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Join me in congratulating Dr. Bob Hunger for his retirement after 39 years of service!
Amanda de Oliveira Silva, Small Grains Extension Specialist
Today I would like to dedicate a post to Dr. Bob Hunger, who has served as the OSU Wheat Extension Pathologist for 39 years and is officially retiring today!
Bob, I am grateful to have had the chance to work with you during our time at OSU. Thanks for being a mentor, colleague, and a friend. I know you have many fun plans, but I hope you won’t forget us.
I had so much fun traveling with you to field days this year. I learned many things with you, including a few American sayings like “bright-eyed and bushy-tailed” on our early morning trips and how to use a printed road map to get to our sites instead of using a GPS. However, I am not sure I will follow you on this last one lol.
Bob, I hope you know the great contributions you have made to the OK wheat industry and how much we appreciate you. See a few pictures below 🙂
Thank you, Bob!
Feel free to leave a message to Bob here below. I am sure he will be glad to read it.
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.
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.
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.
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).
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).
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.
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).
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).
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.
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.
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.
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 virus, High 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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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 .
If PREVENTABLE LOSS IS GREATER THAN CONTROL COSTS TREAT
IF PREVENTABLE LOSS IS LESS THAN CONTROL COSTS DON’T TREAT
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 – 30 March 2021
This article was written by Bob Hunger, Extension Wheat Pathologist
Reports of foliar diseases, especially stripe and leaf rust, are starting to increase in southern Texas and around Stillwater. First, here is an update sent out on 24-March by Dr. Amir Ibrahim (Regents Professor & Small Grains Breeder/Geneticist; Texas A&M AgriLife Research). Dr. Ibrahim is finding both stripe rust and leaf rust increasing across southern Texas.
“I visited our small grains trials at McGregor (18 miles southwest of Waco, TX) on March 18, 2021. Stripe rust (caused by P. striiformis Westend. f. sp. tritici Eriks.) continues to be active (Figure 1; photo on the left). Leaf rust (caused by Puccinia triticina Erikss.) is beginning to move to the middle canopy (Figure 1 – photo on the right).”
“We visited the naturally inoculated Rust Evaluation Nursery at Castroville, TX today. The nursery is about 196 miles from Texas A&M University’s main campus in College Station, where we are based. We also visited our trials at Uvalde, TX today. Stripe rust is not very active at both Castroville and Uvalde. Leaf rust is now picking up, especially at the Rust Evaluation Nursery at Castroville. Stripe rust is very actively spreading at the Agronomy Farm near our main campus in College Station as of our last visit on March 23, 2021. Stripe rust is also active in our trials in Greenville (50 miles northeast of Dallas). No reports yet of leaf or stripe rusts in the Texas High Plains. Leaf rust is also developing in our trials at Wharton (60 miles southwest of Houston).”
In Oklahoma, both stripe and leaf rust (Figure 2) have been observed in trials around Stillwater and near Perkins (about 15 miles south of Stillwater). Also recall in my update of 15-March, I indicated seeing powdery mildew, Septoria/Stagonospora (Figure 3) on lower leaves in many trials. These diseases also are present, and with the relatively cool and windy weather in the forecast, I expect the incidence and severity of all these diseases to increase.
First Hollow Stem Update – 3/17/2021
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 a dime) of stem below the developing grain head (see full explanation). The latest FHS results from OSU forage trials in Chickasha (Table 1) and Stillwater (Table 2) are listed below. For an additional resource, see the Mesonet First Hollow Stem Advisor.
We use an accelerated growth system to report the earliest onset of FHS stage. Trials are seeded early to simulate a grazed system, but the forage is not removed. Varieties reported here with the earliest FHS date should be the first to monitor in commercial fields. In practice, wheat that is grazed will likely reach FHS stage later than reported here, and differences between varieties will likely moderate.
Table 1. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/29/20 but not grazed or clipped. 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. Varieties exceeding the threshold are highlighted in red.
Table 2. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/21/20 but not grazed or clipped. 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. Varieties exceeding the threshold are highlighted in red.
- Additional resources available:
