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David Marburger

David Marburger

Since April 2016, I have served as the Small Grains Extension Specialist at Oklahoma State University. My research and extension efforts focus on delivering science-based recommendations in order to increase small grains production and profitability for stakeholders throughout Oklahoma and the southern Great Plains.

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Hessian fly showing up in SW OK

Gary Strickland, Jackson and Greer Co. Ag Extension Educator, has indicated a number of wheat fields in that area of SW OK are showing signs of Hessian fly. Most of these fields are no-till and planted with a susceptible wheat variety such as Fuller. Plant symptoms may go unnoticed until you start to see tillers dying, a good indication of an infestation. Further investigation by removing the plant and examining the stems at the base near the crown will help identify any larvae or pupae present. Dr. Tom Royer, Extension entomologist, recently wrote a nice article depicting how and what to look for: Plan to Manage Hessian Fly.

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Full-grown Hessian fly larvae form rice-like puparia that are shiny and dark brown. The puparium is commonly referred to as a “flaxseed.” Photo courtesy of Dr. Jeff Edwards.

Now would be a good time to scout your fields for this pest, especially if you have fields which are planted with a non-treated susceptible wheat variety, are in a continuous wheat rotation, use no-till or minimum tillage, were planted early (September into early October), or is a conventional tilled field next or near to a no-till wheat field. If you are unsure whether your wheat variety is resistant to Hessian fly, you can use this OSU fact sheet: Wheat Variety Comparison ChartUnfortunately, not much can be done to control this insect right now. However, we can learn from this year and make some management adjustments to control this pest next year.

For more information on Hessian fly and its management, consult fact sheet EPP-7086, Hessian Fly Management in Oklahoma Winter Wheat.

Wheat Disease Update – 30-November-2016

This post was written by Dr. Bob Hunger

Extension Wheat Pathologist

Department of Entomology & Plant Pathology

Oklahoma State University

During the first week of November 2016, I reported observing fairly severe leaf rust in rows of Jagalene wheat in Dr. Brett Carver’s breeder nurseries here at Stillwater.  About that time, leaf rust also was observed in the early planted variety-demonstration nursery planted in Stillwater by Dr. David Marburger.  The early planted plots were planted 13-Sep-2016.  For this variety-demonstration, Dr. Marburger plants a duplicate, later planted (26-Oct-2016) plot of each variety immediately in front of the early-planted plot.  This variety-demonstration nursery has provided an interesting observation of the effect of planting date on leaf rust as can be seen in Figure 1.

With cooler temperatures and light frosts we finally have received over the last 7-10 days, the older leaves infected with leaf rust in the early planted plots have mostly turned yellow.  Rust pustules are evident, but chlorosis (yellowing) is the predominate symptom.  Across all the varieties (>60), there is a range from nearly all yellow except the youngest leaves, to nearly all green (there is some tip yellowing/burning from the frosts).

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By comparison, look at the photo below (Figure 2) showing early planted plots (background) and late planted plots in the foreground.  Leaf rust is not found in the late planted plots (foreground).  If early planted wheat had been grazed, which would be more typical with a mid-September planting date, much of the rank foliage would have been removed and rust would not be nearly as severe as in this variety-demonstration.  This is a good example of how planting date can effect disease incidence and severity given an environment favorable for disease such as we have had this fall with mild temperature and occasional rain and dews.

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There are a couple of additional points I should make with the photos above.  First, not many would plant wheat in early to mid-September for the purpose of grain only.  Hence, wheat in the early planted plots would most likely be grazed, which would remove much of the rank foliage and also the rust, and thereby the rust incidence would not be nearly as severe.  Wheat in a grain-only mode would look more like the wheat in the late planted plots (foreground plots in Figure 2).  Second, we normally would have colder weather earlier than we had this year that would have arrested rust development.  Then, newly emerging leaves would be healthy and green.  As I have said previously, I am not a proponent of spraying in the fall to control fall foliar diseases such as leaf rust because leaf rust development typically slows and stops once we get to colder temperatures in November-January (basically <60 F with frosts at night).  And remember, the primary concern with fall leaf rust is that with a mild winter and sufficient moisture, the rust will survive through the winter and inoculum will be present in fields to start the disease early in the spring.  Hence, monitoring of fields through the late winter and early next spring is recommended to see if application of a fungicide to control rust is indicated in the early spring.  For all the foliar wheat diseases (leaf rust, stripe rust, powdery mildew, tan spot, and septoria leaf blotch), control in the spring is more critical then control in the fall.  I have heard of fungicide being added in with a fall herbicide application to limit disease, but such an application would have needed to have been applied 3-4 weeks ago to prevent the situation as depicted in the photos above.  However, I can see where in a year such as this one with a fully susceptible variety that was planted early and not grazed there may be value to an early fungicide application.  BUT ESPECIALLY, watch these fields starting in late February to see if an application is merited because control of foliar diseases in the spring is much more critical than control in the fall.

Wheat Disease Update – 08-November-2016

This post is written by Dr. Bob Hunger

Extension Wheat Pathologist

Department of Entomology & Plant Pathology

Oklahoma State University

Fall 2016 has been mild/warm and relatively dry. Because of the dryness, fall foliar diseases should be relatively sparse, but some areas have received sufficient rain or had sufficient dews to favor development of wheat foliar diseases. That is the case around Stillwater as you can see in the photo below. This picture, which was taken November 5th in one of Dr. Brett Carver’s wheat breeding nurseries at Stillwater, was planted September 14th. The variety is Jagalene, which is highly susceptible to both leaf and stripe rust (I could find no stripe rust).

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Wheat foliage (‘Jagalene’) showing a highly susceptible reaction to leaf rust with an intermediate severity level. Note younger leaves show no leaf rust. This nursery is located in Stillwater, OK, and was planted 9-14-2016 with this photo taken on 11-5-2016.

 

I am not a proponent of spraying in the fall to control fall foliar diseases such as leaf rust because leaf rust development slows and stops once we get to winter temperatures in late November-January (basically <60 F). Typically the lower/older leaves with leaf rust pustules die, but the youngest leaves are green and healthy. Grazing helps to remove leaf rust infections, is not harmful to cattle, and also “opens” the canopy so there is increased air circulation and drying that are less favorable to development of leaf rust. Given these considerations, spraying to control leaf rust in the fall typically is not necessary.  The primary concern with fall leaf rust is that with a mild winter and sufficient moisture, the rust will survive through the winter and inoculum will be present in fields to start the disease early in the spring.  Hence, monitoring of fields through the late winter and early next spring is recommended to see if application of a fungicide to control rust is indicated in the early spring.

 

Other samples that have come to the lab for diagnosis appear to be related to abiotic conditions such as dryness or low fertility.  Some leaf spots have been observed on these samples, but they are either secondary or of low incidence and not a cause of major concern. Dr. Misha Manuchehri (OSU Weed Specialist) sent the following photo showing leaf spots she observed on plants in a trial located near Perkins, OK. Dr. Manuchehri is bringing a sample for us to isolate from, but this appears to be tan spot. Leaf spotting diseases such as tan spot and Septoria leaf blotch typically do not appear until late February or March.

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Leaf spots (most likely tan spot) on wheat foliage (variety not known). This nursery is located near Perkins, OK. Photo taken the first week of November 2016 by Dr. Misha Manuchehri.

 

For all the foliar wheat diseases (leaf rust, stripe rust, powdery mildew, tan spot, and Septoria leaf blotch), control in the spring is more critical then control in the fall. I have heard of growers adding a shot of fungicide with a fall herbicide application to limit disease present. I have no data to support the value of such an application, but there may be some value to it because plants are smaller and not growing as actively so limiting the amount of foliage loss due to a disease such as tan spot will contribute to the overall health of the wheat going into winter.  BUT ESPECIALLY, watch these fields starting in late February to see if an application is merited because control of foliar diseases is much more critical in the spring than in the fall.

**ATTENTION** New date for the herbicide symptomology clinic!

We will be having the 2nd Annual Herbicide Symptomology Clinic at the Agronomy Research Farm in Stillwater on Friday, November 4.  The flyer below includes all details, but topics covered will include herbicide demonstrations for wheat and canola as well as many winter weeds, simulated drift demonstration, and discussion on sprayer nozzle selection for specific tasks.  Please plan on attending if possible, and contact Dr. Manuchehri for an RSVP.  Thank you!

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Mark your calendars for November 2nd!

We will be having the 2nd Annual Herbicide Symptomology Clinic at the Agronomy Research Farm in Stillwater.  The flyer below includes all details, but topics covered will include herbicide demonstrations for wheat and canola as well as many winter weeds, simulated drift demonstration, and discussion on sprayer nozzle selection for specific tasks.  Please plan on attending if possible, and contact Dr. Manuchehri for an RSVP.  Thank you!

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Scout for fall armyworm!

With wheat planting beginning in some areas of the state during the last week of August into the first week of September, we have already received several calls regarding fall armyworm feeding. Dr. Tom Royer, Extension entomologist, said fall armyworms have been very active this summer, showing up early and in large numbers this growing season.

As wheat planting progresses here in September, producers need to check fields very regularly after seedling emergence. One producer had significant damage occur across an entire 1/2 section within 2 days. Dr. Royer suggests scouting for fall armyworms by examining plants in several (5 or more) locations in the field. A good place to start is along the field margin as they sometimes move in from the road ditches and weedy areas, but make sure to examine the interior of the field as well. Fall armyworms are most active in the morning or late afternoon.

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Fall armyworms are small (3/8-1 1/2″) and can be easily overlooked (top photo). Feeding on leaves gives a transparent (“window paned”) appearance (bottom photo). Photos courtesy of Dr. Tom Royer.

Be on the lookout for “window paned” leaves, and count all sizes of larvae. The suggested treatment threshold is 2-3 larvae per linear foot of row in wheat with active feeding. Numerous insecticides are registered for control, but they are much more susceptible when caterpillars are small. We won’t get relief from fall armyworms until we get a killing frost. So make sure to keep scouting regularly, especially with early-planted wheat!

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Fall armyworm can cause significant damage across large areas very quickly, so scout early and scout often. Photo courtesy of B. Boeckman.

Control suggestions for fall armyworm are available in the OSU Fact Sheets CR-7194 Management of Insect and Mite Pests of Small Grains.

Wheat Disease Update – 04-Aug-2016

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 dateMuch 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:

http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-7836/CR-7088web2012.pdf

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.

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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.

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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)

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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:

http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-6189/EPP-7086web2015.pdf

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).

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Seed treatmentsThere 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.

2015-2016 Wheat Crop Overview

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
2015 2016
Harvested Acres 3.7 million 3.3 million
Yield (bu/ac) 26 40
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.

Wheat Disease Update – 08 June 2016

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) – bob.hunger@okstate.edu
 
I thought last week was my final update, but over the last week I have received a couple reports of “dark” wheat appearing in wheat fields in Oklahoma such as the one below from near Cordell, OK (Washita County).  This condition, which is known as sooty mold, results from various fungal molds growing on the dead plant matter in the wheat heads.  Sooty mold typically appears when wheat that is turned cannot be cut in a timely manner.  It also seems to be more prevalent where wheat received less than optimum fertility, freeze occurred, or something else resulted in less vibrant plants.  Wet weather, high humidity, and late harvest then provide an ideal climate for secondary fungi to colonize the dead tissue causing the sooty appearance to the wheat.  Typically the sooty mold occurs in areas of a field where moisture and/or humidity is highest.  Test weight and yield can both be affected, but often the biggest problem with sooty mold is that it will result in black point of wheat kernels (photo below).  With time, sooty mold fungi colonize (typically) the germ end of the wheat kernel giving the kernel a black point.  Often such wheat grain has reduced viability, and use of heavily black-pointed wheat as seed wheat should be avoided.  Typically there are no actions to take to prevent sooty mold/black point other than to try to harvest wheat as quickly as possible once the wheat has turned.
 
Sooty mold in wheat field – Andy Evans         Wheat head with sooty mold
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Black point of wheat kernels (bottom row of wheat kernels)
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Wheat Disease Update – 28 May 2016

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) – bob.hunger@okstate.edu

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.”

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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.”

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Severe stripe rust in South Dakota – Dr. Emmanuel Byamukama