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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Army Cutworms Reported in Some Wheat and Alfalfa Fields

This article was written by Tom Royer, Extension Entomologist and IPM Coordinator and Kelly Seuhs, Associate Extension Specialist.

Several people, including Lanie Hale, Rob Anderson, and Mike Rosen of Wheeler Brothers and Area Extension Agronomist Heath Sanders have reported possible army cutworm activity. These reports are based on direct observations and noticeable crow and blackbird “gatherings” in some wheat and alfalfa fields in areas of western Oklahoma. Infestation levels were at the “caution” stage at this time and caterpillars measured ¼ to ½ inches.

Army cutworms tolerate cold and feed throughout the winter months. Adult army cutworm moths migrate to Oklahoma each fall (August through October) from their grounds in the Rocky Mountains.  They seek bare or sparsely vegetated fields (like a newly prepared field ready for wheat planting, or a field that was “dusted in” and had not yet or just emerged, or a newly planted alfalfa stand). The eggs hatch soon after deposition.  A producer might see different sizes of larvae in a field due to the long migration period. Army cutworms feed throughout the winter and molt seven times before they turn into pupae in the soil.  Most larvae will have pupated by mid-late March. Adult moths begin emerging in April to fly back to the Rocky Mountains to spend the summer.

Army cutworms can severely damage wheat, canola, and newly planted stands of alfalfa if not controlled. Cutworm damage often goes unnoticed through much of the winter because the caterpillars grow slowly and don’t get big enough to cause noticeable damage until temperatures warm in the spring.  One early indication cutworm presence in a field is the gathering of blackbirds and or crows that seem to be actively feeding. It becomes important to check the fields for cutworms before they cause damage and stand loss.

Figure 1. Wheat stand loss from army cutworm. Figure 2. Cutworm damage to canola

Sample a field by stirring or digging the soil to a depth of two inches at five or more locations.  The cutworms will be “greenish grey”, and will probably curl up into a tight “C” when disturbed. 

It is better to control army cutworms when they are small (½ inch long or less). Army cutworms are very susceptible to pyrethroid insecticides. At this time of year, an insecticide application can be combined with a late winter top-dress nitrogen application.  Suggested treatment thresholds for army cutworms in wheat are 2-3 worms per row foot when conditions are dry and 4-5 per row foot if moisture is adequate. Current recommendations for army cutworm control in small grains are listed in CR-7194, Management of Insect and Mite Pests in Small Grains

It is better to control army cutworms when they are small (½ inch long or less). Army cutworms are very susceptible to pyrethroid insecticides. At this time of year, an insecticide application can be combined with a late winter top-dress nitrogen application.  Suggested treatment thresholds for army cutworms in wheat are 2-3 worms per row foot when conditions are dry and 4-5 per row foot if moisture is adequate. Current recommendations for army cutworm control in small grains are listed in CR-7194, Management of Insect and Mite Pests in Small Grains

The suggested treatment threshold for cutworms in canola is 1-2 per row-foot.  Current recommendations for control of army cutworms in canola are listed in CR-7667, Management of Insect and Mite Pests in Canola.

In newly seeded alfalfa, the threshold is 1-2 larvae per square foot. In established alfalfa fields, the threshold is 2-4 larvae per square foot and should be adjusted based on the size of the caterpillars (2-3 per square foot if caterpillars are more than ½ inches, 3-4 per square foot if less than ½ inches). Current recommendations for control of army cutworms in alfalfa are listed in CR-7150, Alfalfa Forage Insect Control.

Wheat Disease Update – 13/02/2020

This article was written by Bob Hunger, Extension Wheat Pathologist

This is an early season update to summarize a few items that have come up during this week. To start however, I need to repeat that this past fall and winter have been amazingly lacking in diseases. The Diagnostic Lab only received a few wheat samples during the fall, none of which were found to be associated with a pathogen/disease. Causes included low pH, nutrition, and/or environment. This lack of disease still seems to be the predominate scenario. Around Stillwater, I was not able to find any rust or powdery mildew in any of the trials I examined this week. Additionally, it appears as though foliar disease is absent in south Texas as well as indicated by Dr. Amir Ibrahim (Regents Professor, Small Grains Breeder/Geneticist, Texas A&M University, College Station, TX) who indicated to me that, “It has been really quiet here. We have not seen stripe or leaf rust so far. I doubt the former will be an issue this year since it has not established yet and it is already getting warmer. However, I expect to see heavier leaf rust in mid-April if it continues to be this warm.”

Hence, it appears that early season stripe rust and leaf rust should not be a major concern in Oklahoma. In contrast, leaf spot diseases (especially tan spot) should be watched for if you have wheat planted into wheat residue. Josh Anderson (Senior Research Associate, Noble Research Institute, Ardmore, OK) found tan spot in no-till wheat plots planted into wheat residue near Burneyville in far south-central OK (Figure 1). Tan spot can be damaging to seedling wheat especially when it occurs in emerging spring wheat in northern states. However, tan spot also can be damaging to winter wheat if infection is severe in the spring as plants are coming out of winter dormancy. Often an early season fungicide application is used to control not only tan spot but also early season stripe rust and powdery mildew. Such an early season application (late February/March) will not provide protection from leaf rust later in the season (April/early May). If you do have wheat planted into wheat residue, I highly recommend scouting for the presence of not only tan spot, but other early season foliar diseases such as Septoria and Stagonospora leaf spots, powdery mildew, and early season stripe rust. If any of these diseases are seen as severe in late February or March, applying an early application of a fungicide may be beneficial. Keep in mind however, that the timing for an early season fungicide application does not coincide with the optimum timing for top-dressing with fertilizer. If it is likely that two applications will be used, I recommend making the first application with a lower cost generic and reserve the second application for a higher priced premium fungicide. For a photo guide to wheat diseases, go to: http://dasnr22.dasnr.okstate.edu/docushare/dsweb/Get/Document-11682/E1024%20Wheat%20Disease%20Identification.pdf

Figure 1. Leaf spotting of wheat due to tan spot on wheat growing in a no-till field near Burneyville, OK. Notice the small, tan spot present in many of the lesions as indicated by the arrows. [Photo credit: Josh Anderson, Noble Research Institute, Ardmore, OK]

For more information on fungicide applications, see: CR-7668 (Foliar Fungicides and Wheat Production in Oklahoma) and PSS-2138 (Split versus Single applications of Fungicide to Control Foliar Wheat Diseases)

First Hollow Stem update – 2/5/2020

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 latest FHS results from our forage trials in Chickasha (Table 1) and Stillwater (Table 2) are listed below. Few wheat varieties at Chickasha and 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 09/19/19. 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 09/18/19. 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.

It is time to check for first hollow stem in wheat

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 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.

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 Chickasha are listed below (Table 1). None of the varieties are at FHS (all values are below 1.5 cm), but values are likely to change with current soil moisture conditions and warmer temperature predicted for the next couple days.

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.

Table 1. First hollow stem results for each variety collected at Chickasha on 01/30/20. Plots were planted on 09/19/19. The threshold target for FHS is 1.5 cm. The value of hollow stem for each variety represents the average of ten measurements.

Weed management for slow-developing winter wheat.

Amanda de Oliveira Silva, Small Grains Extension Specialist and Misha Manuchehri, Weed Extension Specialist

November has been cooler than normal and that has limited wheat growth across the state. Most of fields where wheat was planted earlier have the crown roots slowly developing and top growth is lower than expected. Many of these fields have very thin stands and will probably not have enough forage to feed the cattle. In many areas, planting was delayed due to either lack or excess of moisture. Most of fields that were planted late are at 1-2 leaf stage with seminal roots developing. Plants are showing signs of cold injury but should grow out of it well.

Slow developing wheat due to cold temperatures.
Photo taken on December 2, 2019 in Stillwater, OK by Amanda de O. Silva
Symptom of cold injury on wheat planted on November 4th, 2019.
Photo taken on December 6, 2019 at Kingfisher County by Amanda de O. Silva.

Fall or Spring Herbicide Application for a slow-developing wheat?

Moisture has been plentiful in many areas in Oklahoma this fall. As a result, several winter annual weeds have emerged. These weeds are competing well with our wheat crop, which is behind in many areas due to cold temperatures. If you are investing in a herbicide application this year, you may be thinking “when should I apply”? The answer is not always simple but there are several things to consider before making this decision.

A 2019 winter wheat field heavily infested with Italian ryegrass.
Photo taken by Misha Manuchehri.
Henbit seedlings in a November 2019 planted wheat field in Stillwater.
Photo taken by Misha Manuchehri.

1. Is your wheat at an approved growth stage per the herbicide label?

Many postemergence herbicides labelled for use in wheat recommend the crop be at 2 or 3 leaves. Be sure to check these requirements to ensure crop safety.

2. What are your target weeds?

Many producers chose to apply a postemergence herbicide in the spring when top-dressing N to limit the number of passes made across their fields. This often makes sense for weeds that have multiple flushes, as two applications often are not financially feasible. For example, Italian ryegrass that is not managed with a delayed preemergence herbicide (Anthem Flex, Axiom, or Zidua) may be sprayed in the late winter vs. fall to target multiple flushes. On the other hand, early emerging, difficult-to-control grasses like rescuegrass, are best managed in the fall before entering “dormancy”.

3. What are daytime temperatures like? Are your wheat and weeds actively growing?

All postemergence herbicides labelled in wheat move in living tissue. Herbicide application will be most successful when your wheat AND your weeds are actively growing.

4. Have you applied this product before? Was it successful at that timing?

We can learn a lot from field history. If a product wasn’t successful in the past, we need to learn why so that we can make the necessary changes to increase its success or perhaps it is time to use a new weed management method. Finally, selection for herbicide resistant weed biotypes can occur quickly. If you are unsure if you have resistance, please send in a seed sample to the weed science lab.

It is time to scout wheat fields for fall armyworm!

By Amanda de Oliveira Silva, OSU Small Grains Extension Specialist and Tom Royer, Extension Entomologist

We are receiving reports of fall armyworms infestations and wanted to alert producers to check their wheat fields every day after seeding emergence. The worms can be very tiny and difficult to see it. Symptoms like “window pane” in the leaves indicate feeding from fall armyworm. Also, check under crop residue as they might try to hide from the heat.

Symptom of “window paned” leaves shows severe feeding from the fall armyworm. Photo taken on October 2, 2019 at Canadian County by Amanda de O. Silva.
Fall armyworms may be found under crop residue during the day. Photo taken on October 2, 2019 at Canadian County by Amanda de O. Silva.

Replanting decisions need to be made on field by field basis. Replanting might be best for producers taking the crop to a grain-only system. Also, allow some time to replant to avoid having infestations back again.

“We will not get relief from fall armyworms until we get a killing frost, so keep vigilant!” Tom Royer

Several helpful resources are available for producers. Contact your local county Extension office. For additional read refer to Pest e-alerts Reports of Seedling wheat Infested with Fall Armyworm 2019. Consult the newly updated OSU Fact Sheets CR-7193 Management of Insect Pests in Rangeland and Pasture and CR-7194 Management of Insect and Mite Pests of Small Grains for control suggestions.

Follow-up to “What can I expect from wheat just now emerging?”

By: David Marburger, former OSU Small Grains Extension Specialist


Wheat that was dusted-in or late-planted during the fall 2017 and resulted in spotty stands or no stands at all from a lack of soil moisture was a frustrating and common occurrence for many Oklahoma producers. Unfortunately, the first water some wheat seed imbibed did not occur until after a late-February rainfall. When the remaining seed started germinating and emerging, many were begging the question, “What is a realistic expectation for this late-emerging wheat crop?” In a March 2018 blog article titled, What can I expect from wheat just now emerging? I tried addressing several related questions:

  • Will these plants produce a head?
  • How cold and for how long do the seedlings need to be exposed to cooler temperatures to vernalize?
  • Is vernalization completely temperature dependent?
  • Do we have information on varietal differences?
  • What forage or grain yield potential do I have?


I also mentioned in that article that we were working on gathering more variety-specific information. We had a small, unused space next to the variety demonstration plots at the Stillwater agronomy farm. In that small space we were able to plant more than 30 varieties that were entered in the OSU variety trials last season (Figure 1). These plots were established on March 6 and managed similarly to the “grain-only” demonstration plots located immediately to the north of this area. The “grain-only” demonstration plots were established on October 31, 2017 with a seeding rate of 60 lbs/acre. In-furrow DAP at 50 lbs/acre was also applied. Therefore, the intention was for the planting date to be the only difference.

figure 1

Figure 1. Planting wheat on March 6, 2018 at the Stillwater agronomy farm.


figure 2

Figure 2. Picture taken on April 26, 2018 of the wheat varieties planted 51 days earlier. The “dual-purpose” and “grain-only” variety demonstration trials are those located to the right of this area. Every wheat variety entered into the variety trials (n = 56) was planted on September 19, 2017 to represent a dual-purpose planting date (background) and on October 31, 2017 to represent a grain-only planting date (foreground).


figure 3 top

figure 3 bottom

Figure 3. Photos taken on May 16, 2018. The top photo shows the progress of the wheat varieties planted on March 6, 2018. The bottom photo shows the area where the same varieties were planted on October 31, 2017. You can see how some of the varieties in the bottom photo are beginning to “turn.”


figure 4

Figure 4. Photo taken on June 9, 2018. Some of the varieties planted on March 6, 2018 produced heads while others did not. The right side of the photo shows a few of the varieties from the dual-purpose demonstration trial that were a few days from being harvest-ready.


figure 5

Figure 5. Photo taken on June 21, 2018. This shows the differences in the number of heads produced or lack thereof among varieties planted on March 6, 2018. Varieties within both planting date demonstration trials to the right were harvest-ready for some time by this date.


What did we find?

In the previous blog article, I mentioned that variety-specific vernalization requirements are not fully characterized, but winter wheat varieties adapted to the southern Great Plains may need between 120 to 1080 hours (5 to 43 days) at air temperatures below 45° F to vernalize. Dr. Brett Carver feels three weeks (504 hours) of exposure to constant temperatures below 45° F should be sufficient for most varieties in Oklahoma, but reducing that to two weeks (336 hours) may cause vernalization issues for some varieties.


After this demo was established, we experienced a cool March and April overall. In fact, April 2018 ended up being the second coldest on record. Hourly weather data provided by Wes Lee from the Stillwater Mesonet station showed that we accumulated 368 hours after March 6 where the average air temperature was less than 45° F. The last calendar day which had at least one hour with an average temperature below 45° F was April 28.


As a result of these conditions, we found 28 of 35 varieties (80%) produced heads. The heading dates for those varieties are provided in Table 1. For the 28 varieties which produced heads, we collected samples from the plots planted on March 6, 2018 and October 31, 2017 in order to make comparisons for a few plant characteristics. Two subsamples were collected from each plot within both planting dates. Each subsample consisted of 1 m of row. Plant height, head number, total biomass, total grain weight, harvest index, and seed weight were measured from each subsample. The data for each plant characteristic was averaged from the two subsamples within each planting date, and the results are presented in Tables 1 and 2.


table 1


table 2


Results Summary

  • 28 of 35 varieties (80%) produced heads to some level. The varieties which did not produce heads were Doublestop CL Plus, Duster, Iba, Joe, Showdown, Stardust, and TAM 114.
  • Compared to the same varieties planted on October 31, 2017, the 28 varieties which produced heads and were planted on March 6, 2018 on average:
    • headed 40 days later (range of 28 to 50 days later);
    • were 36% shorter in plant height (range of -20% to -48%);
    • produced 49% less number of heads (range of -17% to -78%);
    • produced 76% less total biomass (range of -47% to -93%);
    • produced 80% less total grain weight (range of -49% to -98%);
    • had reduced seed weight per 50 seeds by 39% (range of -16% to -58%);
    • had reduced harvest index by 24% (range of +44% to -70%)


Other Observations

A couple producers also shared some of their findings from late-emerging fields. Fred Schmedt near Altus, OK mentioned that some of their Bentley and Smith’s Gold which was planted into cotton stubble and emerged in the first week of March did produce grain. The yields they had were pretty similar to those for the same varieties in our demonstration. Jimmy Kinder near Walters, OK also had some Bentley which produced grain, and his yield was slightly better than yield for Bentley in our demonstration.


As a comparison to Stillwater, Wes Lee also provided me the hourly weather data from the Altus and Walters Mesonet stations. The number of accumulated hours beginning after March 6 where the average air temperature for the hour was below 45° F was 277 for Altus and 245 for Walters. The true number of accumulated hours though depended on the time when the seed of these varieties in these fields imbibed water and sprouted.



Final Thoughts

Hopefully Oklahoma winter wheat producers will never run into this problem again, and we can just put these data on the shelf to collect dust. If it does happen again though, these observations can at least give us a starting point to help aid in making more confident and timely decisions on how to move forward. However, it does not look good for forage or grain yield potential any way you slice it (as likely expected), and contacting your agent if you have crop insurance to discuss your options is highly advised. Also keep in mind that these results are from one location in one year under the cultural practices used. Seeding rate is an example of how cultural practices may influence the results. Using a higher seeding rate in attempt to compensate for less tiller production in a late-planted wheat scenario may not reduce total biomass and grain yield as dramatically compared to the observations in our demonstration.


Planting Date and Seeding Rate Considerations for Winter Wheat

With this August setting up similar to last year and the need for wheat pasture for a number of producers this fall, we will likely see drills start rolling in parts of the state by the end of the month. As planting gets going, here are a couple considerations when it comes to planting dates and seeding rates for Oklahoma winter wheat.


Planting date:

The optimal window for dual-purpose wheat for most of Oklahoma is between September 10-20 (approximately day 260 in Figure 1). This window represents a trade-off between maximizing forage production while minimizing potential grain yield loss. Earlier planting dates, last week into this week for example, will provide more fall forage potential, but this is usually not recommended unless the wheat is intended to be produced for grazing, or “grazeout.” Planting dates for grain-only producers will be at least 2-3 weeks later than what is the ideal dual-purpose planting date for your area. For many areas in Oklahoma, this will be around mid-October (approximately day 285 in Figure 1).

Fig1 planting date

Figure 1. Forage and grain yield potential in relation to the day of the year. Every 1,000 kg/ha is equal to approximately 900 lb/acre or 15 bu/acre. Ideal planting dates for dual-purpose wheat in Oklahoma are mid-September (i.e., approximately day 260). Planting for grain-only should occur at least 2-3 weeks after dual-purpose planting (i.e., mid-October or approximately day 285).


Seeding rate:

Producers in forage-only or dual-purpose management should plant 1.5-2x the amount of seed that is recommended for grain-only production. For example, data collected in north-central Oklahoma has showed that increasing the seeding rate from 60 to 120 lb/acre can increase fall forage potential by as much as 500 lb/acre for a mid-September planting date (September 11 in Figure 2). The increase in forage potential by using this higher seeding rate can justify the cost of the extra seed. OSU recommends 120 lb seed/acre for most areas of Oklahoma, including irrigated fields in the Panhandle. Seeding rates for dryland fields in the Panhandle for this type of management can be lowered to 90 lb/acre. OSU recommends a 60 lb/acre seeding rate for grain-only production when planted during that optimal mid-October time. Dryland fields in the Panhandle can have their seeding rate lowered to 45 lb/acre. If planting happens to get delayed in November this year, seeding rates will need to increase to provide enough available tillers to still maintain maximum grain yield potential.

Fig2 seeding rate

Figure 2. Fall forage yield collected in north-central Oklahoma as affected by seeding rate and planting date. Source: PSS-2178.


More information about dual-purpose wheat management can be found in the fact sheet PSS-2178 Dual-purpose Wheat: Management for Forage and Grain Production.

Disease and Insect Considerations to Make Before Planting Wheat This Fall

This article was written by Dr. Bob Hunger, Extension Wheat Pathologist, & Dr. Tom Royer, Extension Entomologist, Department of Entomology & Plant Pathology Oklahoma State University


Planting date: Much of the winter wheat in Oklahoma is sown with the intent of being 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://wheat.okstate.edu/wheat-management/seeding/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 (also called wheat mosaic), and Triticum mosaic (TrM). 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, 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 in 2017 compared to 2018.  In 2017, 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 were positive for one or both of these viruses. For a number of reasons, the planting date of wheat across Oklahoma in the fall of 2017 was significantly later than the fall of 2016. I believe this helped to lower incidence and severity of the mite-transmitted viruses in Oklahoma in 2018 compared to 2017.


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://wheat.okstate.edu/wheat-management/diseasesinsects/EPP-7328%20three%20virus%20diseases%20of%20wheat.pdf.



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 (e.g., Duster, Billings, Gallagher, Iba, Bentley, Tatanka, and Winterhawk) tolerate BYD better than other varieties; however, be aware that no wheat variety has a high level of resistance to the aphid/BYD complex. 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.


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. Some wheat varieties are either resistant (e.g., Duster, Gallagher, SY Flint, and LCS Wizard) or partially resistant [e.g., LCS Chrome, Everest, Ruby Lee (at cooler temperatures)] to Hessian fly infestations. 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 fly fall infestations, 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://wheat.okstate.edu/wheat-management/diseasesinsects/EPP7086hessianflyinoklahoma.pdf.


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) (Figure 6). During the late spring of 2016 and 2017, several samples of wheat were received that were diagnosed as being affected by take all and other root rots. In 2017-2018, the incidence and severity of root rots across Oklahoma dramatically increased. This increase likely resulted from weather conditions that favored the root rots. Dryland (Fusarium) root rot was the most common root rot observed, and caused significant damage to wheat in southwestern, western, northwestern OK as well as the panhandle.


Controlling root and foot rots is difficult. There are no resistant varieties, and although fungicide seed treatments with activity toward the root and foot rots are available, 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).


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 and flag smut spores carryover on seed or in the soil, loose smut carries over in the seed. Seed treatments are highly effective in controlling all the bunts/smuts. 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 is strongly recommended. If either common bunt 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 and loose smut is strongly recommended. For more information on common bunt & loose smut, see: http://www.entoplp.okstate.edu/ddd/hosts/wheat.htm and consult the “2017 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.


2017-2018 Oklahoma Wheat Crop Overview

At the time of writing this report, 2018 Oklahoma wheat production is estimated to be 52.0 million bushels, which is 47% less than the 2017 production (Table 1) and 62% less than the 2016 production. The lower total grain production is the result of less wheat acres harvested across the state, primarily from abandonment due to drought or baled for hay, and the below-average yield. The 4.3 million planted acres was only down 4% compared to the previous year, but that was still 18% lower than the previous ten-year average. Number of harvested acres is estimated at 2.0 million, which is 31% less than in 2017 (Table 1), and the lowest number in the state since 1913. The statewide average yield is projected at 26 bu/ac. This is 8 bu/ac (24%) less than the 2017 state average and 3.6 bu/ac (12%) less than the previous ten-year average.

table 1

The 2017-2018 wheat growing season was a fight from start to finish for many producers across the state. The growing season got an early start due to an unusual August for Oklahoma. Temperatures were below normal, and rainfall totals were above normal for the month. This prompted producers interested in targeting fall forage to begin planting at the end of August. Planting continued to move rapidly through the Labor Day weekend, and most of the wheat during this time was sown into adequate soil moisture and emerged rapidly. Those producers who waited until after Labor Day to plant saw more unfavorable conditions as temperatures rose, and available soil moisture quickly dried up. Wheat planted during this time was “dusted-in” and finally received precipitation toward the end of the month into the beginning of October to get the seed to germinate. Wheat planting intended for grain-only was stalled during the average timeframe of early to mid-October due to these precipitation events. Once the ground dried enough, most producers were able to quickly make up time and get the crop planted, but some needed until November to finish.


After mid-October, the rain quit falling for the remainder of the calendar year. Crop conditions during the early part of the season were average but quickly deteriorated as the season progressed. This also led to a disappointing fall forage production and grazing season for most producers. Those who planted during late August to early September and were able to protect the crop from fall armyworm achieved good stands and had some available pasture later in the fall. However, those who waited until after Labor Day or later to plant were not as fortunate. The later planting and lack of precipitation resulted in low total fall forage production or no available pasture at all.


Drought conditions and average to below average temperatures persisted throughout January into February. Even for the producers who had available fall pasture, the drought conditions limited the overall number of days of grazing.


Some precipitation finally fell in parts of the state during late February into early March. For many fields, this was the first precipitation received since planting. Below average temperatures were observed coming out of winter, and plants broke winter dormancy later than normal. Below average temperatures persisted, resulting in slow overall growth and development during this time. The first hollow stem growth stage was reached for many varieties during the second to third week of March, which was 7 to 10 days later than normal. Unfortunately, the rain received during late February to early March was not quite enough to give any grazed wheat the boost it needed to recover well.


Overall growth and development continued at a slower than normal pace due to the second coldest April on record. Three separate and widespread freeze events also occurred during the first week of April, resulting in significant injury in some areas. Most wheat headed during mid- to late April because of the cooler temperatures, with this being 7 to 14 days behind normal. The prevailing thought was that this would translate into a later than normal harvest. However, the cold temperatures in April were followed by the warmest May on record. The warm temperatures and lack of rainfall advanced the crop quickly at this point, resulting in suboptimal conditions for the grain-fill period.


Most wheat was mature in southwestern Oklahoma by the end of May and by the beginning of June in the central to northern parts of the state. Producers for the most part were not delayed by rainfall events, and with the dry weather during June, much of the wheat was harvested timely and quickly.


Overall, harvest was almost complete in the state by late June. Yields throughout Oklahoma were variable depending on location but were below average overall. Part of this variability was due to overgrazing and whether an area caught or missed a rainfall event during early spring. Field averages of 15 to 30 bu/ac were the norm across much of the state, but higher averages, even into the 50 to 60 bu/ac range, were not uncommon in some areas that received timely rainfall. Test weights throughout harvest remained at or above 60 lb/bu for early-harvested fields and did not drop much below the upper 50’s towards the end of harvest. Protein content also remained at or above acceptable levels.


Different insects were a concern at times during the growing season, but few were widespread or season-long outside of the fall armyworm. Unless treated, the fall armyworm devastated those producers who planted in late August into early September. Many fields had to be replanted, and some producers commented that this was the worst that they had ever observed. Unfortunately, some reports indicated the fall armyworm was still causing damage into early November. The dry weather experienced across the state through the winter provided ideal conditions for winter grain mite and brown wheat mite to thrive on wheat plants coming out of winter dormancy, and there were some reports of fields warranting control. Aphids were not really on the radar screen of most producers until mid-March, but this pest was still not the limiting factor as observed in other years. Despite the low aphid numbers, Barley Yellow Dwarf (BYD) was evident in some fields as flag leaves and heads started to emerge. While there was quite a bit of leaf purpling and yellowing associated with BYD, there was not much stunting observed, with stunting resulting from “hot spots” of aphid pressure with early-season transmission of the virus. Wheat Streak Mosaic (WSM), transmitted by the wheat curl mite, was an issue again for producers in southwestern Oklahoma, but the overall impact of WSM was not as much as the 2016-2017 crop season. Reasons for this were related to later planting and emergence of some wheat; additionally, fields which may have had WSM were abandoned due to the drought or cut and baled for hay before symptoms could be observed.


Diseases were at low levels overall during the season, primarily due to the drought conditions. Parts of central to southcentral Oklahoma did experience low levels of powdery mildew, leaf rust, and stripe rust. In some cases, powdery mildew could be observed high in the canopy. For the remainder of the state, it was difficult to find foliar diseases, especially during stem elongation into the grain-fill period. One disease more prominent than in years past was Fusarium foot dry (dryland root rot). Signs and symptoms of this disease appeared suddenly during early May as hot temperatures returned and as the crop progressed through grain-fill. However, symptoms of this disease can appear similar to symptoms of premature death caused by freeze, drought, and other conditions. In parts of the northwest and panhandle regions, symptoms of dryland root rot may have been confused with symptoms caused by the drought and/or freeze, whereas in others (such as the wheat variety trial at Lahoma), damage caused by the April freeze events was expressed distinctly earlier. Because of the impact that leaf rust and stripe rust have had over the past several years, producers were ready to apply a foliar fungicide to susceptible varieties, but unfavorable conditions for disease development did not warrant an application in most cases. Variety trial results from Apache and Lahoma indicated that producers in these areas were justified in not spraying, as no evidence of a positive response to a fungicide application was found. However at Chickasha where low to medium levels of leaf and stripe rust and medium to high levels of powdery mildew were present, the two fungicide applications implemented at this location contributed to protecting the yield potential for a number of varieties compared to the non-treated plots of those same varieties.