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Disease and insect issues to consider prior to planting

Planting date:  Much of the winter wheat in Oklahoma is sown with the intent of being used as a dual-purpose crop. In this system wheat is grazed by cattle from late October to early March, 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)

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.  Wheat infected in the fall is either killed by the next spring or will be severely damaged.  Seed treatments are not effective in controlling these 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 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)

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.

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.  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)

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).  Controlling root and foot rots is difficult.  There are no resistant varieties, and although fungicide seed treatments with activity toward the root and foot rots are available, their activity usually involves early-season control or suppression rather than control at a consistently high level throughout the season.  Often, there also are different “levels” of activity related to different treatment rates, so again, CAREFULLY read the label of any seed treatment to be sure activity against the diseases and/or insects of concern are indicated, and be certain that the seed treatment(s) is being used at the rate indicated on the label for activity against those diseases and/or insects.  Later planting (after October 1 in northern Oklahoma and after October 15 in southern Oklahoma) also can help reduce the incidence and severity of root rots, but planting later will not entirely eliminate the presence or effects of root rots.  If you have a field with a history of severe root rot, consider planting that field as late as possible or plan to use it in a “graze-out” fashion if that is consistent with your overall plan.  For some root rots, there are specific factors that contribute to disease incidence and severity.  For example, a high soil pH (>6.5) greatly favors disease development of the root rot called take-all.  OSU soil test recommendations factor in this phenomenon by reducing lime recommendations when continuous wheat is the intended crop. Another practice that can help limit take-all and some of the other root rots is the elimination of residue.  However, elimination of residue by tillage or burning does not seem to affect the incidence or severity of eyespot (strawbreaker).

Seed treatments:  There are several excellent reasons to plant seed wheat treated with an insecticide/fungicide seed treatment.  These include:

  1. Control of bunts and smuts, including common bunt (also called stinking smut), loose smut, and flag smut (for more information on flag smut, go to end of this report).  The similarity of these names can be confusing.  All affect the grain of wheat, but whereas common bunt and flag smut spores carryover onseed or in the soil, loose smut carries over in the seed.  Seed treatments are highly effective in controlling all three of these 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 “2015 OSU Extension Agents’ Handbook of Insect, Plant Disease, and Weed Control (OCES publication E-832),” and/or contact your County Extension Educator.
  2. Enhance seedling emergence, stand establishment and forage production by suppressing root, crown and foot rots.  This was discussed above under “Root and Foot Rots.”
  3. Early season control of the aphid/BYDV complex.  This can be achieved by using a seed treatment containing an insecticide.  Be sure that the treatment includes an insecticide labeled for control of aphids.
  4. Control fall foliar diseases including leaf rust and powdery mildew.  Seed treatments are effective in controlling foliar diseases (especially leaf rust and powdery mildew) in the fall, which may reduce the inoculum level of these diseases in the spring.  However, this control should be viewed as an added benefit and not necessarily as a sole reason to use a seed treatment.
  5. Suppression of early emerged Hessian fly.  Research suggests that some suppression can be achieved, but an insecticide seed treatment has little residual activity past the seedling stage.

A final consideration for fall 2015:  In the text above, I made reference to “flag smut,” which is a smut of wheat I have not mentioned previously.  Flag smut occurs in the U.S., in particular, the Pacific Northwest.  It also has been reported in the Plains States, being first reported in Kansas in the 1920s.  However, flag smut has not been observed in the Central Plains for many years until this past spring when it was found in around 20 counties in Kansas from April-June.  No flag smut was observed on wheat in Oklahoma in 2015, but much of the wheat in Oklahoma had been harvested when I found out about flag smut occurring in Kansas.  Flag smut is similar to common bunt (stinking smut) in terms of its disease cycle, but spores of this fungus erupt through the leaves rather than replace the wheat grain as with common bunt.  Additionally, leaves and tillers infected with flag smut often are twisted and deformed.

For more information on flag smut, please go to the following links.  The first link is to a press release made in mid-July, 2015 on the finding of flag smut in Kansas.  The second link is a KSU fact sheet on flag smut.

http://www.ksre.ksu.edu/news/story/wheat_smut071515.aspx

http://www.bookstore.ksre.ksu.edu/pubs/MF3235.pdf

By: Dr. Bob Hunger, Extension OSU Wheat Pathologist and Dr. Tom Royer, OSU Extension Entomologist

Wheat streak mosaic virus showing up

Add wheat streak mosaic virus to the list of possible causes of yellowing wheat in Oklahoma. Wheat streak mosaic virus is transmitted by the wheat curl mite, which oversummers on grasses such as volunteer wheat and corn. The wheat curl mite cannot survive more than two weeks without a green host, hence the recommendation to make sure that all grass plants are dead two weeks prior to planting. You can find more information on the wheat curl mite and wheat streak mosaic in OSU Fact Sheet EPP-7328 – Three virus disease of wheat in Oklahoma

The photo below is from our wheat variety trial at Kildare. As you can see there is significant yellowing in some of the plots. Our first thoughts were that either wheat soilborne mosaic virus and/or wheat spindle streak mosaic virus were causing the symptoms; however, the yellowing was present in many varieties that are resistant to both these diseases. The Disease Doctor, Bob Hunger, collected samples for analysis in the OSU Plant Diagnostic Lab. Tests showed that wheat streak mosaic was the culprit.

Wheat streak mosaic virus is responsible for yellowing at our Kildare variety trial. All varieties are affected by the disease, but as shown in this picture the severity of the reaction differs somewhat by variety.

Wheat streak mosaic virus is responsible for yellowing at our Kildare variety trial. All varieties are affected by the disease, but as shown in this picture the severity of the reaction differs somewhat by variety.

We are facing this problem because I did not follow my own recommendations. While the plot area was mostly clean at the time of planting, there was some volunteer wheat present. We planted anyway and sprayed glyphosate right after planting. In the past wheat streak mosaic virus was primarily a northwestern Oklahoma issue and we could get by with late burndown on wheat ground in central Oklahoma. Our Kildare plots are a prime example that this is no longer the case. We have to control volunteer grasses (wheat, corn, grain sorghum, etc.) in a manner that will break the green bridge for at least two weeks prior to planting.

So, what is next for our plots at Kildare? There are some variety differences in reaction to the wheat streak mosaic virus. We will rate plots and include this information in our wheat variety comparison chart. I anticipate the plots will continue to go downhill and it is yet to be determined whether or not we will be able to harvest useable data from the location. We will certainly try again next year and apply our turndown earlier.

 

Wheat disease update 05 June 2013

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist

Oklahoma:

Not a lot to add since the last report and this is likely the last one from Oklahoma unless something out of the ordinary occurs.  Wheat is being harvested in southwestern OK.  I’ve heard reports that ranged from “about 180 bu from 50 some acres” up to around 30 bu/acre.  Wheat around Stillwater is typically at medium dough with very little green leaf tissue left in the leaves.  Stems are still mostly green but also beginning to fade.  All of the wheat I looked at on Monday had 3 plump kernels/mesh.

A field day last Thursday (30-May) in Pawnee County (30 miles northwest of Stillwater) revealed a trial and surrounding field with severe leaf spot.  Isolations from 3 varieties all yielded Pyrenophora (tan spot) and Septoria/Stagonospora with tan spo (Pyrenophora) more common than the other two.  The wheat was approaching dough, so I don’t think there will be a huge yield hit – especially given the moisture and cool spell we have been having.  I have only rarely seen tan spot and the leaf spot diseases in general this severe in Oklahoma.

Dr. Ned Tisserat (wheat Pathologist at Colorado State University) confirmed our suspected diagnosis of bacterial streak/black chaff in the variety trial at Chickasha (about 40 miles southwest of Oklahoma City).  Symptoms were widespread and quite severe across all varieties, but similar symptoms due to leaf spots, drought, and freeze also contributed to the overall burnt appearance to the trial.

Finally, Bryan Vincent (crop consultant – north central OK) sent in photos of isolated spots in a wheat field in Kay County (just south of Kansas in north central OK).  Although no sample was submitted, the photos and description of the situation definitely indicated this to be take all.

Reports/excerpts of reports from other states:

KansasDr. Erick De Wolf (Professor/Small Grains Extension Pathologist, Kansas State Univ, Manhattan, KS) 03-Jun-2013: Fields in Central Kansas are maturing rapidly now and many fields were at the milk stages of development last week.  The levels of stripe rust and leaf rust remain low in Kansas this year despite some earlier reports of stripe rust when the wheat was heading.  It appears higher temps have slowed the development of stripe rust.  Only trace levels of stripe rust can be found in most plots and commercial fields I visited May 27-31in Republic, Smith and Phillips counties (North central).  Rust was absent from plots and fields I checked in Eills, Rush, Ness, and Lane counties (west central KS) this year and drought remains a serious issue for these growers.

I observed low to moderate levels of leaf rust in a variety testing location in Reno county (south central KS) on May 31.  The incidence was near 80% but severity was still very low (generally less than 2%) of the flag leaves of susceptible varieties such as Overley, Jagger and Jagalene.  The wheat in this plot was at the milk stages of kernel development so I do not expect any significant yield loss at this location.

 

NebraskaDr. Stephen Wegulo (Small Grains Extension Pathologist, Univ of Nebraska, Lincoln, NE) 30-May-2013:  This afternoon I looked at breeding nursery plots in Lincoln (Lancaster County, southeast Nebraska).  I found trace levels of stripe rust.  The predominant disease was powdery mildew in the lower canopy, followed by leaf spots, mainly Septoria.  There was a low incidence of Fusarium head blight (FHB) at low severity (one spikelet bleached on wheat, more on barley and in one case an entire barley head bleached).  I suspect FHB is going to be a problem in the eastern part of the state.  The timing of heavy, continuous rainfall coinciding with heading and flowering couldn’t be better for FHB development in the eastern part of the state.  We have had these conditions over the last week or so and even before.  Dr. P. Stephen Baenziger, UNL small grains breeder, happened to be at the nursery when I arrived.  He told me his team saw stripe rust at higher than trace levels in a breeding nursery at Mead (about 30 miles north of Lincoln).  Conditions are perfect for rapid development and/or spread of just any fungal or bacterial disease in eastern Nebraska.  I also saw low levels of barley yellow dwarf virus in lines that appeared to be susceptible.  A sample with virus symptoms I brought back from Saline County (also in southeast Nebraska) last week has tested positive for wheat streak mosaic.

Wheat disease update 25 May 2013

Wheat disease updates are written by Dr. Bob Hunger, Extension Plant Pathologist

I and Nathalia Grachet (OSU Graduate Student) returned Friday from a trip and field days in the panhandle of Oklahoma.  Wheat at Lahoma (25 miles west of Enid) ranged from full berry (watery) to the milk stage.  Driving further to the northwest after about Alva was depressing as the condition of the wheat and the landscape in general deteriorated with what seemed like each passing mile.  The field days we attended were at Balko (40 miles east of Guymon) and Hooker (20 miles northeast of Guymon).  Wheat in these trials ranged from flowering to full berry (watery).  Rick Kochenower (Panhandle Area Specialist – Agronomy) related the story that demonstrates the resilience of wheat.  The Balko area was hit hard by the last freeze in April such that he felt there would be no wheat there.  However, a mild May with just a little moisture allowed secondary tillers to come back, and if some rainfall and mild temperatures occurs for the next couple of weeks, some wheat will be harvested in the area.  This is not the scenario over the entire panhandle.  According to Rick, wheat in Cimarron County (far western county in the panhandle) is all but gone primarily due to drought whereas in Texas and Beaver County freeze and drought have both played a role in severely impacting wheat production.

Leaf and stripe rust were found this past week around Stillwater but not at a typical incidence or severity; leaf rust is especially lacking.  Dr. Art Klatt reported being able to easily find leaf rust in his plots near Perkins, OK (15 miles south of Stillwater) in the range of 5-20S, which is lighter than typical.  At Lahoma, Nathalia and I found both leaf and stripe rust but at low incidence and severity (especially leaf rust).  Leaf spotting was more common, but it was difficult to determine if this was Septoria, Stagonospora, tan spot and/or physiological.

Signs of wheat streak mosaic and barley yellow dwarf can still be observed, especially around Lahoma where flag leaves are still mostly green.  In the panhandle and northwestern OK it is difficult to discern virus damage from freeze and drought.

 

Reports/excerpts of reports from other states:

Nebraska – Dr. Stephen Wegulo (Small Grains Extension Pathologist, Univ of Nebraska, Lincoln, NE) 24-May-2013:  Wheat in Nebraska is mostly in the boot to heading growth stages.  There have been no new reports or observations of rust diseases since the observation of stripe rust at Mead on May 7.  On May 21 and 22, I surveyed wheat fields in Lancaster, Saline, and Saunders Counties in southeast Nebraska.  I did not find any rust diseases.  The stripe rust that was observed at Mead on May 7 stopped activity following the high temperatures we had during the week of May 13 (including 100+ deg F on May 14), and never spread, similar to Carl Bradley’s observation in Champaign County, IL.

 

Bacterial streak found in Oklahoma

Widespread leaf spotting symptoms in wheat in the variety trial near Chickasha, OK (40 miles southeast of Oklahoma City) now is believed to be caused by bacterial streak (aka black chaff – see pictures below).  Bacterial streak/black chaff is occasionally observed in Oklahoma but typically is not widespread or severe.  This disease is more severe in warm (80 F or so) and humid climates or in wheat grown under irrigation, and often appears after an event such as a late freeze or other event that can cause wounds to facilitate entrance of bacteria into plants.  Lesions on leaves initially appear water-soaked but become elongated dead bands and streaks as time proceeds.

Bacterial streak lesions on leaves initially appear water-soaked but become elongated dead bands and streaks as time proceeds.

Bacterial streak lesions on leaves initially appear water-soaked but become elongated dead bands and streaks as time proceeds.

These dead areas tend to be more common on leaf “bends” where dew forms to enhance infection.  Symptoms on heads and on the stem immediately under the head include dark discoloration, and awns typically show a dark banding.These symptoms often can be confused with leaf spotting caused by the fungi Septoria (Septoria tritici blotch) or Stagonospora (Stagonospora nodorum blotch).

Symptoms on heads and on the stem immediately under the head include dark discoloration

Symptoms on heads and on the stem immediately under the head include dark discoloration

Bacterial streak/black chaff is seed transmitted, so grain from a badly infected field should not be kept for seed wheat.  There are no commercial seed treatments available, and although varieties vary in reaction to this disease, no resistant varieties are known in Oklahoma where bacterial streak/black chaff is not commonly widespread.  This disease may be occurring in other parts of Oklahoma this year, but will be difficult to discern from all the other factors that contribute to general browning and leaf spotting including other diseases (tan spot, septoria, etc), freeze, and drought.

Bob Hunger
Extension Plant Pathologist

Jeff Edwards
Small Grains Extension Specialist

Awns affected by bacterial streak/black chaff typically show a dark banding

Awns affected by bacterial streak/black chaff typically show a dark banding

Wheat disease update 18 May 2013

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist

Oklahoma:

Wheat in southern/southwestern Oklahoma is maturing and will speed up with the warmer (>90 F) over the last couple of days.  In central Oklahoma, around Stillwater and to the north, wheat is just finishing or has just past flowering and kernel development is starting.  As you head to northwest Oklahoma, wheat also is in late flowering or has just finished flowering.  I’m not sure about out toward the panhandle but know there is not much wheat that will be harvested as you move west of Woodward and Buffalo.  I’ll be taking a trip to the panhandle the end of the coming week and will report more after that trip.

Disease-wise, not a lot changed over the past week in Oklahoma.  Leaf rust remained practically absent although infections in the 15-40S range were observed in Jagalene (or Jagger) guard rows in breeder plots at Stillwater.  However, little to no leaf rust was found elsewhere around Stillwater and no reports were observed or reported from north-central and northwestern Oklahoma.  Stripe rust is slight more prevalent.  Several “hot spots” were noted around trials at Stillwater and occasional “stripes” (but not hot spots) were noted at field days west of Enid, north of Ponca City, and north of Stillwater.  Leaf spotting diseases, barley yellow dwarf, and wheat streak mosaic (WSM) are the most commonly observed diseases in samples seen at field days and submitted to the Plant Disease and Insect Diagnostic Clinic.  This past week a few samples also tested positive for High plains virus.  Several reports from ag educators, consultants, and growers have indicated that WSM has devastated wheat in fields in northern and western Oklahoma.  In all cases where I talked to the person, there was an indication that volunteer wheat was involved either in the field or adjacent to it.

Reports/excerpts of reports from other states:

Arkansas – Dr. Gene Milus, (Professor/Small Grains Pathologist, Univ of Arkansas, Fayetteville, AR) 17-May-2013:  Visited plots at Kibler near Fort Smith today. Wheat is in soft dough. Stripe rust is still active. Leaf rust was present at mostly low levels. Also Septoria, bacterial streak, powdery mildew, and Stagonospora on flag leaves depending on the line. Most lines in the variety test had resistance to most or all of the above diseases. Weather is hot and humid. Plenty of soil moisture.

Kansas – Dr. Erick De Wolf (Professor/Small Grains Extension Pathologist, Kansas State Univ, Manhattan, KS) 17-May-2013:  Stripe rust continues to be reported at low levels in Kansas this week with new finds in Sedgwick, Kingman, Sumner, and Pratt counties. The wheat in this area of the state is still heading or flowering. Generally, only trace levels could be found in these fields.  Tom Maxwell, Central Kansas District agent, reported finding low levels of stripe rust in Saline County on May 17. The wheat there is generally in the early heading stages.  I have found a few fields and a demonstration plot in Pratt County where the disease is at high enough levels to justify a fungicide application. This area of the state has received more rain than others in recent weeks and some fields in Pratt County have good yield potential. The affected varieties included Everest and Armour, which were found to be susceptible in 2012. A lot of wheat in this area of the state is struggling with continued dry weather.

I encourage farmers to carefully check fields for symptoms of disease. Fields where stripe rust can be readily found on the flag leaf (one lesion every 2-3 feet) will likely benefit from a fungicide application. The wild card on this decision is the weather.  Low temperatures in the upper 60’s are generally thought to be suppressive to stripe rust development. High temperatures in the upper 80’s or above for several days in a row also tend to suppress stripe rust. But if temperatures in that range last only last a few days or so, followed by cooler weather, stripe rust can resume activity.

Wheat disease update 11 May 2013

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist

Oklahoma:  As you move from southern to northern/northwestern Oklahoma, wheat ranges from past flowering to flowering to heads emerging/approaching flowering (depending on variety and planting/emergence date).  It is highly variable.  Weather continues to be cool and moist except in southern, western and northwestern Oklahoma where it continues to be dry.

There were no reports of leaf rust over the last week in Oklahoma, but reports of stripe rust increased.  However, none of these stripe rust sightings indicated a widespread, severe outbreak anywhere in the state.  Bryan Vincent (Crop Consultant – northern Oklahoma) reported seeing strip rust on Everest wheat just west of Orienta, OK (about 40 miles west of Enid).  Dr. Brett Carver (OSU Wheat Breeder) reported in his visit early in the week to his breeder nursery at Lahoma (north central OK – 10 miles west of Enid), that, “35 swipes, just one 1″ sporulating Yr lesion at Lahoma, f-3. Otherwise nothing. Will keep looking.”  On Friday (10-May) at the Lahoma field day in the variety trial, I found an occasional active stripe in expected varieties (Pete, Garrison, Iba, Everest, and Armour), but these stripes were rare – only one or two per plot.  However, our weather over the last couple weeks and the near forecast is for weather favorable for stripe and leaf rust, so we may begin to see more of these rust diseases.  Powdery mildew continues to be found but I have not seen it yet on flag leaves or even F-1 leaves.  Leaf spotting diseases (tan spot, septoria, stagonospora) are more severe in Oklahoma than typical but vary by location.  For example, Dr. Jeff Edwards (OSU Smalll Grains Extension Agronomist) indicated that at his variety trial at Chickasha, leaf spotting was widespread, severe, and was on the flag leaves of specific varieties in the trial.

Regarding viruses – barley yellow dwarf is commonly observed at all locations, but is not associated with severe stunting indicating a later infection.  Numerous reports have been received and many samples have now tested positive for wheat streak mosaic virus from many areas of Oklahoma.  None of these samples have tested positive for either High plains virus or Triticum mosaic virus.

Reports/excerpts of reports from other states:

Arkansas – Dr. Gene Milus, (Professor/Small Grains Pathologist, Univ of Arkansas, Fayetteville, AR) 10-May-2013:  Most wheat has flowered or is flowering now. I found a low level of leaf rust at Rohwer in the southeast corner, and this is the first confirmed leaf rust here. Stripe rust is still active. Bacterial streak showed up on several varieties in the variety test. Leaf blotch is moving up the plants. There is abundant soil moisture across most of the state.

Kansas – Dr. Erick De Wolf (Professor/Small Grains Extension Pathologist, Kansas State Univ, Manhattan, KS) 11-May-2013:  The wheat is heading and flowering in southeastern and south central Kansas this week.  Wheat in central Kansas is mostly in the boot stages of development with the most advanced fields beginning to head this weekend. The wheat in southwestern KS continues to struggle with drought and freeze damage and growth stage varies widely among fields.

Disease scouting this week suggests the risk of severe rust epidemics remains low in Kansas this year.  I had a few more reports of trace levels of stripe rust in southeastern KS where the wheat is flowering. The levels of stripe rust are very low at this time.  Temperatures are forecast to reach the upper 80’s early next week with low temps at or above 60 F. Temperatures in this range often slow the development of stripe rust but farmers in this areas should monitor the disease carefully.

I was able to find a single pustule of leaf rust in Stafford county Kansas this week, but the wheat at this location was thin from recent dry conditions.  I suspect the leaf rust will not increase rapidly at this location.  Other fields that I checked in southwest KS (Finney and Kiowa counties) show significant drought stress and no sign of rust.  In south central and central Kansas (Pratt, Reno, and McPherson counties), the wheat is in better condition with thick canopies and good moisture recently.  I found no leaf rust, stripe rust or stem rust in these areas; however, several fields had moderate levels of powdery mildew. Symptoms of barley yellow dwarf remain low or absent in all fields I have check to date.

Stripe rust on wheat at Lahoma

Stripe rust on wheat at Lahoma

Wheat disease update 04 May 2013

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Wheat Pathologist

Oklahoma:  Over the last week I, Nathalia Grachet (OSU graduate student), and Brian Olson (OSU A&P) extensively looked at wheat around Stillwater, and in central (Minco, Apache), southwestern (Granite), and north central (Lahoma) Oklahoma.  Additionally, OSU Wheat Breeder Brett Carver examined his plots at numerous locations in central, southwestern OK as well as at Stillwater, and Dr. Art Klatt (OSU Wheat Geneticist) examined trials around Stillwater and Perkins.  Wheat in southwestern Oklahoma was damaged from drought and freeze, and little disease was discernible.  Wheat in southwestern Oklahoma (where it was possible) appeared to be at various states of head emergence, and in a few cases was just starting to flower.  In central OK, wheat was in various stages of heading.  Around Stillwater, wheat was just starting head emergence, while at Lahoma wheat was mostly just approaching GS 10 (boot stage).  However, there seems to be quite a bit of variability regarding stage of maturity depending on variety and planting date.

No leaf rust was observed at any location.  The “hot spot” of stripe rust we found at Minco is still active, but my previous update incorrectly identified ‘Duster’ as the variety with the most severe stripe rust.  Actually that was ‘Garrison’.  Stripe rust also was on Duster but not to the same severity nor was significant stripe rust on the flag leaves of Duster.  This is the only location where we observed significant stripe rust.  We also observed powdery mildew and leaf spotting on lower to mid leaves at many locations.  Primarily the leaf spotting appeared to be septoria/stagonospora with some tan spot mixed in, and as expected is usually somewhat more severe in no- or low-till fields.

Barley yellow dwarf was commonly observed at many locations with variable severity, but it was often difficult to differentiate damage between BYD, freeze, and drought.  Wheat streak mosaic also was observed across the areas examined (see photo below).  An increasing number of samples from around western OK have kept Jen Olson (Plant Disease Diagnostician) busy.  Most of these samples have tested positive for BYDV, WSMV, or both, but no high plains virus or Triticum mosaic virus has been detected.  This includes the Stillwater area where I have never before (since 1982) observed WSM.  Another interesting find here at Stillwater included occurrence of Russian Wheat Aphid, which was confirmed by Dr. Rick Grantham (Director of the Plant Disease and Insect Diagnostic Lab –  photos below taken by Rick).

Wheat showing symtoms of Wheat Streak Mosiac Virus. There are no curative sprays for this virus, but it can be avoided by ensuring volunteer wheat and other grasses are dead at least two weeks prior to planting

Wheat showing symtoms of Wheat Streak Mosiac Virus. There are no curative sprays for this virus, but it can be avoided by ensuring volunteer wheat and other grasses are dead at least two weeks prior to planting

Symptoms of Russian wheat aphid feeding

Symptoms of Russian wheat aphid feeding

Russian wheat aphids on wheat

Russian wheat aphids on wheat

Wheat disease update 26 April 2013

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Wheat Pathologist

Oklahoma:  Reports of stripe rust were more common from Oklahoma this past week.  Yesterday (25-Apr) I and Nathalia Grachet (OSU graduate student) looked at wheat in central Oklahoma to the southwest, west, and northwest of Oklahoma City (OKC).  Wheat in this area was variable, but mostly around GS 10 (boot stage) to heads just emerging.  Fields where freeze damage occurred showed a wide range of tiller maturity.

Fields around Apache, OK (about 75 miles southwest of OKC) including the variety trial showed light powdery mildew and leaf spotting (tan spot/septoria/stagonospora) with stripe rust found in one field located about 10 miles west of Apache – not severe but the incidence was spread across the field (variety unknown).  On our return trip to Stillwater, we found stripe rust on lower to mid leaves in the variety demo at Minco (about 25 miles southwest of OKC) with the most severe rust on Duster (photo below).  Powdery mildew was severe on lower leaves of the wheat in the field surrounding the variety demo.  No rust was observed at the variety trial at Kingfisher (about 30 miles northwest of OKC), and no leaf rust was found at any stop.  Although not severe, stripe rust also was observed this past week around Stillwater/Perkins by Dr. Art Klatt (OSU wheat geneticist/breeder) and by Mark Gregory (OSU Southwest Extension Agronomist) in the variety trial near Chickasha (30 miles southwest of OKC).   Dr. Klatt also reported severe powdery mildew in his plots near Perkins.  Symptoms indicative of barley yellow dwarf are common around Stillwater and on the trip yesterday, however, freeze damage symptoms make it difficult to comfortably identify BYD without confirmation in the lab.

Stripe rust on Duster near Apache OK on 25 April 2013

Stripe rust on Duster near Apache OK on 25 April 2013