Considerations to Make before Planting Wheat this Fall
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 during the late fall through 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 such as mite-transmitted viruses, the aphid/barley yellow dwarf complex, and root and foot rots will be more prevalent and more 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:
Mite-transmitted virus diseases. These include wheat streak mosaic (WSM), wheat mosaic (formerly called high plains disease), and Triticum mosaic (TrM). All are transmitted by wheat curl mite (WCMs). WCMs and these viruses survive in crops such as wheat and corn, 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. In the spring of 2016, several fields of commercial wheat in north-central and northwestern OK were destroyed by WSM. These fields were growing immediately adjacent to fields left fallow during the fall/winter of 2015-2016. The fallow fields contained abundant volunteer wheat and grassy weeds from which WCMs carrying WSMV spread into the commercial fields. Wheat infected in the fall is either killed by the next spring or will be severely damaged. Hence, it is imperative to be a good neighbor and control volunteer wheat and grassy weeds in fields left fallow – especially, if they are adjacent to commercial wheat fields.
A commercial wheat field showing severe symptoms of wheat streak mosaic (left). The commercial field was infested during the fall and winter with wheat curl mites carrying the virus from volunteer wheat and grassy weeds that were not controlled in the fallow field. The picture on the right are typical foliar symptoms of WSM.
Seed treatments are not effective in controlling these mite-transmitted virus diseases. However, planting later in the fall (after October 1 in northern OK and after October 15 in southern OK) and controlling volunteer wheat are two practices that provide some control. 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, destroying volunteer wheat at least two weeks prior to emergence of seedling wheat will greatly reduce mite numbers in the fall. In addition to these cultural controls, two winter wheat varieties (RonL from Kansas and Mace from Nebraska) have resistance to WSM; however, their adaptation to production is limited to northwestern Oklahoma. For more information on mite-transmitted virus diseases, see OSU Fact Sheet 7328 (Wheat Streak Mosaic, High Plains Disease and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) at: http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-8987/EPP-7328.pdf
Aphid/barley yellow dwarf (BYD) complex: Viruses that cause BYD are transmitted by many cereal-feeding aphids. 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, Endurance, Gallagher, Iba, Doublestop CL+, Bentley, Everest, Winterhawk, Redhawk) 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 virus(es) that cause BYD. Systemic seed-treatment insecticides including Gaucho (imidacloprid) and Cruiser (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.
Spot in field (top) of barley yellow dwarf (BYD) as would be seen in March or April. Many types of aphids (for example, greenbug; bottom) transmit the viruses that cause BYD.
Hessian fly: Hessian fly infestations occur in the fall and spring. Fall infestations arise from over-summering pupae that emerge when climate conditions become favorable.
Adult Hessian fly (left) and larvae and pupae of the Hessian fly (right)
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-Southwind, LCS Wizard, Winterhawk) or partially resistant (e.g. Everest, Iba, Jackpot, PostRock, Ruby Lee, SY-Gold, T-153, Tam 304, WB-Stout) 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:
Root and foot rots: These include several diseases caused by fungi such as dryland (Fusarium) root rot, Rhizoctonia root rot (sharp eyespot), common root rot, take-all, and eyespot (strawbreaker). Be aware that in the late spring of 2016, several samples of wheat were received that were diagnosed as being affected by take all and other root rots. This could indicate a greater incidence of wheat root rots in 2017, but the incidence and severity of root rots is highly dependent on weather conditions so it is impossible to predict their incidence and severity this early.
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).
White heads indicative of root rot (left); darkened roots (right) indicative of root rot (in this case, take all).
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 “2016 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.
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.
This is article is authored by Dr. David Marburger, Dr. Jeff Edwards, Dr. Brett Carver, Robert Calhoun, Dr. Tracy Beedy, and Dr. Bob Hunger
As of right now, the 2015-2016 Oklahoma wheat production is estimated to be approximately 132 million bushels, which is about 34% greater than our 2015 production (Table 1) and 277% greater than production in 2014. Although the estimated harvested acres is lower than 2015, the statewide average yield is projected at 40 bu/ac, and this is a 14 bu/ac (54%) increase compared to 2015 (Table 1). Based on these projections, this would be the largest wheat production since 2012, but the average yield would be a new state record.
|Table 1. Oklahoma wheat production for 2015 and 2016 as estimated by USDA NASS, July 2016|
|Harvested Acres||3.7 million||3.3 million|
|Total bushels||98.8 million||132 million|
The 2015-2016 wheat growing season was unlike most years in Oklahoma, characterized by periods of plentiful rainfall and near optimal growing conditions at critical times. Most wheat was sown into soil with adequate moisture, allowing it to emerge rapidly. The sufficient rainfall and mild temperatures allowed for good fall growth and bumper forage yields. In fact, plants in many non-grazed fields were abnormally large and phenologically advanced going into winter, and there was some concern about winter-kill. With mild temperatures continuing into the winter months, this concern proved to be largely unfounded, and most plants moved to spring green-up without injury.
Similar to 2014 and 2015, January and February were dry months for the Southern Great Plains, and the ample forage growth quickly wicked moisture from the soil. As the wheat crop was coming out of dormancy, there was much concern that the dry conditions would quickly reduce yield potential. Fortunately, rain fell during early- to mid-March as the crop was greening up. This also helped provide grazed wheat the extra boost it needed to recover from grazing injury.
As the wheat crop progressed from green-up to flowering, rain continued to fall, but warmer than normal temperatures moved the crop along quickly, and at the time, most thought harvest would come earlier than normal. As we transitioned into grain fill, temperatures stayed at more ideal levels, favoring kernel filling.
Most wheat was mature in southwestern Oklahoma and in the central part of the state by the end of the May. Widespread rainfall at the end of May delayed most producers from beginning harvest until the first week in June. Dry weather during June allowed much of the wheat crop to be harvested quickly. Unfortunately, some areas of southwestern Oklahoma were plagued by regular and heavy rainfall events that delayed harvest towards the end of the month. Overall, harvest was pretty well wrapped up in the state by the end of June.
Yields throughout Oklahoma were very good overall, with field averages of 30 to 60 bu/ac being the norm. Field averages in the 60 to 90 bu/ac range were not uncommon, and there were even isolated cases of fields averaging over 100 bu/ac. Some producers expressed they will never see their yields this high again in their lifetime, and let’s hope they are wrong! 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. This was a much welcomed change from the low test weights of 2015.
Other than bird cherry oat aphids and wheat curl mites, there were few widespread insect problems in 2015-2016. Aphids were not really on the radar screen of most producers until numbers ballooned in mid-March. As a result, it was not hard to find Barley Yellow Dwarf (BYD) as flag leaves and heads started to emerge. While there was quite a bit of purpling associated with BYD, there was not as much stunting as sometimes observed with early-season transmission of the virus. Wheat Streak Mosaic (WSM) was not as wide spread as in 2015, but it was still a significant issue for many producers in 2016. The favorable growing conditions likely reduced the impact of both BYD and WSM, and yield reductions were not as severe as they might have been in a more drought stressed environment.
Similar to 2015, stripe rust was the major foliar disease impacting wheat production in 2016. The devastation caused by the 2015 stripe rust epidemic had many producers more open to the idea of foliar fungicide application to susceptible varieties. Many fields throughout the state received at least one fungicide application, and anecdotal evidence from agricultural retailers indicates that Oklahoma wheat acres treated with a foliar fungicide in 2016 was more than double that treated in 2015. Variety trial results from Apache, Chickasha, and Lahoma indicate that producers were well justified in spraying many of these acres. Grain yield of the popular variety Ruby Lee, for example, was increased by 68 bu/ac at Chickasha when treated twice with a foliar fungicide. Our results at Chickasha also show the power of genetic resistance to disease in varieties such as Billings which maintained an 83 bu/ac grain yield without the assistance of a foliar fungicide. In addition to stripe rust, leaf rust was present, but it was at low levels in isolated areas and was not widespread throughout the state.
For information regarding the 2015-2016 OSU Wheat Performance Trials, visit the home page of wheat.okstate.edu. Yield results from all individual locations, as well as a two-page summary of all locations, are posted. For those of you also also interested in the fall forage variety trial information, you can find that here: http://wheat.okstate.edu/variety-testing/forage-yield.
This article is written by Dr. Bob Hunger, Extension Wheat Pathologist.
Department of Entomology & Plant Pathology – 127 Noble Research Center
Oklahoma State University – Stillwater, OK
405-744-9958 (work) – firstname.lastname@example.org
This likely will be my last OK disease update for a while as diseases have mostly “run their course” in Oklahoma and harvest has started. However, I wanted to provide a follow-up on the late season root rots we saw at several locations across northern Oklahoma. Symptoms and a description of the setting in the field all pointed to take-all in several of the samples, and Jen Olson in the Diagnostic Lab and I did find visual signs of the take-all fungus. With further examination, Jen found lesions indicative of Rhizoctonia root rot, and subsequently, she isolatedRhizoctonia. In another sample with whiteheads that to me appeared to be take all, Jen isolated Parastagonospora nodorum and Fusarium (most likely acuminatum as indicated by DNA sequencing). In a third sample in which roots appeared clean but the lower stems were discolored, Jen isolated Rhizoctonia, but also more commonly Fusarium (again most likely acuminatum), Curvularia, and Parastagonospora. Likely some of these were secondary. So, the exact cause of the whiteheads is somewhat uncertain with Rhizoctonia root rot, take-all, and perhaps some Fusarium-induced root rot all involved.
Reports/excerpts of reports from other states: Just to let you know, stripe rust appears to be a major disease up through the northern Great Plains and into the mid-east as indicated below. In many of these states, producers are facing the dilemma of needing two sprays – one to control early season stripe rust and another at flowering to help suppress Fusarium head blight (scab). We faced a similar dilemma here in Oklahoma but with an early application to control early season stripe rust and then perhaps a later one to control later season foliar diseases and or scab (in eastern/north-eastern OK). All with low wheat prices, but without the fungicide yield and quality (test weight) would be hurt as with what happened last year.
North Dakota: Dr. Andrew Friskop (Ast Professor/Cereal Extn Pathologist); North Dakota State University; May 23, 2016: “Stripe rust was confirmed in two counties in North Dakota on May 23. One sample was from a winter wheat research plot near Fargo (Cass County), and the other was from a winter wheat variety performance trial in southwest ND near Hettinger (Adams Co.). This is approximately 10 days ahead of when stripe rust was detected in North Dakota last year. Given the susceptibility in popular spring wheat and winter wheat varieties, growers will be encouraged to scout especially with rain and dew in the forecast.”
Ohio: Dr. Pierce Paul (Aso Professor); Ohio State University; May 24, 2016: “Stripe rust continues to spread across the state of Ohio. This is the most widespread and the earliest I have seen this disease in the state in 13 years. Several varieties in fields south of interstate 70 and west of interstate 71 are severely affected, with substantial damage to the flag leaf well before flowering in multiple hot spots in some field. As we approach flowering in more northern counties, the reports continue to come in. Several fields have already been sprayed for stripe rust, but the dilemma facing most growers is whether to spray for stripe rust or wait to spray for scab in fields not yet at anthesis.”
Severe stripe rust in Ohio – Dr. Pierce Paul
South Dakota: Dr. Emmanuel Byamukama (Ast Professor/Extn Spec – Plant Pathology); South Dakota State University; May 27, 2016: “I scouted several winter wheat fields this week in East (Codington, Clark) , Central (Beadle, Hyde, Hand, Hughes) and West (Stanley, Jackson, Pennington) South Dakota and I found stripe rust in almost every field I scouted. The majority of these fields have stripe rust just starting while a few have moderate to severe stripe rust. Winter wheat is beginning to head and a few fields are at flowering. With more rain in the forecast, a fungicide may be necessary to manage stripe rust. The challenge is going to be needing another fungicide shortly for scab management. And with the wheat prices not encouraging, producers are concerned applying 2-3 fungicides in winter wheat this season.”
Severe stripe rust in South Dakota – Dr. Emmanuel Byamukama
Article written by Dr. Bob Hunger, Extension Wheat Pathologist
Department of Entomology & Plant Pathology – 127 Noble Research Center – Oklahoma State University – Stillwater, OK
405-744-9958 (work) – email@example.com
This past week (Monday & Tuesday) I visited the Dr. Raymond Sidwell Station near Lahoma (Major County), and the variety trials near Cherokee (Alfalfa County) and Alva (Woods County) on my way to field days in the panhandle near Balko and Hooker (Texas and Beaver Counties). Except for in the panhandle, wheat foliage is pretty much done for in Oklahoma. Wheat in the panhandle was mostly in the kernel forming stage. Diseases observed on the trip to the panhandle included stripe rust (some still actively sporulating), wheat streak mosaic/high plains, and barley yellow dwarf. Samples submitted to the Plant Disease and Insect Diagnostic Lab also have tested positive for these viruses. As indicated in the 14-May update, take-all/root rot has been confirmed from a couple samples received from across central and northern Oklahoma. Take-all has been confirmed, but it appears another root rot also may be involved. Jen Olson in the PDIDL is making isolations to help resolve exactly what is involved in terms of root rot disease. In south-central Oklahoma Aaron Henson (Tillman County Extn Educator) indicated to me that wheat is variable in maturity but he estimates that some harvesting should begin in 1.5 to 2 weeks. Heath Sanders (Area Extn Agron Spclt located in southwestern OK) indicated much the same – especially if the cool/wet weather becomes more seasonally hot and dry.
Reports/excerpts of reports from other states:
Cereal Rust Bulletin from the Cereal Disease Lab in Minnesota; May 18, 2016: Highlights/reports in the Cereal Rust Bulletin include:
· Wheat stem rust was found in a nursery in south central Georgia.
· Wheat stripe is widespread in the U.S., now reported in 24 states.
· Oat crown rust has now been reported in Texas, Louisiana, Mississippi, Alabama and North Carolina.
The link to this report is: http://www.ars.usda.gov/SP2UserFiles/ad_hoc/36400500Cerealrustbulletins/16CRB4.pdf
Kansas: Dr. Erick De Wolf (Extn Plant Pathologist); Kansas State University; May 18, 2016: “Wheat in central and south central Kansas is at the grain filling stages of growth with many fields at or near the milk stages of kernel development. Stripe rust is severe in many fields that were not treated with fungicides this year. Fields of susceptible varieties have stripe rust severity >80% on flag leaves in demonstration plots in Pratt, Kingman, Harper, Barber counties. The disease was also severe in Ellsworth county were a fungicide demonstration plot had nearly 100% severity of the flag leaves. The weather this week appears highly conducive for continued disease development and the risk of severe disease appears to be high in Northwestern and West Central KS where low levels of stripe rust have been reported on the flag leaves. Varieties with genetic resistance are performing well with disease reactions very similar to what we saw in previous years. To date, T-158, Gallagher, WB-Grainfield, TAM 114, WB Cedar, Sy- Monument have all had moderate levels of resistance to the disease. This suggests that the race structure of the stripe rust fungus is similar to last year. Low levels of leaf rust were observed in Kingman, Pratt, Barber and Harper Counties.”
“We can think of nothing more suitable than to have our new Dr. Raymond Sidwell Research Facility’s grand opening be part of our May 13 Wheat Field Day, as Raymond worked diligently for decades to make the annual field day one of the premier agricultural events in the Southern Plains,” said Tom Coon, OSU vice president for agricultural programs.
Sidwell served as senior station manager for the 143-acre experiment station, located in the heart of wheat production country near Lahoma, from June of 1980 until his passing in December of 2013.
“We invite everyone to join us as we honor Dr. Sidwell and showcase the importance of crop research being conducted through our statewide Oklahoma Agricultural Experiment Station system,” Coon said. “Lahoma is situated on Highway 60 just west of Enid, for those who have never been to the experiment station. Signs will be posted.”
There is no cost to attend the 2016 Wheat Field Day, which will take place from 8:30 a.m. to approximately noon. Lunch will be provided free of charge thanks to the generosity of several sponsors.
Richard Austin, current station superintendent, said the state-of-the-art Dr. Raymond Sidwell Research Facility has a conference room, offices and restrooms compliant with the Americans with Disabilities Act, and features a large open bay design that will facilitate equipment and make possible field day events unimpeded by weather.
“There is a lot of orange integrated into the building, signifying it is an OSU facility, which everyone who knew Raymond recognizes would be important to him,” Austin said.
In addition, Sidwell was known to be fond of porches, so one was incorporated into the front of the facility.
“It’s a nice touch people can enjoy, allowing those who visit the facility to be outside but out of the sun and hopefully remember what Raymond meant to Oklahoma agricultural producers and agribusinesses,” said Randy Raper, OAES assistant director.
More than three decades of Sidwell’s meticulous management of the station allowed for major research efforts in wheat breeding and variety development, soil fertility, weed science, soybean varieties and cropping systems, grain sorghum variety trials, plant pathology and entomology.
Through station educational activities such as the annual Wheat Field Day, Sidwell hosted literally thousands of guests over the years, including agricultural producers, commodity groups, foreign dignitaries, national and state legislators and numerous other officials, representatives and individuals from the public and private sectors.
“Dr. Sidwell was an important part of our Wheat Improvement Team, working to ensure wheat growers were able to take advantage of improved crop varieties and research-based best management practices,” Coon said. “He really was one of the great ambassadors of the land-grant mission, helping Oklahomans improve the quality of life for them, their families and their communities.”
The Sidwells – Raymond, his wife Brenda and their children Bambi and Brady – have long been highly regarded members of Oklahoma’s agricultural and agribusiness communities, and are recognized by their farmer peers as very progressive and proactive production agriculturalists.
An OSU agricultural economics alumnus and president of Sidwell Seed and the newly established Enterprise Grain Company located in Kremlin, Brady Sidwell said his father implemented many science-proven practices into the family operation that were backed by cutting-edge research done at the North Central Research Station under his guidance.
“Our family is both extremely proud as well as humbled to have this opportunity to honor our father in such a way,” he said. “Research and Extension programs at land-grant institutions play a critical role in Oklahoma and American agriculture.”
Sidwell added the family is grateful to be able to do their part in further promoting the work being done by the OSU Wheat Improvement Team.
“As a longstanding certified seed wheat producer, we will continue to utilize the best-in-class seed genetics being released by OSU every year and know that the new Dr. Raymond Sidwell Research Facility will only help this already well-respected program reach new heights,” he said.
For Bambi Sidwell, she always knew how passionate her father was about agriculture, in general, and wheat improvement, in particular.
“Growing up on our family farm near Goltry, our dad had an excitement about continuously improving wheat production,” she said. “He enjoyed sharing ideas with other producers that would have a significant and positive impact on people’s lives and their farming operations. Our dad was keen on maintaining a meticulously clean operation, something we strive to continue today.”
An OSU agribusiness alumna, Bambi said the family is proud to be able to take part in honoring her father in a way that enhances research and educational programs conducted at the Lahoma experiment station. Funding for the new facility was made through the Sidwell family, the Sitlington Trust and OAES.
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: I had limited trips outside of Stillwater this past week, and only was able to contact one County Educator before writing this today. Wheat around Stillwater is mostly at various stages of head emergence. I did see a few anthers on scattered heads, but not many. By contrast, Aaron Henson (County Educator; Tillman County in south-central OK) indicated wheat in his area is mostly at flowering.
During this past week, I had several calls about spraying wheat with a fungicide. Although rust (stripe and leaf rust) didn’t appear to increase this past week, conditions reverted to being more favorable for stripe rust development with rainfall, increased dews, and favorable temperature. With more rains and cool temps in the forecast, stripe rust could “reactivate” again, and leaf rust will start to come into the picture. Wheat is now at the point where it will quickly move past the stage (the start of flowering) where it can be sprayed with most fungicides. As far as I know, all wheat foliar fungicides (with the exception of Prosaro) must be applied prior to the start of flowering (Feekes’ growth stage 10.5). Prosaro can be applied through growth stage 10.5.1, which is when flowering is just starting (anthers emerged mostly from the middle of heads). Be sure to read all labels regarding a fungicides use on wheat. There also are varying pre-harvest intervals (PHIs) required for the various fungicides, and often the length of time from heading to harvest can be short in Oklahoma. So, be aware of these PHIs, and spray accordingly.
Active sporulation of stripe rust still can be found around Stillwater and the surrounding area. Stan Fimple (County Educator, Pawnee County just to the northeast of Stillwater) sent me the following photos showing active stripe rust. The photo on the top shows an actively sporulating “stripe” of strip rust (yellowish-orange in color), whereas in the photo on the bottom in the “stripes” you can see dark, blackish specks (teliospores) starting to appear.
Other than this, I have seen scattered leaf rust pustules on lower leaves around Stillwater, and powdery mildew also has become more apparent around Stillwater and at Lahoma as reported by Dr. Brett Carver (OSU Wheat Breeder). However, both of these diseases are at low levels on lower leaves but with coming rain and cool temperatures both (especially leaf rust) could continue to increase on the upper canopy. Around Stillwater, barley yellow dwarf spots continue to be observed but the aphids are now gone or at least in much lower in frequency. If heavy rains come over the next 3 or so days, I would imagine aphid populations will be mostly eliminated.
Finally, I want to raise awareness once again to Fusarium head blight (scab) of wheat. When wheat flowers it is susceptible to infection by the Fusarium fungus that causes scab. That time is quickly approaching. Occasionally Oklahoma has problems with this disease, typically more so in eastern/northeastern Oklahoma than through the central and western parts of the state. However, scab was severe across the state for a couple years around 2010 and there also was some reported last year. For more information on scab, please see PSS-2145 (Fusarium Head Blight (Head Scab) of Wheat: Questions & Answers) and PSS-2136 (Considerations when Rotating Wheat Behind Corn) that can be found at: wheat.okstate.edu. An additional resource is the Fusarium Head Blight Prediction Center at http://www.wheatscab.psu.edu/. At this site you can read commentaries submitted by specialists from each state but more importantly see if weather conditions in your area have been conducive to development of FHB. The site is easy to use and especially may be beneficial in helping make fungicide application decisions.
Reports/excerpts of reports from other states:
Louisiana: Dr. Stephen Harrison, Wheat & Oat Breeder, Louisiana State University, Apr 15, 2016: My research associate (Kelly Arceneaux) is at the Rice Research Station in Crowley (Southwest) Louisiana rating plots today. We plant a double-headrow set of a number of nurseries every year for disease screening at this location in collaboration with Don Growth (rice pathologist). This site is inoculated with scabby corn but is not misted due to the abundance of humidity and free moisture at this site. Nurseries include: Statewide Variety Trial, Uniform Southern Soft Red Winter Wheat Nursery, Uniform Southern Scab Nursery, Sunwheat, GAWN. Kelly reports that stem rust is heavy and widespread at this site. Leaf rust is moderate and scab is at an intermediate level, which is good for distinguishing lines. The earliest plots are starting to mature, probably just past soft dough, while the latest lines are just past heading or not vernalized and not going to head. We only received about 50% of our normal vernalization hours this winter and quite a few lines in the statewide variety trials will not be harvested due to vernalization issues.
Nebraska: Dr. Stephen Wegulo, Extn Plant Pathologist, University of Nebraska, April 14, 2016: “On Friday April 8, Jenny Rees, UNL Extension Educator, found trace amounts of stripe rust in a wheat field in Nuckolls County in south central Nebraska. Earlier this week, samples from several wheat fields in Banner County submitted to the lab of Dr. Bob Harveson (Extension Plant Pathologist) at UNL’s Panhandle Research and Extension Center in Scottsbluff were positive for stripe rust and leaf rust. This week on April 12 and 13 I surveyed wheat fields in the southernmost tier of counties in southeast, south central, and west central Nebraska. Dry weather which has prevailed over the last two weeks or so stopped rust development. I did not find rust in any of the fields I visited in the southernmost tier of counties. Several fields showed symptoms of stress from lack of moisture. Today I looked at research plots at Havelock Farm here in Lincoln (Lancaster County) and at the Agricultural Research and Development Center (ARDC) near Mead (Saunders County, about 35 miles north of Lincoln). I found a few hot spots of stripe rust at Mead (see first attachment), mostly on the lower leaves. I also found trace levels of leaf rust at Mead (second attachment). Powdery mildew was the predominant disease at Lincoln and Mead, but I also saw significant levels of Septoria tritici blotch in one research field at Mead. Wheat growth stage across the state ranges from Feekes 5 and 6 (most fields) to Feekes 7 in some irrigated fields.”
South Dakota: Dr. Emmanuel Byamukama, Extension Plant Pathologist, South Dakota State University; Apr 13, 2016: “Several winter wheat fields in central South Dakota were scouted yesterday for stripe rust. One field originally found with stripe rust last week was the only one we found with stripe rust. Stripe rust was found on old/dying leaves and some of the leaves had teliospores, indicating the source of this rust would have been from overwintered stripe rust in South Dakota.”
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Wheat has advance in maturity across OK this past week flag leaves definitely are emerging around Stillwater. From reports I’ve received I believe across the state wheat ranges from flag leaves emerging to heads starting to emerge (although wheat in far northwest OK and the panhandle may not be quite as far along). I didn’t hear specifics but was told that freeze damage has been observed around Kingfisher in central OK. With frost/freezing temps again last night, additional damage is possible. Drought, although not as bad as last year, also is creeping back into the picture. One producer from southwestern OK indicated to me that “leaves are rolling-up at 2 o’clock in the afternoon.” I didn’t see any wheat that looked stressed, but in several locations had to dig 4” or more to find moist soil.
In my trips this past week to central OK (Watonga) and to more north-central OK (Blackwell), I could find stripe rust, but it doesn’t appear to me that it had advanced (become more severe). In fact, Zack Meyer (Extn Educator; Kingfisher Cnty) sent me the following photo that shows the telial spore stage of the stripe rust fungus forming on wheat leaves. Look closely at the photo and you can see minute yellowish-orange pustules of stripe rust also present on the leaves (especially the greener leaf). The telial stage is considered more of a survival spore stage and indicates that stripe rust is encountering unfavorable conditions and starting to shut down. Although this is good news, stripe rust can quickly “reactivate” if favorable temperature and moisture are resumed.
Unfortunately there also is a lot of active stripe rust still in the state as I have had numerous calls from across OK to discuss spraying options, and Greg Highfill (Extn Educator; Woods Cnty) sent me the following photo showing moderate/severe and active stripe rust on wheat in northern-central OK.
Reports/excerpts of reports from other states: No reports from Texas, but did hear the following from Kansas and Nebraska.
Kansas: Dr. Erick DeWolf; Extn Plant Pathologist; Kansas State University; Manhattan, KS; Apr 1, 2016: “The Kansas wheat crop is progressing rapidly through the jointing stages of development in much of the state. Wheat in the Southeast portion of the state is at or fast approaching flag leaf emergence. The crop is generally considered to be two or three weeks ahead of schedule.
Scouting reports indicate that stripe rust is becoming established in the 2016 wheat crop. This past week, stripe rust was reported in many counties in central and eastern Kansas. The disease is still at low levels in most fields with a few exceptions in Southeast Kansas. This early establishment of stripe rust increases the risk of severe yield loss and growers should continue to monitor the situation carefully. If weather conditions become favorable, the disease could spread rapidly from the lower leaves, where it is now established, to the upper leaves that are critical for grain development. Leaf rust is still active in the western tier of counties bordering CO but remains a low levels in most fields. Powdery mildew is severe in some fields in central and eastern Kansas.”
Nebraska: Dr. Stephen Wegulo; Professor/Extn Plant Pathologist; University of Nebraska-Lincoln; Lincoln, NE, KS; Mar 31, 2016: “Yesterday March 30, 2016: Jennifer Rees, UNL Extension Educator, found trace levels of actively sporulating leaf rust in wheat fields in Nuckolls County in south central Nebraska. Nuckolls County is in the southernmost tier of counties that border Kansas. She did not find actively sporulating stripe rust; however, in one field there was evidence of stripe rust that was active last fall.”
Colorado: Dr. Kirk Broders; Ast Professor; Colorado State University; Ft. Collins, CO; Mar 29, 2016: “As I mentioned last week stripe rust is now present in eastern Colorado with a confirmed report of stripe rust in the Prospect Valley region northeast of Denver. We have received several reports of stripe rust from that same region. This past week was windy with some precipitation in this area of Colorado, so spores were spread but there was limited moisture to promote additional infection. There is rain in the forecast for this coming week and the rain is certainly needed for the wheat, but also will provide a favorable environment for stripe rust to increase because temperature is supposed to be staying in the 50s-70s for the days and 20s-40s at night. If you already have noticeable levels of rust in your field you may want to consider including a fungicide at tillering (GS 4) or when you make your herbicide application. If you do not currently have rust in your fields or in your region, I would recommend waiting until closer to flag leaf and monitor the spread of stripe rust in the state. CSU Extension specialist Wilma Trujillo was able to examine wheat in the southwest part of the state near Lamar, where stripe was present last fall. We examined these leaves and found no evidence stripe rust was able to overwinter in this region of the state. It is still early in the season, but there is certainly the possibility for stripe rust to become a serious problem in the state again this year. There are also the threat of leaf rust we should not forget about. Leaf rust has been present in western Kansas for the last 2 weeks and has likely moved into eastern parts of the state. I have not received in specific reports, but would appreciate you feedback if you have observed either stripe rust of leaf rust in you fields.
By Tom Royer, OSU Extension Entomologist
I have received several reports of (and photos, Figure 1) of bird cherry oat aphid (BCOA) numbers in winter wheat that will require treatment with an insecticide
Bird cherry oat aphids are small (2mm) olive-green aphids with a red-orange patch surrounding the base of each cornicle (Figure 1). Old, wingless, overwintering adult aphids are darker, almost black. At this time, you may also find winged aphids that have moved in to the field (Figure 2).
What are my suggestions regarding control of bird cherry oat aphid in winter wheat?
- Unpublished research provided by Dr. Kris Giles (OSU) and Dr. Norm Elliott (USDA-ARS) along with studies conducted in South Dakota, Minnesota, and North Dakota on spring wheat indicated that BCOA causes yield loss before wheat reaches the boot stage. Approximately 5-9% yield loss occurs when there are 20-40 BCOA per tiller (average 7%).
- Visible damage from bird cherry-oat aphid is not very noticeable so infestations may go unnoticed. It is very important to check fields for infestations and make treatment decisions only after a field has been checked.
My suggestion for making a treatment decision is as follows:
If greenbugs and bird cherry oat aphids are both present, use Glance n’ Go to scout, which can be accessed at http://entoplp.okstate.edu/gbweb/index3.htm. Published research from Giles and Elliott showed that Glance n’ Go sampling will work with both aphids if they are both present.
If bird cherry-oat aphid is present alone, count the number of aphids present on each of 25 randomly-selected tillers across a zigzag transect of the field. The reason that you can’t use Glance n’ Go is that the most available research suggests that the threshold is too high to effectively use Glance n’ Go.
Look for evidence of parasite activity in the form of mummies (Figure 3). A rule of thumb is that if 5-10% of the aphids are mummies, more than 90% are already parasitized. If mummies are not present, use the guidelines below to make a treatment decision.
If, after thoroughly scouting your field, you can identify that infestations are spotty, consider spot spraying with a ground rig.
Use the YIELD LOSS TABLE to determine a potential YIELD LOSS from the aphids. Then estimate your CROP VALUE and calculate your CONTROL COSTS. Use those numbers to estimate PREVENTABLE LOSS. If estimated PREVENTABLE LOSS is greater than CONTROL COSTS, Treat; otherwise, Don’t Treat.
Here is an Example:
Step 1: Estimate YIELD LOSS:
- Total # aphids_______525___________/25 tillers = average # aphids/tiller_____21_____
Step 2: Estimate CROP VALUE: (Crop Value = Yield potential X Price per bushel)
- Yield potential__40____ bushels/acre X price per bushel $____4.50____ per bushel
CROP VALUE = $___180____
Step 3: Estimate CONTROL COSTS: (Control Cost = Insecticide Cost + Application Cost)
- Insecticide cost $___6_____ /acre + Application Cost $ ____3_____/acre
CONTROL COSTS $_____9_____/acre
Step 4: Estimate PREVENTABLE LOSS (Crop Value X Yield Loss from Aphid)
- Crop value/acre $___180_____ x Yield Loss from aphid ___0.07_____
PREVENTABLE LOSS $____12.60______/acre
IF PREVENTABLE LOSS $___12.60_____ is greater than CONTROL COSTS $___9.00_____ TREAT
IF PREVENTABLE LOSS $________ is less than CONTROL COSTS $__________ DON’T TREAT
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 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 updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: This past week I looked at wheat around Stillwater as well as in central OK (Blaine County NW of Oklahoma City; Kingfisher just NW of OKC; Apache in Caddo County SW of OKC), and in SW OK around Altus. I saw wheat as far along as approaching flag leaf emergence to at growth stage 6-7. The more advanced wheat typically was planted relatively early and not grazed. Everywhere I was had sufficient moisture, although areas in southwestern and western OK were getting to a point where some rain definitely would be beneficial. In addition to my observations, I’ve received numerous reports that I’ll summarize here.
At nearly all the places I stopped, I observed varying levels of stripe rust, leaf rust, aphids, and powdery mildew, with powdery mildew being by far the least prevalent. Stripe rust typically was scattered across fields, but there were some significant hot spots. In some fields (for example the variety trial at Kingfisher) I saw no stripe rust. Greg Highfill (Extn Educator, Woods County) and Darrell McBee (Extn Educator, Harper County) sent me the photo below showing stripe rust they found this past week. They indicated the stripe rust was scattered and not common, but this does mean that spores are present in the field and will increase with favorable (cool and wet) weather. They also indicated finding a little powdery mildew. I also heard reports of severe stripe rust in susceptible varieties such as Pete, Garrison, and Everest.
More severe hot spots of stripe rust were reported by David Nowlin (Extn Educator; Caddo County), who sent the following photo of stripe rust on ‘Pete’, which is highly susceptible to stripe rust.
Similar reports regarding stripe rust were made by Dr. Brett Carver. He also has reported seeing considerable chlorosis (yellowing) often with the lack of sporulation. I saw the same type of yellowing with no sporulation at Kingfisher yesterday (see photo below). I’m not sure of the cause of this yellowing, but I don’t believe it to be from rust or other foliar diseases because it is widespread in its distribution on lower leaves. Perhaps it is the result of the environment.
In no-till fields near Altus and Apache I saw striking tan spot on lower leaves along with numerous pseudothecia of the tan spot fungus on the wheat residue in the field. Near Altus, this was combined with stripe rust presence such as described above. In such a case, applying a fungicide early to catch both of these diseases should be considered, especially if the field at this point has a good yield potential. For more information to help make this decision, see OSU CR 7668 available at www.wheat.okstate.edu
Reports/excerpts of reports from other states:
Texas : I’ve only received two reports from Texas this past week. One is from a former student that now lives in the Weatherford, TX area. He indicates that stripe rust is in the area. The other report is from David Nowlin (Extn Educator, Caddo County), who indicates a colleague of his located near Denton, TX sent him the following report on 15-March.
“We’re getting hammered with strip and leaf rust as well as powdery mildew on our varieties down here in Denton, TX. We’re just a little further ahead of you. Wheat is not as far along as we normally see.
Kansas: Dr. Erick DeWolf; Extn Plant Pathologist; Kansas State University; Manhattan, KS; Mar 19, 2016: “The wheat crop is growing rapidly throughout Kansas. The crop in the more advanced fields are approaching jointing in the northwest and are about a week away from flag leaf emergence in the south central and southeast portions of the state. The crop is generally considered to be about 3 weeks ahead of schedule with respect to normal growth and development. There are multiple reports of leaf rust and stripe rust in Texas, Oklahoma, and other surrounding states.
The Crops Extension team has been busy scouting for disease in recent weeks. We are finding active leaf rust and stripe rust in the state. Leaf rust was reported in west central and northwest, Kansas with most activity in counties bordering Colorado. Low levels of leaf rust were also observed in research plots in Riley County, which is located in northeast Kansas. The winter has been very mild in Kansas and it is very likely that the leaf rust has overwintered in the state. Stripe rust was reported in multiple counties this past week. Stripe rust is generally at very low levels with most activity reported in the southeast portion of the state. Tan spot and powdery mildew have also been reported in some areas of the state.”