushel.  The Oklahoma Wheat Commission is calling Oklahoma Wheat Harvest 95% completed.


Texhoma/Guymon/Hooker – Much of the dryland wheat in this area has been utilized for other purposes due to the extreme drought conditions. Yields on irrigated wheat are reported at 60 bushels to 90 bushels per acre. Some higher yields over 100 have been reported on fields with intensive management practices.  Test weights are ranging from 61 lbs. to 66 lbs. per bushel. Proteins are ranging from 12% to 14.5%.  Harvest in this area is approximately 80% complete.

Boise CityHarvest is 60% complete.  Producers in this area were hindered from getting in the fields over the weekend due to rain, but combines are moving today.  For the most part, test weights on all wheat are favorable coming in at 60 lbs. to 63 lbs. per bushel. Protein is ranging from 11.0% to 14.9%. Yields on the dryland have been making in the mid teens to mid  20’s. Irrigated wheat is ranging from 50 bushels to 75 bushels per acre.

Northeast Oklahoma

Afton and Miami- Harvest is 99% complete.  Harvest started last Wednesday and producers in this region were able to get everything harvested over a 3 to 4 day period, before rains came into the region early Monday morning. Yields ranged from 20 to 40 bushels per acre and were much lower due to excessive moisture and late freezes.  Few wheat acres were harvested in this region due to producers putting a majority of acres into summer crops. Test weights were extremely favorable ranging from 61 lbs. to 62 lbs. per bushel even on the Soft Red Winter wheat that was harvested.  Soft Red Winter wheat test weights are usually much lighter but this year they managed to come in just as high as the Hard Red Winter wheat acres.  No proteins were reported. 

The next harvest report by the Oklahoma Wheat Commission will be published Wednesday, June 24, 2020.

Wheat Disease Update – 17 June 2020

This article was written by Dr. Bob Hunger, Extension Wheat Pathologist

I thought my 5-June update would be my last, but two samples/reports have come in that are prompting another update.  One of these reports was wheat kernels with darkened-colored germ ends with the dark discoloration moving toward the middle of the seed and into the crease.  This is indicative of black point (Figure 1; photo on the left), which is a discoloration of the seed (typically the germ end of the seed) resulting from either infection by a number of different fungi that typically are saprophytes (living on dead tissue) but can occasionally parasitize living tissue, or from a combination of abiotic (environmental) conditions that promote the discoloration without the presence of an organism.  Often black point occurs when freeze damage has occurred, or harvest was delayed and dead tissue in the heads has been heavily colonized by fungi that cause sooty mold (Figure 1; photo on the right).  Black point in wheat grain can be a grading factor as the discoloration can result in black flecks in flour milled from such grain.  Additionally, if used as seed wheat, kernels with black point can have reduce germination resulting in a lower seedling emergence.  Hence, if wheat showing black point is to be used as seed wheat, it is imperative to check the germination of that seed and to use a seed treatment that controls seed and seedling rots.

Figure 1. Wheat kernels with black point (photo on the left; note the pinkish color on the two outer wheat kernels, which is a seed treatment that had been applied), and sooty mold on a mature wheat head (photo on the right; photo credit – Dr. Erick DeWolf; Kansas State University)

 A second notable occurrence has been the report of wheat infested with common bunt/stinking smut.  This disease should not be confused with loose smut.  Loose smut is readily identified in the field as wheat is heading, and is characterized by heads with loose black spores (Figure 2; photo on the left).  There is a big difference between loose smut and common bunt/stinking smut.  Wind moves spores of the loose smut fungus to healthy wheat heads where they infect the developing seed at about the same time that flowering occurs.  Hence, the loose smut fungus is inside of that seed.  If the wheat is sold for flour there is no problem.  However, if that infected seed is used as seed wheat the next fall, then the loose smut fungus will grow within the seedling and plant that emerges from that infected seed.  Then at heading, instead of a normal head emerging a head filled with the black, loose smut spores emerges.  In contrast to loose smut, common bunt/stinking smut produces ‘bunt balls’ in wheat heads (Figure 2; middle photo and photo to the right), which break and spread spores onto healthy wheat kernels as well as into the soil in the field.  Hence, spores of the common bunt fungus survive on wheat kernels or in the soil and not inside of seed as is the case with loose smut.  In the fall when wheat germinates, the common bunt spores also germinate and infect the young seedling.  The fungus then grows with the plant, and as heading occurs and the wheat senesces, bunt balls are formed rather than wheat kernels.  Another difference between these two smuts is that no odor is associated with loose smut, whereas a strong musty/fishy odor is associated with common bunt, especially if there is a bad infestation.

Figure 2. Loose smut (left photo); common bunt/stinking smut bunt balls in a mature wheat head (middle photo; photo credit; Dr. Bill Bockus; Kansas State University); bunt balls of common bunt/stinking smut compared to healthy wheat kernels (right photo).

Recently I have received reports and a sample of wheat grain heavily infested with common bunt/stinking smut.  The wheat kernels appear to have blackened tips (Figure 3; top left and top right photos), but in contrast to black tip (Figure 1) where the germ end is darkened, in this case the brush end of the seed is darkened.  This blackening of the brush end is caused by thousands of common bunt/stinking smut spores being trapped in the brush (Figure 3; bottom photo).  I am bringing this to your attention because although both loose smut and common bunt/stinking smut can create significant problems, both are readily controlled by the use of an appropriate seed treatment.  Many such treatments are available.  Some are for insects, some are for bunts and smuts, some are for root rots, and many are for a combination of wheat insect pests and wheat diseases.  A good starting point as a guide for an appropriate seed treatment is the table on pages 262-263 in the 2020 OSU Extension Agents’ Handbook of Insect, Plant Disease, and Weed Control (OCES publication E-832) where many (but not all) of the more common seed treatments are listed.  It may not be necessary to plant treated wheat seed every year to manage loose smut and common bunt/stinking smut, but it is much better to manage them preventatively rather than wait until there is a severe outbreak of either one in a field.

Figure 3. Healthy wheat kernels covered with spores of the common bunt/stinking smut fungus (top two photos). Note the dark color at the top (brush end) of the kernels, which is due to the trapping of thousands of spores in the brush of the wheat kernel (bottom photo).