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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Oklahoma Wheat Harvest Begins for the 2021 Season, Amid Cooler Temperatures and Heavy Moisture

Courtesy Oklahoma Wheat Commission

The 2021 wheat harvest has begun with several locations in Southwest, Oklahoma, reporting a successful weekend for grain being received.  The following counties that received grain in elevator locations were Harmon, Jackson, Tillman, Cotton, Comanche, Kiowa and Greer.  A few reports of sample loads being accepted in Frederick on Saturday, May 29th. Rain showers across Southwestern, Oklahoma, over the Memorial Day weekend hindered producers from making any progress over this past week until Saturday, June 5th.  During this period, cooler temperatures, cloud cover and high moisture levels on the grain have slowed progress on harvesting the crop.   Traditionally combines are rolling in Southwest, Oklahoma Memorial Day weekend or before, but unseasonable cool temperatures and rain has delayed the crop maturing.  High quality and favorable test weights have been noted so far.   Rains across Southwest, Oklahoma, late last night and early this morning have put harvest on standstill again in several regions, while in other areas producers hope to get rolling again later this afternoon, west of Tillman and Kiowa counties.  In a large area of Tillman county, producers are reporting 3 to 5 inch rains last night, which will delay harvest another 4 to 5 days.  Regions of Cotton and Comanche county locations received 1/10th to 2.5 inches of moisture depending on location.

Overall early wheat that has been harvested in Southwest, Oklahoma, indicates strong quality and decent yields. Yields reported varied depending on locations and producer management.  Test weights are averaging 60 lbs./bu. or higher.  While it is premature to report on protein, early numbers are ranging between 11 and 12 percent.

Grandfield/Devol- Harvest started over the weekend, although moisture last night will make it a late start today. More moisture was reported around Grandfield with less rain in the Devol area where combines will likely start up again.   Test weights for this region being reported at 60 +.  Yields around Grandfield and Devol have been favorable ranging from 40 to 50 bushels per acre.   One field has been reported at 70 bushels per acre.

Frederick/Chattanooga- The past two days have been successful for harvest in this region, but heavy rains last night across Tillman County is going to hinder harvest most likely another 4 to 5 days depending on the location.  Three to five inch rains from elevator managers in this region being reported today.  Areas of heavy rain did not report on Mesonet due to the nature of pop- up storms. Test weights ranging from 60 to 61 lbs./bu. Yields in this region not being reported as favorable as Comanche County but still ranging from the high 30’s on heavily grazed wheat to the mid 40’s on early cuttings.

Altus/Duke- Harvest was successful in this region over the weekend, while light moisture and humidity will most likely hinder harvest in Altus.  Little rain was received out at Duke so producers are hopeful combines in this area as well as in Harmon and Greer Counties will move later today. Note: much of the wheat in Harmon and Greer counties was cut for hay due to the excessive ongoing drought in this region.  Test weights in this area being reported at 61 to 62 lbs./bu.  Yields being reported from high 30’s to mid 60’s on fields with extremely progressive management systems.

Lone Wolf/Hobart-Producers also had success with harvesting in this region over the past two days.  Light rains and higher humidity will likely hinder an early start to harvest today in most places, certain regions may be delayed longer from getting into the fields in Kiowa county.  Test weights in this region averaging 62.4 lbs./bu. Yields being reported from the mid 30’s to mid 50’s depending on location and management.

Sentinel/Rocky- While it was close to starting this weekend at these locations, light rains today will most likely hinder harvest another couple days in this area.  No wheat was reported as taken in at these locations over the weekend.

Enclosed, see the 14-Day and 12-Hour rainfall accumulation maps with the 7-day weather forecast for Oklahoma.

The next harvest report by the Oklahoma Wheat Commission will be published Wednesday, June 9, 2021.

Wheat Disease Update – 21 May 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

Wheat tours over the last ten days included Kingfisher (Kingfisher County; south central OK), Cherokee (Alfalfa County; north central OK), Alva (Woods County; northwestern OK), Lahoma (Garfield County; north central OK), Morris (Okmulgee County; eastern OK), El Reno (Canadian County; central OK); and Buffalo (Harper County; northwestern OK).  Wheat in these areas is pretty much done with flowering and kernels ranged from just forming to fully formed.  Some varieties in some areas were in the milk stage with some approaching soft dough.

      Diseases at these locations varied considerably but overall, a wider range of diseases was observed.  Some locations such as Cherokee, Alva and Buffalo had relatively light foliar disease incidence with some leaves indicating barley yellow dwarf and wheat streak mosaic (and/or other mite transmitted viruses).  Around Stillwater and at Lahoma, although stripe rust was still prevalent leaf rust is making an appearance (Figure 1).  At others such as Kingfisher, Morris and El Reno, leaf rust could be found but stripe rust seemed to still be more prevalent.  Leaf spot diseases also were observed at most of these locations, but these foliar diseases were not as prevalent as the rusts.

Figure 1. Stripe and leaf rust both observed on wheat at Lahoma on May 13/14. A mixture of stripe and leaf rust (photo on left) compared to mostly all leaf rust (middle and right photos). [Photo credits – Dr. Amanda de Oliveira Silva; OSU Small Grains Agronomist].

Darkened heads were observed at several locations but were most prominent and prevalent at Morris in eastern OK (Figure 2).  Darkened heads like this can result from several causes.  If Septoria and/or Stagonospora are present on lower leaves, these fungi can move up onto the heads and cause a glume blotch that has this appearance.  Another possibility is a bacterial disease called black chaff or bacterial streak (Figure 3).  Black chaff will occur on leaves (Figure 3; photo on left), but also can move onto heads (Figure 3; center photo).  Note on this center photo how the stem (peduncle) immediately beneath the head shows darkened lesions like those on the head.  Finally, awns of heads infected with black chaff often show an alternating pattern of dark and white (Figure 3; photo on right).  Another possible cause of these dark heads is presence of a gene that confers resistance to wheat stem rust.  In this case, the result is not a disease, but rather an association with the presence of that gene.  Regarding the darkened heads observed in the trial near Morris, Dr. Silva and I agree it is most likely the majority of the darkened heads observed likely resulted from freeze damage as many of these heads also were totally or partially sterile (see Dr. Silva’s blog at https://osuwheat.com/2021/05/18/freeze-damage-update/).  However, Septoria/Stagonospora and black chaff also contributed as symptoms of these diseases were observed in the field.

Figure 2. Darkened heads observed on wheat heads in a trial located in eastern Oklahoma near Morris. These darkened heads were caused by Septoria/Stagonospora, black chaff and/or freeze. [Photo credits – Dr. Amanda de Oliveira Silva; OSU Small Grains Agronomist].
Figure 3. Black chaff (bacterial streak) on wheat at Chickasha in 2013. Photo on the left is of a leaf infection; center photo shows darkening of the head and the stem just beneath the head; photo on the right shows the alternating dark and light pattern often seen on awns of wheat heads infected with the bacterium that causes black chaff. [Photo credits: Dr. Jeff Edwards; Oklahoma State University]

A final disease observed this past week was indicated by the sporadic occurrence of white heads in some parts of the field.  Examination of plants/tillers associated with these white/yellowing heads revealed symptoms typical of take all root rot (Figure 4).  However, I am not yet certain that these tillers had take all as symptoms of other root rots also were present.  Hence, samples were brought back to the lab for isolation and identification.  Look for an update on this in my next report but be aware there likely will be root rot showing up in some areas of the state.

Figure 4. Symptoms of take all root rot. White heads (photo on left) as the plants mature often indicate presence of a root rot. Lower, blackened stems and crowns of tillers with white heads resulting from take all root rot (photo on the right).

This next week marks the end of the wheat field days in Oklahoma with four coming next Thursday and Friday in the Oklahoma panhandle.  A complete schedule of the remaining field days can be viewed at: http://wheat.okstate.edu/virtual-plot-tour/2021OSUWheatFieldTours.pdf

Freeze damage update

Amanda de Oliveira Silva, Small Grains Extension Specialist

It has been almost one month since the freeze event on April 21, and we are now obtaining a better picture of potential freeze damage on wheat fields across Oklahoma. As I have indicated, the extent of the freeze damage will depend on several factors, including the growth stage of the plants, how low the temperature will get, and how long it stays at those cold temperatures. Wheat growth stage ranged from flag leaf emergence to heads starting to or fully emerged when the freeze occurred, and number of hours and temperature varied across the state (Figure 1).

Figure 1. Hour below freezing two days after the freeze event.

Traveling around the state for plot tours these past weeks, I have seen and heard about damage ranging from minimal to quite severe. Some fields seem to be fine with only scattered damaged heads and the grain appears to be filling as expected. Other fields however, show much more significant damage with discolored and sterile heads.

At the plot tour at Chickasha on April 30, there was a mix of freeze and hail damage with several abnormally growing heads (due to head trapping). Anthers seemed to be fine at that point (Figure 2).

Figure 2. Abnormally growing wheat heads at the Chickasha variety trial on April 30.

On May 7, I checked some wheat fields around Sentinel with Gary Strickland (Jackson County Extension Educator and SW Regional Agronomist) and we observed almost no freeze damage with a few heads in the field showing a pale color and partial sterility (Figure 3). I have observed this symptom commonly in fields I have visited, and many producers have described this to me as well.  Although common, it typically has been found at a low incidence.

Figure 3. Freeze damaged heads with partial sterility and pale color near Sentinel, OK on May 7.

We observed a few spots with freeze damage while at Alva on May 12, especially in low spots of the field and on the tops of terraces. Again, relatively few spots in the field showed damage. The wheat was looking good at Alva, but really needing a rain (Figure 4).

Figure 4. Freeze damage on wheat in low spots of the field at Alva, May 12.

The most severe freeze damage that I have seen so far was yesterday near Morris in eastern OK. The heads were green but there was no grain present (i.e. sterile). Damaged heads had glumes with a chocolate discoloration, which is similar to the discoloration caused by the bacterial disease called black chaff. In some cases, Dr. Hunger and I felt these discolored heads were the result of this bacterial disease but that the majority of the heads showing these symptoms were the result of freeze damage (Figure 5).

Figure 5. Freeze damaged heads without grains inside and showing a chocolate color on the outside (top photos). Heads showing no freeze damage and black chaff bacterial disease (bottom photos).

At the plot tour at El Reno today, we also observed a few varieties with pale colored and “empty” heads due to the freeze (Figure 6). We observed more freeze damage on wheat that was planted earlier and grazed as compared to the grain-only (ungrazed) wheat in that same field. Another noteworthy item is related to my earlier observation that the February freeze hurt some of the varieties in the dual-purpose plots by severely reducing tillering that would cause a loss of stand. That observation in those varieties was confirmed as the stand loss was quite evident today.

Figure 6. Wheat at El Reno. Same variety under grain-only (left) and dual-purpose (right) systems.

In conclusion, the freeze damage I am seeing is variable within and across fields, but overall I would say is minimal in most of the state. However, continue to keep scouting as it will now be easier to identify freeze damage.

Please let me know what you are seeing out there! My email is silvaa@okstate.edu.

Also, contact your County Extension office for more information.

Lahoma Field Day is this Friday – May 14!

Are you planning to attend the in-person event?

Please pre-register here: http://wheat.okstate.edu/plot-tours/21EXT_Lahoma_eFlyer_altFINAL.pdf

The program will start a little earlier at around 8:45am and the presentations will start at 9:15am. 

Are you planning to watch it online? 

Please see below the livestream link for each presentation. All you need to do is to click on the link at the time of each talk.

9:15 am – Wheat Varieties – Amanda Silva, Small Grains Extension Specialist

10:00 am – Integrated Weed Management – Misha Manuchehri, Weed Science Extension Specialist

10:45 am – Wheat Breeding and Disease Update – Brett Carver, Wheat Breeder and Bob Hunger, Extension Wheat Pathologist

All of these will be available live at www.youtube.com/sunuptv

For more information go here: http://wheat.okstate.edu/plot-tours/21EXT_Lahoma_eFlyer_altFINAL.pdf

Looking forward to seeing you there!

Wheat Disease Update – 10 May 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

Wheat tours last week included Homestead (Blaine County; west-central OK), Afton (Ottawa County; northeastern OK), Sentinel and Tipton (Washita and Tillman Counties, respectively; southwestern OK) and Kildare and Lamont (Kay and Grant Counties, respectively; north-central OK).  At Homestead, Dr. Amanda Silva (OSU Small Grains Agronomist) saw primarily tan spot (Figure 1) as this trial was planted in a field of wheat after wheat.  Sentinel was fairly free of foliar diseases, but the trial at Tipton was severely infected with stripe rust.  The incidence and severity of stripe rust at Tipton also was observed by Dr. Brett Carver (OSU Wheat Breeder/Geneticist) who indicated that he saw severe stripe rust in his trials at Tipton as well.  Near Chattanooga OK, also in SW OK, there was a report of stripe rust occurring in wheat heads (Figure 1, center photo and photo to the right).  Over the years, I have occasionally observed this in Oklahoma, and it typically is a signal that stripe rust has been severe.  As far as I know, the grain is not infected, but rather it is the plant tissue surrounding the grain.  These reports of severe stripe rust contrast with what Dr. Silva and I observed at Afton, Kildare, and Lamont where little foliar disease of any type was observed.  We did however see symptoms indicative of barley yellow dwarf at all locations and some indicative of the mite-transmitted virus diseases such as wheat streak mosaic and high plains disease.

Figure 1. Tan spot (photo on left) observed on May 3rd by Dr. Amanda Silva (OSU Small Grains Agronomist) in the variety trial at Homestead, OK in west-central OK. Center and photo to the right show stripe rust that has infected and is sporulating in a wheat head. The photo credit for these two photos goes to Leon Fisher and came to me via Jerry Goodson and Mike Schulz (Station Supt, Altus).

This week will be spent at wheat field days in central, north central, and northwestern OK including trials near Cherokee, Kingfisher, Thomas, Alva, and Lahoma. A complete schedule of the remaining field days can be viewed at: http://wheat.okstate.edu/virtual-plot-tour/2021OSUWheatFieldTours.pdf

Wheat Disease Update – 4 May 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

Wheat tours last week to Walters (Cotton County) in south-central OK, Altus (Jackson County) in southwestern OK, and Apache and Chickasha (both in Caddo County) in central OK showed wheat in these areas to be either quickly approaching flowering, at flowering, or just past flowering.  In all locations except Altus, stripe rust was by far the most prevalent foliar disease.  At Altus, there simply has not been sufficient moisture for any foliar disease to develop.  At the other locations, stripe rust was light at Walters, light to moderate at Apache, and moderate to severe at Chickasha.  Stripe rust in trials around Stillwater also has increased significantly as shown in Figure 1.  Although some leaf spotting and powdery mildew occasionally was observed on lower leaves, these diseases were at a low incidence and severity.

Figure 1. Severe stripe rust in a susceptible wheat line at Stillwater, OK on 5-1-2021.

Other diseases observed included barley yellow dwarf, which was present at all locations but did not seem to occur over large areas.  Another disease observed at a low incidence was loose smut (Figure 2; left photo; credit Mike Schulte).  If you recall, last year there was a higher than typical occurrence of loose smut across Oklahoma and although present again this year, loose smut seems to be more sporadic and at a lower incidence compared to 2020.  Another disease that we did not see at these southern OK field days was wheat streak mosaic virus (Figure 2; right photo).  However, we continue to receive a steady number of samples that are testing positive for Wheat streak mosaic virusHigh plains virus, or both.  These samples are coming from northern to northwestern OK and the panhandle, and it appears that mite transmitted virus diseases such as wheat streak mosaic and high plains virus will be a significant factor in certain fields in 2021.

Figure 2. A loose smutted head observed in southern Oklahoma the last week of April 2021 (left photo; photo credit: Mike Schulte) and wheat showing symptoms from a co-infection of Wheat streak mosaic virus plus High plains virus (right photo; photo credit Dr. Charlie Rush, Texas A&M University).

Finally, this week will be spent at wheat field days in northeastern OK (Afton) and in north-central OK (Kildare and Lamont). A complete schedule of those field days can be viewed at: http://wheat.okstate.edu/virtual-plot-tour/2021OSUWheatFieldTours.pdf

Wheat Disease Update – 23 April 2021

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

      Just a brief update to relay that stripe rust continues to increase across Oklahoma.  Bryan Vincent (Crop Consultant; north-central OK) reported severe stripe rust in “hot spots” on an unknown variety just north of Lamont, OK (Grant County) close to the Kansas border (Figure 1; left photo). In Major County, which is immediately south of Grant County, Josh Coltrain (Winter Wheat Technical Development Lead, Syngenta) reported he had, “found quite high incidence of stripe rust” in Syngenta’s plots near Carrier, OK.  Here around Stillwater, I have observed severe stripe rust in spreader strips of the susceptible variety Pete. These infections stood out because of resistant breeder lines planted immediately adjacent to the strips of Pete (Figure 1; center photo and photo to the right).

Figure 1. Severe stripe rust in a susceptible variety (Pete) planted next to resistant breeder lines in a nursery at Stillwater, OK (photo on the left). The photo on the right shows the severity of stripe rust pustules on an individual leaf of Pete.

      However, the most striking example I have seen of stripe rust in some time was observed by Jeff Wright (Coordinator of Production Operations; OFSS; Oklahoma State University) in an increase field of the old variety Triumph 64 near Perkins (about 15 miles south of Stillwater).  As you can see in Figure 2 (two top photos), much of the entire field (9 acres) appears yellowish.  Examination of leaves reveals severe stripe rust infection associated with yellowing of the leaf (middle photo). The bottom photo in Figure 2 is of Jeff’s tractor after applying a fungicide.  Although the fungicide should protect the green leaves remaining in the field, much of the leaf tissue will be killed from the stripe rust infection.  This is a good example of the importance of applying a fungicide to a susceptible variety sufficiently early to prevent such widespread infection. What and how such a big and uniform infection occurred is puzzling to me, but I suspect that is related to overwintering of the stripe rust fungus in the field.

Figure 2. Severe leaf rust on Triumph 64 wheat near Perkins, OK (about 20 miles south of Stillwater, OK). Top two photos show the yellowish cast to the foliage. The middle photo shows stripe rust pustules associated with severe chlorosis (yellowing) of the foliage. The bottom photo shows Jeff’s tractor after applying a fungicide spray two days ago.

      In other wheat around Stillwater, there continues to be a high incidence and severity of powdery mildew.  Barley yellow dwarf also is easily found in many trials and varieties.  Dr. Tom Royer has sent out an alert about finding English grain aphids around the state.  These aphids also were observed by Bryan Vincent in north-central OK and by me here around Stillwater. Finally, the wheat field days start next week, so observations from those locations will start to appear in subsequent updates. A complete schedule of those field days can be viewed at: http://wheat.okstate.edu/Home/plot-tours/

Assessing potential freeze damage on wheat

Amanda de Oliveira Silva, Small Grains Extension Specialist

Temperatures dropped below freezing in the past hours in northwestern Oklahoma and Panhandle (Figures 1 and 2), and freezing temperatures are expected across most of the state tomorrow morning (April 21) (Figure 3). There is a potential for freeze injury to Oklahoma wheat. The extent of that will depend on several factors, including the growth stage of the plants, how low the temperature will get, and how long it stays at those cold temperatures.

Figure 1. Minimum air temperature (in Fahrenheit) over the past 24 hours at each Mesonet station. Figure courtesy Oklahoma Mesonet.
Figure 2. Number of hours spent at or below freezing (32°F) over the past 48 hours at Mesonet station. Figure courtesy Oklahoma Mesonet.
Figure 3. Freezing temperatures are predicted for most of Oklahoma on Wednesday morning, April 21, 2021. Figure courtesy Oklahoma Mesonet, Weather Forecast Office.

What are the temperatures that can damage the wheat plants?

This will depend on the growth stage of the plants. Anecdotal evidence suggests varietal differences in resistance to spring freeze injury, but this is likely due to differences in plant growth stages when the freeze event occurred. Earlier maturing varieties are more likely to be injured from these recent freeze events than later maturing varieties because they are likely more advanced. The susceptibility of wheat plants to freeze injury steadily increases as we progress through the spring from jointing to heading and flowering. Figure 4 below is 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. It is difficult to have exact numbers because each freeze event is unique. While a field at the jointing stage could spend two hours at 24 F, it is possible that the same amount of injury could occur at a 28 F temperature that was sustained for a more extended period.

Figure 4. Temperatures that can cause injury to winter wheat at different growth stages. Source: Kansas State University publication C646: Spring Freeze Injury to Kansas Wheat.

How long should I wait to assess the injury?

Another important thing to keep in mind is that we need to be patient before assessing freeze injury. The extent of a significant freeze event may not be apparent 1 or 2 days after. If warm temperatures return quickly, you should wait about 5-7 days before determining the injury. Suppose temperatures remain cool after the freeze event. In that case, it may take 10-14 days before the extent of the injury can be fully assessed.

What are some freeze injury symptoms to look for?

A typical freeze injury symptom is leaf tips turning yellow and necrotic (Figure 5). This is very often just cosmetic and will not hurt yield in the end. More severe damage can result in the entire leaf turning yellow to white, and the plants become flaccid (Figure 6). You may even notice a “silage” smell after several days.

Figure 5. 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 6. 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.

The most important plant part to check is the developing head (i.e., growing point)

This will be important for areas of the state with fields with plants at flag leaf emergence stage. Sometimes we can see what look like healthy plants overall, but the developing head has been damaged or killed. To get a look at the developing head, you can slice the stem open lengthways. A healthy growing point will have a crisp, whitish-green appearance and be turgid (Figure 7). Often, you can lightly flick the head, and if it bounces back and does not break, it is still healthy. If it is mushy, limp, and breaks or parts of it break off when you lightly flick it, it has been compromised. It may also have a brown color (Figure 8, right). Another indication that the growing point has been compromised is that the next emerging leaf is necrotic, and the lower stems are discolored, with lesions and enlarged nodes.

Figure 7. Close up of a healthy wheat head (growing point) above the second node with whitish-green color and turgid.
Figure 8. Plants that appear healthy could have damaged heads. The photo on the left shows a healthy head, and the photo on the right shows a freeze-damaged head.

Freezing at the boot stage may cause the head to be trapped by the sheaths of the flag leaf resulting in issues with head emergence (Figure 9). The whitish tips of the awns indicate that it was exposed to freezing temperatures and that the flower parts could have been compromised. Freeze during the flowering stage may result in flower sterility via the death of the anthers (male organ) and consequently poor kernel set and grain yield losses (Figure 10).

Also, the percent of damaged heads may not translate into percent yield loss. For example, there is still an opportunity for wheat to produce additional tillers and/or retain secondary tillers at the jointing stage. Whether or not these tillers can compensate for larger tillers that were lost due to freeze will depend on the subsequent weather. If conditions are favorable, there is a chance for late-emerging tillers to have a shot at producing grain. If the wheat is more advanced (which is the case for most Oklahoma wheat), it will be more challenging to make this type of recovery.

Figure 9. Freeze at the boot stage may cause the head to be trapped in the boot and not being able to emerge properly.
Figure 10. Freeze during the flowering stage may result in sterility via death of the anthers (male organ) and consequently poor kernel set and grain yield losses.

A few points to consider:

Every freeze event is unique and freeze injury needs to be checked on a field by field basis – the temperatures and time durations we use regarding freeze injury are rules of thumb and are not exact. I have seen instances where conventional wisdom would indicate complete crop loss, and we skate through with minimal damage.

The amount of injury observed will depend on – the growth stage of the plants, how low the temperature got, and how long it stayed at those cold temperatures. Other factors such as elevation, residue cover, and moisture can influence the observed temperature within the canopy as well. Because of the number of influential factors, it is important to check each field. It is possible to have variability in injury symptoms among fields and even within fields.

It will take a few days to see how bad things are – Symptoms may start to appear mid-next week and will likely be identifiable by the end of the following week. Healthy wheat heads will remain turgid with a green color. Damaged wheat heads will be bleached, yellow, or brown and will easily break when pushed against.

Additional Resources

Contact your local Extension office.

C646: Spring Freeze Injury to Kansas Wheat.

Aphids: Bird Cherry-Oat Aphids and an Invasion by the “English” (Grain Aphid that is) and Armyworms: Decisions……

This article was written by Dr. Tom A. Royer, Extension Entomologist

The good news is that Oklahoma has a healthy, good-looking wheat crop. Now, it must be protected from any swarming hordes of insect pests that want to eat it!  Dr. Kris Giles has been surveying wheat fields in SW and Central Oklahoma. I have been collecting data from our wheat plots in Chickasha, Stillwater, and Lahoma. Dr. Giles found increasing bird cherry oat aphid (BCOA) numbers, and its main natural enemy (Lysiphlebus testaceipes) may have been set back by the record cold temperatures that we experienced in February. I have seen mixed populations of English grain aphids and bird cherry oat aphis in our wheat plots.

Sometimes, aphid infestations are overlooked. Bird cherry-oat aphid infestations do not produce visible damage until they become very numerous and English grain aphids often bury themselves in between the seeds where they blend in. So check your field for bird cherry oat aphid, English grain aphids. 
Bird cherry oat aphids are olive green to dark green with two rusty patches that surround their “tailpipes” (cornicles).  They feed on plant juices with their piercing sucking mouthparts. They can reproduce rapidly, so fields should be scouted to make a determination as to the need to control them.                                                                                   

Lady beetles and most importantly, the Lysiphlebus wasp that parasitizes them, often control bird cherry oat aphids.  Parasitized aphids swell up and form “mummies” that can easily be seen (below).  If an aphid infestation has 10-15% mummies, the rest are probably also parasitized.     

BCOA and aphid mummy

English grain aphid is larger than either greenbug or bird cherry oat aphid (0.125 inches), green with long black cornicles and legs that have alternate bands of green and black. Their appearance is sometimes characterized as “spidery”. Suggested thresholds are 5 per stem at flag leaf, and 10 per stem at head emergence through milk stage.

English Grain Aphids in a wheat head

My suggestion is to scout the field beforehand to determine if there are GROWING numbers of bird cherry oat aphids that could be or are of concern.  Count bird cherry oat aphids on each of 25 randomly selected tillers across a zigzag transect of the field and note mummy activity. If 10 to 20% of bird-cherry oat aphids are mummies, and there are numerous lady beetle larvae in the wheat, consider control.  If wheat heads have emerged, look for English grain aphids imbedded in the head.

Unpublished research provided by Dr. Kris Giles (OSU) and Dr. Norm Elliott (USDA-ARS) combined with studies on spring wheat from the Dakotas and Minnesota indicate that 20-40 BCOA per tiller causes 5-9% yield loss before wheat reaches the boot stage.  My suggestions: if BCOA numbers average 10-20 per tiller, figure on a 5% loss, if 20-40 per tiller, figure a 7% loss, and if BCOA aphids are more than 40 per tiller, figure a 9% loss.

Estimate APHIDS PER TILLER_______ /tiller =       Total # aphids ______/25 tillers

Estimate CROP VALUE $_______/acre =                 Expected yield ______bushels/acre X $ _____/bushel

Calculate CONTROL COSTS $______/acre =           Insecticide $______/acre + Application $____/Acre 

PREVENTABLE LOSS $_____/acre = Crop value $________ X______loss from aphids/tiller .   



Here is a Table of Preventable Loss estimates for bird cherry-oat aphids for expected yields of 30 to 50 bushels per acre, expected wheat prices of $3.00, $3.50, and $4.00 per bushel, and bird cherry-oat aphid numbers of 10-20, 20 to 40, and over 40 per tiller.

This cool, rainy spring weather, while providing excellent growing conditions for wheat, is also foodstuff for “producing” armyworms. Armyworm infestations typically occur in late April through the first two weeks of May. They feed on leaves and awns, (below left) and occasionally clip the head from developing plants. The head clipping (below right) I have noticed over the years is mostly restricted to secondary tillers with very small, green heads that contribute very little to yield.

Since armyworm infestations tend to occur more frequently around waterways, areas of lush growth, or areas with lodged plants, check them first to determine the size of the infestation. Early signs of an infestation include chewed leaves with ragged margins.  You may find “frass” i.e. the excrement from armyworm caterpillars, around the base of wheat stems and clipped heads.  Also, look for evidence of armyworms parasitized by the wasp Glyptapanteles militaris. This parasitoid attacks armyworms as well as several other caterpillars. When the larva emerges, it produces a cottony cocoon (below right) about the size of a Q-tip. Scout for armyworms at five or more locations looking for “curled up worms” (below left)

Armyworm caterpillars tend to feed at night, so another good strategy is to bring a flashlight, shine it on the emerged wheat heads after dusk and count armyworms that are feeding on the heads and plant stems. 

The suggested treatment threshold for armyworms is 4-5 caterpillars per linear foot of row (bottom left). Generally, no control is needed if wheat is past the soft dough stage unless there is visible head clipping, and caterpillars are present and feeding.

If a producer is considering a fungicide application, this might be an opportune time to evaluate your field for bird cherry oat aphid, English grain aphid and/or armyworms. If NEEDED, combine an insecticide with a needed fungicide application to control multiple pests.  Check CR-7194, “Management of Insect and Mite Pests in Small Grains” for registered insecticides, application rates, and grazing/harvest waiting periods.  It can be obtained from any Oklahoma County Extension Office, or found at the OSU Extra Website at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2601/CR-7194web2008.pdf

Wheat Disease Update – 14 April 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

      Last week (08-April) in southwestern OK, Gary Strickland (Jackson County Extn Educator) reported seeing only very little stripe rust, but that tan spot was still present in the lower canopy.  Southwestern OK has been hot and dry, so conditions in that part of Oklahoma have not been at all favorable for foliar disease development.  Also last week, Bryan Vincent (Crop Consultant; north-central OK) reported seeing mostly tan spot and powdery mildew across northern OK, with little to no rust, but some barley yellow dwarf starting to appear as well as aphids.  Greg Highfill (Woods County Extn Educator) also reported heavy tan spot in a no-till, wheat- after-wheat field.

      More recently, although still scattered and light, both leaf and stripe rust (more so stripe) appears to be increasing across Oklahoma.  Lanie Hale (Manager, Wheeler Brothers) sent out the following report.  “Yesterday, Will Bedwell and I scouted 22 wheat fields in southern Major, northeastern Dewey, and northwestern Blaine Counties.  The wheat variety was unknown to us in most of the fields.  In seven of the fields, we found leaf and/or stripe rust in isolated areas, certainly not widespread across the fields.  We found powdery mildew in a few fields, but only where the canopy was heavy and dense.  Septoria and/or Tan Spot was noted on lower leaves in most fields.  Many of the fields had infestations of Bird Cherry Oat Aphids ranging from light to moderately heavy.  We saw several Lady Beetles and larvae in fields; I only saw one mummified aphid indicating not many parasitic wasps are present.  One of the fields had been sprayed over the weekend.  The flag leaf is emerging in most fields we scouted.  We did not scout any field with 100% emerged flag leaves.”

      Yesterday around Stillwater, I saw wheat that ranged from flag leaves emerging to wheat headed, although by far and away most of the wheat was at the boot/pre-boot stage (GS 9 or so).  By far, the most prevalent disease I observed was powdery mildew (Figure 1).  Stripe rust also was present, but at a low incidence.  I also noted quite a few spots or patches of barley yellow dwarf in various trials, but in contrast to other reports, I saw very few aphids.

      Given these reports and observations, it is advisable for producers to start watching their fields closely and prepare for applying a fungicide, especially if growing a variety susceptible to either rust and/or the other foliar diseases.  For more information on fungicides and their use, see OSU CR-7668, which can be found at:  https://extension.okstate.edu/fact-sheets/foliar-fungicides-and-wheat-production-in-oklahoma-march-2016.html.

Figure 1. Wheat leaves observed near Stillwater, OK on 4-13-2021 with powdery mildew and stripe rust (top photo) and with stripe rust (bottom photo).

Perhaps the most striking observation is that wheat streak mosaic (Figure 2) is starting to be reported across both Oklahoma and Texas as a couple of samples have tested positive for Wheat streak mosaic virus in the last week.  For more information on this and other mite-transmitted viruses, please see OSU EPP 7328 that can be accessed at:  https://extension.okstate.edu/fact-sheets/wheat-streak-mosaic-high-plains-disease-and-triticum-mosaic-three-virus-diseases-of-wheat-in-oklahoma.html

Figure 2. Wheat streak mosaic virus has been observed in northwestern Oklahoma and western Texas.