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Wheat disease update – 08 May 2015

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

Oklahoma:

In addition to looking at wheat around Stillwater this past week, I also was at field meetings near Kingfisher (30 miles northwest of OKC), Kildare (10 miles north of Ponca City), and Lahoma (10 miles west of Enid).  Wheat was at full berry to borderline milk.

Stripe rust, leaf rust, and powdery mildew were present at all locations, with stripe rust by far the most prevalent.  Where a fungicide had been sprayed (e.g., in Dr. Jeff Edwards variety trial), the effect was striking in terms of green leaf tissue.  Difference in variety susceptibility to stripe rust was obvious, with Ruby Lee, Garrision, Pete, and Everest being some of the more common highly susceptible varieties.  There also seems to be varieties with high levels of resistance (e.g., Gallagher, Jackpot, etc), and intermediate resistance; however, I’ll wait until I have all ratings in to evaluate this in more detail.

This overhead shot of the Chickasha intensive and standard wheat variety trials illustrates the severity of stripe rust in the region. The intensively managed trials on the left was treated with a fungicide just prior to heading. The standard trial on the right has the exact same varieties but no fungicide. The "middle" replication between the two studies is a border of Ruby Lee that is 1/2 treated 1/2 non treated. Photo courtesy Brian Arnall.

This overhead shot of the Chickasha intensive and standard wheat variety trials illustrates the severity of stripe rust in the region. The intensively managed trials on the left was treated with a fungicide just prior to heading. The standard trial on the right has the exact same varieties but no fungicide. The “middle” replication between the two studies is a border of Ruby Lee that is 1/2 treated 1/2 non treated. Photo courtesy Brian Arnall.

Leaf rust can be found in some varieties at severe levels, but has not increased to a level comparable to stripe rust.  Most commonly, I am seeing it on leaves of varieties that are resistant to stripe rust, but susceptible to leaf rust (e.g., Jackpot).

Barley yellow dwarf also was observed at all locations, but little to no stunting was associated with the BYD, so infection most likely occurred in the spring.

Powdery mildew also was observed at every location, but only rarely was on the flag leaf or heads.

I have not seen any Fusarium head blight, but have had a few reports of it from eastern/northeastern OK.

The diagnostic lab continued to receive samples testing positive for Wheat streak mosaic virus, with several also testing positive for High plains virus (Wheat mosaic virus)  For information on mite-transmitted diseases, I refer you to EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic:  Three Virus Diseases of Wheat in Oklahoma) also available at www.wheat.okstate.edu 

 

Reports/excerpts of reports from other states: 

Kansas Dr. Erick De Wolf (Extension Plant Pathologist); Kansas State Univ, 4-May-2015:  “The past week continued to bring more finds and reports of rust diseases in Kansas. Stripe rust is the primary concern many growers and the disease is now established in many areas of the state.  The disease has moved onto the upper leaves in many fields in the southeastern and south central regions of the state.  The wheat in these areas of the state was at or near the heading and flowering stages of growth this past week. Infections on the upper leaves at these stages of growth places the crop at risk for severe yield losses.  Stripe rust was found at low levels in many counties in the central and north central regions.  The disease was also reported at low levels in western Kansas.  At this point the stripe rust was primarily low to moderate incidence (1-5%) and mostly restricted to the lower leaves of many fields in the central and western regions.  However, the weather this past week was very conducive for stripe rust and the disease may soon increase to damaging levels in more areas.

The risk of yield loss in these areas depends heavily on weather over the next 2 weeks.  Stripe rust is favored by temperatures in the 40-60’s, frequent rain or heavy dew deposition. The progress of stripe rust often slows when nighttime temperatures exceed 60 degrees F.  The weather outlook for the central region indicates that rain is likely this week but also suggests low temperatures may slow further disease development. Temperatures in north central and western Kansas may be more conducive for stripe rust.  So far the stripe rust is most severe on varieties known to be susceptible to the disease but there are some early indications of unusual disease reactions on varieties previously thought to be resistant.  I will gather more information and come back with reports soon.

Leaf rust has also been detected at trace or low levels at many of the same locations as stripe rust (Crawford, Clay, Ness, Riley, Saline, and Sumner counties).  These reports are significant because the presence of leaf rust increases the risk of disease related yield loss in the state. Many of the popular varieties grown in the state are susceptible to leaf rust and finding the disease prior to flowering indicates the leaf rust may also cause problems in some areas.  To date the leaf rust appears to be most common on varieties with the Lr39/41 resistance gene (Fuller and WB 4458 for example).

 

TEXAS:  Dr. Clark Neely (Small Grains & Oilseed Extn Specialist; Texas A&M AgriLife; College Station; 7-May-2015:  “I spent the past several days attending wheat field days in northeast Texas. Stem rust was found in susceptible soft wheat varieties in Ellis County. After fading away for the most part from warmer temperatues, stripe rust was re-establishing itself on flag leaves of susceptible varieties in due to the cooler, wet weather affecting the region. Most wheat in the region is in the milk-soft dough stage. Leaf rust was moderate to severe on susceptible lines at Howe, TX including TV 8861, however, leaf rust was much lighter at Leonard and Farmersville, TX locations.”

 

Georgia:  Alfredo Martinez, John Youmans, James Buck; University of Georgia; 6-May-2015:  “Leaf rust infections have been observed in commercial wheat fields in Southwest Georgia (Seminole Co. Mitchel Co. Taylor Co.). The incidence of leaf rust seems to be localized and the severity was low. Stripe rust was confirmed in northwest GA (Floyd Co.). The incidence and severity was minor. Commercial fields surveyed near UGA College of Agricultural and Environmental Sciences Research Station in Plains, GA and around the UGA CAES Bledsoe Farm near Griffin GA yielded no stripe, leaf rust or stem rust infections.  Low rust and powdery mildew on wheat in GA was probably due to the use of resistant varieties and /or timely applied fungicides. However, for a second year in row, Fusarium Head Blight (FHB/Scab) incidences were numerous (albeit not as prevalent as in 2014), in some fields the severity was high. Surveyed fields in Sumter Co. had severity of 50%-60%. Environmental conditions at the time of wheat flowering provided conducive conditions for FHB infections especially in the southernmost part of the state. Stagonospora spot blotch and tan spot were observed throughout the state and seemed more prevalent than previous years.”

Wheat leaf rust

Wheat leaf rust

Wheat stripe rust

Wheat stripe rust

Wheat disease update – 01 May 2015

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

Oklahoma:  This past week I spent in fields/nurseries around Stillwater and also attended field days in central OK (Caddo Cnty) and southwestern OK (Jackson Cnty).  Most of the wheat I saw was at ¼ to nearly full berry.  Foliar diseases have definitely increased.

Around Stillwater, powdery mildew is evident on the lower leaves in my fungicide trial (approx. 25% severity).  In the variety demo strips at Stillwater, I can find severities >65% on lower leaves.  However, stripe rust is still the most evident foliar disease with mid-canopy leaves of susceptible varieties often completely or nearly completely infected.  Flag leaves of susceptible varieties around Stillwater are beginning to show stripe rust pustules, but that is still not uniform in all fields/locations.  Also this past week I started to see leaf rust pustules developing on lower leaves; I only occasionally saw pustules on flag leaves with the exception of ‘Jagalene’, which was at 90% or so.

In central OK I saw mostly the same thing.  At the variety trial near Kingfisher (Kingfisher Cnty), disease was surprisingly light with stripe rust the most evident.  Near Apache OK (southern Caddo Cnty), disease was more prevalent with stripe rust the most severe.  Varieties resistant to stripe rust but susceptible to leaf rust (e.g., ‘Jackpot’ were beginning to show more leaf rust pustules).  Tan spot also was evident at this variety trial as it is a no-till field.

This overhead shot of the Chickasha intensive and standard wheat variety trials illustrates the severity of stripe rust in the region. The intensively managed trials on the left was treated with a fungicide just prior to heading. The standard trial on the right has the exact same varieties but no fungicide. The "middle" replication between the two studies is a border of Ruby Lee that is 1/2 treated 1/2 non treated. Photo courtesy Brian Arnall.

This overhead shot of the Chickasha intensive and standard wheat variety trials illustrates the severity of stripe rust in the region. The intensively managed trials on the left was treated with a fungicide just prior to heading. The standard trial on the right has the exact same varieties but no fungicide. The “middle” replication between the two studies is a border of Ruby Lee that is 1/2 treated 1/2 non treated. Photo courtesy Brian Arnall.

In southwestern OK (near Altus, OK), stripe rust was severe (90% or so) on the flag leaves of susceptible varieties such as ‘Ruby Lee’, ‘Everest’, and ‘Garrison’.  Varieties with resistance to stripe rust such as ‘Gallagher’ and ‘Billings’ showed little sporulation but loss of some green tissue due to the hypersensitive reaction (HR).  ‘Greer’ showed no stripe rust and no dead tissue due to the HR.  Here again, a variety like Jackpot showed no stripe rust, but leaf rust was at a moderate level.  An interesting observation was made by Dillon Butchee (Helena Chemical Rep), who noticed stripe rust sporulating inside the glumes of susceptible varieties, which I have seen only occasionally in Oklahoma.

In more northern OK, Greg Highfill (Extension Educator, Woods Cnty – near Alva, OK) indicated he has seen small amounts of stripe rust in the border of the test plot near Alva.  Although temperature is increasing, the forecast for next week is highs only in the low to mid 80s with Tuesday-Thursday being rainy again.  These temps will be lower in northern and northwestern OK.  Hopefully the rain will continue, but these conditions will favor continued spread and increase of particularly leaf rust.  For most of Oklahoma, I believe wheat is past or quickly approaching the point where a fungicide can no longer be applied.  For a discussion of this, see “CR-7668 Foliar Fungicides and Wheat Production in Oklahoma – April, 2015,” which is available at www.wheat.okstate.edu.

Stripe rust at Alva, Oklahoma. Photo courtesy Greg Highfill

Stripe rust at Alva, Oklahoma. Photo courtesy Greg Highfill

 

Finally, the diagnostic lab continues to receive samples testing positive for Wheat streak mosaic virus.  For information on mite-transmitted diseases, I refer you to EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic:  Three Virus Diseases of Wheat in Oklahoma) also available at www.wheat.okstate.edu

Reports/excerpts of reports from other states: 

Nebraska:  Dr. Stephen Wegulo (Extension Plant Pathologist); Univ of Nebraska, 28-Apr-2015:  “Yesterday I surveyed wheat fields in south central and southeast Nebraska.  Stripe rust was widespread (prevalence of >70%) in the southernmost tier of counties.  Incidence ranged from about 15% to > 80% in some fields.  Severity was mostly trace to low (< 10%), although a few isolated leaves had >50% severity (see attachment).  Growth stage was mostly Feekes 6; in a few fields it was Feekes 6 to 8, and in two irrigated fields wheat was in the boot stage.  These two irrigated fields apparently had been sprayed and there was no stripe rust in them, but I was able to find some leaves on which stripe rust development was stopped by the fungicide spray.  There was severe winter kill in some fields to the extent that the wheat was sprayed with herbicide and another crop will be planted.

Last week (Thursday and Friday) I surveyed wheat fields in the southern and northern Panhandle of Nebraska (the far northwest of the state) and in southwest and west central Nebraska.  I found no foliar diseases, but there was root rot in one field that also had some winter kill in the northern Panhandle.  In the west central part of the state, there was severe winter kill in some fields (see slide #3 in the attachment).  Growth stage ranged from Feekes 5 in the Panhandle to Feekes 5 to 6 in the southwest and west central parts of the state.”

Wheat disease update – 23 April 2015

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

Oklahoma:  Again, a cool and moist week in Oklahoma with rain and cool temperatures in the forecast through the weekend.  Wheat is mostly at flowering around Stillwater but by early next week will likely be past flowering.  From what I hear across the state, wheat is quickly approaching, at, or will be quickly past flowering (depending on what part of the state, when planted, and how much drought stress was endured).

Around Stillwater there has been an increase in stripe rust and powdery mildew (especially stripe rust).  Leaf rust also has increased, but not to the same extent (incidence or severity) as stripe rust.  Dr. Brett Carver (OSU Wheat Breeder) indicated he saw significant stripe rust in his nurseries at Lahoma (north-central OK).  Gary Strickland (Jackson County Extn Educator) also has observed an increase in stripe rust (and to a lesser extent, leaf rust) in far southwestern Oklahoma.  My impression is that stripe rust has activated again with the cool and wet weather, and continues to spread across Oklahoma.  This Thursday and Friday there will be field days in central Oklahoma, so look for a more extensive report next week.

To the south of us in Texas (far southern Texas), Dr. Amir Ibrahim (Professor, Small Grains Breeder/Geneticist; Texas A&M AgriLife Research; College Station, TX) has indicated in breeder nurseries near Castroville, TX, that there is a mixture of stripe rust, leaf rust, bacterial leaf streak and some septoria.  This has occurred because of back-and-forth switching between cool and warm temperatures mixed in with lots of rain.  To some extent, this also has occurred across Oklahoma during April.

Mite-transmitted viruses also are prevalent in Oklahoma this year.  Yesterday when in nurseries here at Stillwater I noticed occasional trapped heads scattered throughout the field.  In observing these in the lab using a dissecting scope, I found wheat curl mites associated with these trapped heads.  Although only sporadic around Stillwater, the Diagnostic Lab has received multiple samples that they confirmed for presence of Wheat streak mosaic virusWheat mosaic virus (High plains virus), and/or Barley yellow dwarf virus.  This includes samples from Grady, Noble, Grant, Texas and Woods Counties.  I would refer you to EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic:  Three Virus Diseases of Wheat in Oklahoma) available at http://osufacts.okstate.edu for more information on these mite-transmitted viruses.

 

Reports/excerpts of reports from other states: 

Kansas Doug Shoup (SE Area Crops/Soil Specialist) & Erick DeWolf (Extn Plant Pathologist), Kansas State University, 22-Apr-2015:  “Stripe rust has been found in several fields of wheat in southeast , south central, and north central Kansas. Given the forecast of cool and relatively wet conditions for the next seven days, this is a potentially significant situation for fields anywhere in Kansas planted to varieties susceptible to stripe rust. Intensive scouting of fields should begin now.”  [This was the first paragraph of their report, which can be found at:

https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=532

Wheat disease update – 17 April 2015

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

Oklahoma:  This past week has been wet and cool across most of Oklahoma, which has greatly helped the wheat but also should lead to more foliar diseases – especially stripe and leaf rust.  Around Stillwater, we have not seen a big increase in stripe rust yet, but can find many leaves beneath the flag leaf on which there are actively sporulating pustules.  There also are leaves on which the black spore structure stage of stripe rust has appeared (called the telial stage – see photo – note actively sporulating pustules towards the base of the leaf).  Typically this indicates the disease is “shutting down,” which it was prior to this week.  However, with the cool and wet weather since Monday, there likely will be a “reactivation” of stripe rust – especially given that cool and wet weather is forecast for the next 5-10 days as well!

The black spore structure stage (telial stage) of stripe rust. Note actively sporulating pustules towards the base of the leaf.

The black spore structure stage (telial stage) of stripe rust. Note actively sporulating pustules towards the base of the leaf.

I get the impression from talking to Aaron Henson (County Educator; Tillman County) as well as other growers and consultants around the state that this is similar to what they are seeing.  Wheat seems to range from boot to heads emerging, so if you are contemplating applying a fungicide to protect a promising wheat yield, I suggest it be done soon.  Remember, GS 10.5 (heads fully emerged but not yet flowering) is the cut-off for applying fungicides for wheat foliar diseases.  That point likely is not far away for much of southern and central Oklahoma.  It likely is a bit farther away for northern and northwestern Oklahoma, but it is much better to apply a fungicide a little early rather than after the flag leaf is infected.

Most of the samples that came into the Diagnostic lab last week tested positive for wheat streak mosaic (WSM), including three from the panhandle.  However, there is nothing that can be done about WSM at this point.  I would refer you to EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic:  Three Virus Diseases of Wheat in Oklahoma) available at www.wheat.okstate.edu for more information on these mite-transmitted viruses.

Reports/excerpts of reports from other states:

Colorado  Dr. Scott Haley (Professor & Wheat Breeder, Colorado State University) 16-Apr-2015:  “FYI, stripe rust was confirmed for a field site near the Denver International Airport in Colorado this week. Infection was moderate but cool wet weather we are experiencing now could cause this to increase. This is pretty early for stripe rust sightings in eastern Colorado.”

Northwestern / north central Oklahoma wheat update – drought, greenbugs, and freeze

Dr. Hunger traveled southwest Oklahoma this week, so I made a trip out Hwy. 60 yesterday to evaluate freeze injury and assess the overall condition of the wheat crop in northwestern and north central Oklahoma. Last week’s warm temperatures and wind have taken their toll on wheat in Kay, Grant, and eastern Garfield Counties. It is not too late for rain to save a partial wheat crop in these areas, but the “full yield potential” ship sailed long ago. Wheat sown behind summer crops is the hardest hit, and wheat in these fields could best be described as yellow and thin. If the weather turned and we received rain in the next week, I would predict that yield potential in these fields would still only be around the 15 bushel mark. Without rain, subtract around 15 bushels. Wheat planted behind summer fallow has held on a little longer, but is clearly showing the signs of extreme drought stress. If we receive rain in the next week (and continue to see rain) these fields could still make 20 – 30 bushels per acre. In the absence of rain in the near future, they will be 10 bushels per acre or less.

Wheat in the Lamont test plot was approximately GS 7 - 8. Flag leaves were rolled and plants were starting to abort tillers.

Wheat in the Lamont test plot was approximately GS 7 – 8. Flag leaves were rolled and plants were starting to abort tillers.

 

In addition to drought stress, we found freeze injury and greenbugs at Lamont. I was a little surprised to find freeze injury and even more surprised to find the greatest injury in the later-maturing varieties. We split several stems of early varieties such as Ruby Lee and Gallagher and did not find any injury. These varieties would have likely been at approximately GS 7 – 8 when the freeze occurred. We found significant injury in later-maturing varieties such as Endurance, but these varieties were likely only GS 6 – 7 when the freeze occurred. Conventional wisdom regarding freeze injury is that the more advanced the variety, the greater the likelihood of freeze injury. After seeing the same phenomenon last year (i.e. the greatest injury in later maturing varieties) I am changing my thinking on freeze injury and now say that all bets are off when it comes to freeze injury in drought stressed wheat.

Freeze injury was greatest in late-maturing varieties at Lamont.

Freeze injury was greatest in late-maturing varieties at Lamont.

 

Overall wheat condition started to improve around Nash and Jet, I would say that much of the wheat in this area is CURRENTLY in fair to good condition. I emphasize the currently in the previous sentence, as the only difference between wheat in the Cherokee area and wheat to the east was about one week’s worth of moisture. Some terrace ridges had already started turning blue and moisture was starting to run out. Without rain wheat in this area will rapidly deteriorate from good to poor. One consistent theme throughout the day was greenbugs. Many sites had evidence of parasitic wasp activity (i.e. aphid mummies), but the presence or absence of parasitic wasp activity varied field by field. Dr. Royer has indicated that greenbugs still need to be controlled in drought stressed wheat. If parasitic wasps are active, the best decision is to let them do the aphid killing for you. If no mummies are present, then insecticide control could be justified. The only sure way to make this determination is to use the glance-n-go sampling system.

 

Greenbugs were alive and well at Lamont

Greenbugs were alive and well at Lamont

Parasitic wasps were keeping greenbug populations under control in this field

Parasitic wasps were keeping greenbug populations under control in this field

Active and parasitized greenbugs on the same plant

Active and parasitized greenbugs on the same plant

 

Similar to Lamont, we found freeze injury in the Cherokee and Helena areas. Many of the worst looking fields (extensive leaf burn) had only superficial injury and should recover if moisture allows. Conversely, some plants that showed no outward signs of freeze injury had injured heads within.  Most fields I surveyed had less than 10% injury, but one field was a complete loss. On the surface the 10% injury field and 100% loss field looked the same, so I cannot over stress the importance of splitting stems. I have received a few additional reports of freeze injury from Kay County this morning, so it is important for producers throughout northern Oklahoma to evaluate their wheat on a field by field basis.

 

Plants that look healthy on the exterior could contain damaged wheat heads

Plants that look healthy on the exterior could contain damaged wheat heads

A closeup of the damaged wheat head from the picture above

A closeup of the damaged wheat head from the picture above

Although freeze injury to plant tissue in this field was severe, the wheat heads were mostly left unscathed

Although freeze injury to plant tissue in this field was severe, the wheat heads were mostly left unscathed

A closeup of a head from the freeze-injured wheat shown above. Although tissue damage is severe, the growing point and wheat head are still viable

A closeup of a head from the freeze-injured wheat shown above. Although tissue damage is severe, the growing point and wheat head are still viable

A final note on freeze injury. Freeze injury appeared to be worst in no-till fields and in areas where residue was heaviest. Based on my observations, this was not due to winterkill or poor seed to soil contact. My best explanation is that the lack of soil cover in conventional till fields allowed stored heat to radiate from the soil surface and slightly warm the crop canopy. The insulating effect of residue in no-till fields did not allow radiant heating to occur. Given the pattern of freeze injury in fields with varying degrees of residue across the field, I feel pretty confident in this analysis of what occurred.

Please use the comment section to share pictures or descriptions of wheat in your area.

Wheat disease update – 09 April 2015

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

Oklahoma: On April 6, I traveled a route from Clinton (85 miles west of OKC) in west central Oklahoma going northeast through Custer County to Kingfisher (40 miles northwest of OKC) and then to Marshall (35 miles west of Stillwater). Although there was some good wheat on this route (e.g. the variety trials at Kingfisher and Marshall), it is posed to decline quickly unless rain is received. Most of the wheat I looked at in Custer County northeast of Clinton was small and fields were terribly dry. Wheat in this area seemed to be at GS 6-7 and I’m guessing was planted quite late due to the dry fall. The most common problem I saw were greenbug, especially in Custer County. However, as the photos show, there were many mummies present indicating the population should be crashing shortly. I also saw some stripe rust but only an infection here and there. Around the variety trial at Kingfisher, wheat was mostly around GS 9 and I saw no aphids or disease. At Marshall, wheat was at GS 8 and there was some stripe rust but at a low incidence.

Greenbugs and mummies in Custer County, Oklahoma

Greenbugs and mummies in Custer County, Oklahoma

On April 7, I traveled to Frederick in south central OK looking at wheat along the way. At a variety demo 20 miles west of OKC right at I-40, I found the wheat at GS 8 with just a little touch here and there of stripe rust. Soil moisture here looked good; this area must have caught a decent rain in the last week or so. The same could be said at another variety demo straight south about 15 miles south at Minco. Here the wheat in the field surrounding the demo was at GS 9, there was good soil wetness, and the wheat looked good. I did not see any rusts or powdery mildew, but there were occasional BYD spots. Further southwest near Apache (30 miles north of Lawton) wheat was at GS 9-10 and looked very good in the variety trial as well as in fields. However, some leaves were beginning to roll and the need for moisture to continue the crop was evident. I didn’t see any aphids or diseases in wheat west of Apache, but I the variety trial just south of Apache I found some stripe rust and greenbug; both at a very low incidence.

Wheat stripe rust

Wheat stripe rust

The rest of this trip was spent with Aaron Henson (Extension Educator, Tillman County) and Mark Gregory (Area Extn Agron Spec – SW Oklahoma) looking at wheat in Tillman County. Wheat in this area was mostly at GS 9-10 with awns occasionally just emerging from the boot. Some fields we visited were dry and impacted by drought, while others looked good but needed another drink soon. A few fields were outstanding and had good soil moisture. One field in particular was the best wheat I have seen since 2012. It was a field of Ruby Lee that was at GS 10 and had been sprayed on 15-Mar because of reports of severe stripe rust in the area and in northern Texas to the south. A 20 ft strip of unsprayed wheat was left on the outside of the north and west side of the field because of power lines and wind. This strip served as an excellent control to indicate the effect of the spray. The line between sprayed and not- sprayed was visible from the road and even more evident in the field (see photos). Within the not-sprayed strip, flag leaves were green with leaves beneath the flag hit hard with stripe rust (see photos). The field was sprayed a second time on 05-Apr because it has such good potential. Leaves in the sprayed area are completely green. I have difficulty explaining the complete lack of stripe rust on the flag leaves in the not-sprayed area. Likely the flag leaves were not yet emerged at the time of the first spray and then conditions after spraying did not allow spread of stripe rust to them. However, in talking to Aaron and Mark it seems there were conditions after the 15-Mar spraying that would have been conducive for spread of stripe rust. At any rate, this is an excellent example of how a timely spray did a tremendous job of protecting yield potential.

Stripe rust – note yellow cast to wheat in foreground that changes to deep green about halfway into phot

 

Signs of stripe rust were present in the lower canopy, but stripe rust was not present on flag leaves

Signs of stripe rust were present in the lower canopy, but stripe rust was not present on flag leaves

Fungicide-treated Ruby Lee in the same field as above photos

Fungicide-treated Ruby Lee in the same field as above photos

 

Other diseases observed across the Oklahoma include wheat streak mosaic, which has been detected in samples from several places including around Stillwater and from Noble County just north of Payne County (where Stillwater is located). However, I have not received indication yet of severe WSM; part of this may be related to the drought in western OK where WSM is typically more common. Recently samples from northwestern OK are beginning to come into the diagnostic lab, but results from some of those samples are still pending.

 

Reports/excerpts of reports from other states:

Texas Dr. Charlie Rush (Professor, Texas A&M AgriLife Research, Amarillo) 3-Apr-2015: “I haven’t checked all fields as closely as those around Bushland but there are a lot of GB and Russian wheat aphids as well as bird cherry.  Russian seems predominate in my fields.  We sprayed last week but will likely sustain significant yield loss from not spraying earlier.  I suspect we’ll start getting lots of calls and samples that end up being BYDV, although some WSM is also showing up.  Mild winter with more moisture than last few years has resulted in a crop that has looked very promising up to now but without good subsoil moisture what we had in the upper layers of the soil profile is disappearing fast and obvious symptoms of drought are beginning to appear.”

Wheat disease update – 16 March 2015

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

Oklahoma:  The leaf rust I saw around Stillwater in February seems to have “died out.”  The cold weather we had from late February into early March killed the lower leaves where leaf rust was active and conditions did not allow spread to younger leaves.  Dr. Brett Carver (OSU Wheat Breeder) confirmed this to me this morning as he indicated late last week he did not see any rust (leaf or stripe) around Stillwater or at his nurseries in Lahoma and Marshal.  This also is the case for northern and northwestern OK, as well as for KS (see Dr. De Wolf’s observations under “Other States” below).  Dr. Tom Royer and I visited variety trials at Cherokee and Alva last week.  No foliar diseases were observed but Dr. Royer did find a small greenbug colony on wheat in the field surrounding the Alva trial.  However, with mild temperatures and moisture predicted for the coming week and with inoculum to the south of us in Texas and southern Oklahoma, foliar diseases should be increasing in incidence and severity across central and northern OK.

Leaf and stripe rust are active in Texas (see Dr. Ron French’s observations below), and southern and central Oklahoma.  Mark Gregory (Area Extn Agron Spec – Duncan, OK) has reported seeing both leaf and stripe rust (but more stripe rust) across much of south-central and southwestern OK – especially around Grandfield, OK located north of Wichita Falls, TX.  Similar reports have come from Aaron Henson (Extn Educator; Tillman Cnty) and Gary Strickland (Exten Educator; Jackson Cnty).  Incidence has ranged from scattered to many “hot spots” of stripe rust, and from light to intermediate incidence of leaf rust.

Some of these fields (especially if it is a susceptible variety) will merit an early application of fungicide to curtail foliar disease activity (especially the stripe rust).  Be aware that applying a fungicide now will not last the entire season, and a second application toward head emergence also may be needed if weather continues to be favorable for foliar diseases.  For an early season application I recommend using a full rate (as opposed to a half rate) of a less expensive fungicide because there is so much time left in the growing season.  Then a later season application with a more expensive fungicide may or may not be needed.  Also be sure to not exceed the maximum amount of fungicide applied and to rotate chemistries to prevent resistance. Also consider your variety.  A variety like Ruby Lee that has good yield potential should be protected from early and late stripe or leaf rust, but a variety such as Duster may show some leaf rust early but still has good resistance to this rust.  However, stripe rust on Duster may merit control.  ALSO, in no-till fields watch for incidence of diseases such as tan spot, septoria, and powdery mildew as these diseases likely will be more common in fields with wheat residue and may merit an early season fungicide application.

Reports/excerpts of reports from other states:

Texas  Dr. Ron French (Ast Prof & Extn Plant Pathologist, Texas A&M AgriLife Extension Service, Amarillo) 9-Mar-2015:  “Last week, I was visiting the lower Coastal Bend of Texas (around Kingsville/Corpus Christi) and the Lower Rio Grande Valley of Texas (along the southernmost part of the Texas-Mexico border area). In Weslaco (Hidalgo County, Lower Rio Grande Valley), I visited sentinel plots (21 lines-winter wheat, spring wheat, barley…).”

“In Weslaco (March 4), Puccinia graminis f. sp. tritici, the causal agent of stem rust, was found on leaf tissue only, at trace levels to 1% severity in six 6 lines including  Morocco,  Marvelous, Kyto (CI 8250) and Line B (1% severity). Last year, stem rust was first observed on Siouxland, Panola, and  Morocco but observations were done the week of April 7, 2014.”

“Stripe rust (March 3)on wheat was observed  in 5 lines, ranging from  trace levels in Siouxland  to 25% incidence and 40% severity on Sisson.  Leaf rust was only observed at trace levels in lines such as Siouxland, Panola, and Sisson.  Powdery mildew was only present in the lower canopy of barley  Hypana, Morex DPH, and Hyproly.  Some wheat was already in the boot stage (Morocco, Line B).”

“Last year, dry conditions (little or no rain) were present in this area when stem rust was first observed. This year has seen more rain during the past three weeks, with temperatures ranging from as low as 38° F to as high as 84°F (lower on average for that area). With rain and warmer weather expected this week, disease pressure may be more conducive to seeing more disease development for all rusts.”

“No stem rust was observed in wheat in  the lower coastal bend around Kingsville, approximately 110 miles north of Weslaco. Fields did have stripe rust (up to 20% severity) but had already been sprayed with a fungicide and trace levels of leaf rust could also be observed.”

Kansas  Dr. Erick De Wolf (Prof & Small Grains Extn Pathologist, Kansas State Univ) 11-Mar-2015:  “We did some scouting for rust diseases near Manhattan (Northeastern KS).  We were checking on research plots where rust had been noted last fall but were unable to detect leaf rust in these plots so far this spring.  We noted severe tip die-back of the leaf tissue in these plots and suspect that this winter injury has removed much of the leaf rust from this location. Bethany Grabow, Ph.D candidate with KSU detected a trace of leaf rust on wheat in an adjacent field.  Incidence of disease was <0.01% with only a few pustules detected. This wheat was planted later than the aforementioned plots and did not experience the winter injury to the leaf tissue.  We also noted small colonies of aphids in the research plots with each colony having 3-5 aphids a few winged aphids were also observed near the colonies. We will continue to monitor the diseases this spring and provide more updates soon.”

Wheat leaf rust

Wheat leaf rust

Wheat stripe rust

Wheat stripe rust

Wheat disease update – 27 February 2015

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

Oklahoma:  As indicated in the Texas reports below, both leaf rust and stripe rust are present across Texas with stripe rust appearing to be the most prevalent and severe.  This also seems to be the case in Oklahoma – at least across central to southern Oklahoma.  John Fenderson (Monsanto) indicated yesterday that on a recent trip he took across central to southern Oklahoma he saw “clean” wheat around Chickasha but along highway 70 going west to Frederick he saw lots of stripe rust and some leaf rust.  In a few places he saw the ground colored orange from stripe rust spores indicating a stripe rust “hot spot.”  In fields such as this (especially if there are many hot spots), application of a fungicide to control the stripe rust should be considered.  In addition to helping to control the stripe rust, there could be the benefit of also limiting leaf rust, powdery mildew and possibly tan spot/septoria.

Around Stillwater, I have not seen much change since two weeks ago.  I have not confirmed any stripe rust, but have seen leaf rust.  However, we have been mostly quite cold with only slight moisture but stripe rust may also be starting.  I will wait until it warms up a bit before I look again.

Wheat leaf rust

Wheat leaf rust

Wheat stripe rust

Wheat stripe rust

Reports/excerpts of reports from other states:

Texas 

Dr. Amir Ibrahim (Prof, Small Grains Breeding and Genetics, Texas A&M AgriLife Research) 26-Feb-2015:  The wheat crop in South Texas is at now at Feekes stages 5-6 [start of node elongation/first node detectable at base of tiller] depending on the line.   Leaf Rust (P. triticina) is spreading in our trials at College station (Brazos County) and both ‘Baldwin’ catch plot and ‘TAM 110’ are 100S.  As for stripe rust (P. striiformis), the ‘Sisson’ catch plot is 70S whereas the ‘Patton’ border is 100S.  It is noteworthy that we reported stripe rust on Patton near Ennis (Ellis County) on January 29, 2015.

Leaf rust is easy to find, but severity is very low at Bushland (Potter County) in Texas High Plains and Chillicothe (Hardeman County) in Texas Rolling Plains.  Unconfirmed reports also indicated spread of stripe rust in Brady (McCulloch County) in the heart of the state. Reports also indicated that ‘Redhawk’ was especially susceptible there and that some producers are already applying fungicides. Both leaf and stripe rusts are also present in Wharton County in South Texas.

If conditions continue to prevail, we can have significant leaf and stripe rust levels compared to last year, in my opinion.

Dr. Ron French (Ast Prof & Extn Plant Pathologist, Texas A&M AgriLife Extension Service, Amarillo) 25-Feb-2015:  Update on wheat rust in Texas- some commercial fields.  Leaf rust had been reported in Texas in fall 2014 as far north as Hansford County (Texas Panhandle, bordering the Oklahoma Panhandle) and throughout NW Texas, especially the Texas Panhandle. In early winter 2015, leaf rust was still found around the Amarillo area. This winter in Amarillo, we have had temperatures as low as 3°F  and will still be as low as 12°F and not much higher than the mid- 50s F for the next week, including snow.  In some cases when temperatures have dropped this much, some fields with trace levels of leaf rust no longer exhibited leaf rust for a while, whether that meant inoculum did not survive, was not active, or had new inoculum come in to that field. I visited some random fields today in the Amarillo area and was not able to find any leaf rust. This does not mean that leaf rust is not present but that it may be present at really low trace levels.

Last Wednesday, February 18, I did find leaf rust in one wheat field in Wichita County at trace levels in very few plants and only in the lowest two leaves. The biggest wheat in that field was at Feekes 4. Wichita County is in the Texas Rolling Plains and borders Clay, Wilbarger, and Archer Counties in Texas, and Tillman and Cotton Counties in SW Oklahoma. With high temperatures expected not to be higher than 63°F and as low as 25°F for the next seven days, could disappear, as observed in previous years when leaf rust was first observed in mid-to-late March.

Unlike 2014, no leaf rust has been observed so far in the lower Coastal Bend of Texas around Kingsville and Corpus Christi by this time. Some days have been cooler than normal and they have had more rain than in some previous years.

Stripe rust has been present as far west as Tom Green County in west Central Texas, where the city of San Angelo is located. Stripe rust was first observed at the very end of January and beginning of February. Stripe rust levels were significant in lower leaves only and the ground was covered in orange spores. A few fields that were sprayed with Tilt on February 16th had taken advantage of the fact that topdressing of nitrogen was being done on the wheat. Within a week, fields looked great and new growth looks “excellent” (probably a combination of topdressing, moisture from overhead pivot irrigation, root growth, and the fungicide application). At time of spraying, the wheat was fully tillered. Some varieties with some level of stripe rust include TAM 113, Coronado, Greer, Redhawk, Cedar, and TAM 304.

The farthest north I have seen stripe rust is in Wichita County at low trace levels, on February 18th.  The biggest wheat in that field was at Feekes 4. Although normally dry, this area may be getting some snow and rain in the next week or so, so there could be an increase in inoculum. But since temperatures are expected to range from 25° to 41°F on the low side, and between 32-63°F on the high side for the next seven days, this may not be conducive to stripe rust increase or establishment. Time will tell. Other fields in that area have not had stripe rust so far from what I gathered today.

Other locations with stripe rust include fields around De Leon, in Comanche County, located in Central Texas. The application Tilt in February is not uncommon in some locations in southern Texas as powdery mildew can be an issue. This year, applications of Tilt have occurred due to stripe rust concerns and in many cases, taking advantage of top dressing of nitrogen on wheat.

Wheat disease update – 11 February 2015

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

Oklahoma: Reports of diseases in Oklahoma have been sparse (as expected for this time of year) but certainly more numerous than last year when drought curtailed foliar diseases.  Yesterday (10-Feb) I found wheat leaf rust at a low, but consistent level in guard strips of Jagalene planted around a large wheat breeder nursery here in Stillwater.  Susceptible-type pustules were on lower leaves at 15-25%.  As temperature increases and with moisture this rust will increase and spread.

Gary Strickland (Extension Educator – southwest Oklahoma) indicated to me that he had heard reports of some leaf rust in Tillman County and also has seen a few pustules here and there on wheat in Jackson County, but nothing severe.  He has seen no powdery mildew and no root rots to speak of.  He also indicated there were a lot of acres of “little wheat” with some looking good if moisture had been received but that the southwest OK was quickly drying out.

Symptoms of wheat soilborne mosaic/wheat spindle streak mosaic (SB/SS) have shown up in Dr. Edward’s variety demonstration as well as in my SB/SS evaluation nursery, but symptoms are not yet striking as the flush of spring growth has not yet started.

Wheat soilborne mosaic virus can cause yellowing in the spring in susceptible varieties such as the one on the left.

Wheat soilborne mosaic virus can cause yellowing in the spring in susceptible varieties such as the one on the left.

 

Reports/excerpts of reports from other states:

Louisiana; Dr. Stephen Harrison (Professor; Wheat & Oat Breeder, LSU AGCenter) 3-Feb-2015:  “Stripe rust has been reported in several commercial fields and nurseries around central and northeast Louisiana.”

 

Texas Dr. Amir Ibrahim (Prof, Small Grains Breeding and Genetics, Texas A&M AgriLife Research) 3-Feb-2015:  “Wheat stripe rust found in Texas Blacklands area:  On January 29th, Russell Sutton, Assistant Research Scientist with the Small Grains program at Texas A&M University and our anchor in the northern Blacklands area and northeast Texas, visited our research plots near Ennis Texas. Russell found a small hot spot of stripe rust on the susceptible variety ‘Patton’ that we use as a spreader. The spot was about three feet in diameter and the lower leaves where heavily infected. The wheat appears to have completed the tillering stage and ready to begin jointing.  Russell will return in two weeks and collect some spores and look for more infection sites.

Wheat disease update – 31 October 2014

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

Oklahoma:  We’ve not seen any diseases so far this fall around Stillwater, but we have been relatively dry and much of the wheat was not planted until the past couple of weeks.  Mark Gregory (Area Extn Agron Spclt – southwestern OK) indicated to me earlier this week that he has not seen or heard any reports of leaf rust or other diseases.  However, Bryan Vincent (Crop Scout – NW/NC Oklahoma) sent me some photos of leaf rust pustules he found in several fields around the Aline-Helena area (30-40 miles northwest of Enid in north-central OK).  The pustules were extremely sparse and found only in very early planted wheat.  Bryan also reported seeing some light tan spot infections.  Leaf rust also has been observed in Kansas, Colorado, and Nebraska (see reports below), and stripe rust has been reported in Wyoming, Montana and the PNW.

Fall infestations of leaf rust rarely carryover to the spring and generally do not warrant treatment. Monitor fields and consider a split fungicide application in the spring if heavy foliar disease is still present at Feekes GS 6 - 7

Fall infestations of leaf rust generally do not warrant treatment. Monitor fields and consider a split fungicide application in the spring if heavy foliar disease is still present at Feekes GS 6 – 7 in early March

When leaf rust occurs in the fall in Oklahoma, the question arises regarding the value of spraying to control that rust.  Fall-infected leaf rust plants typically have yellowed lower/older leaves with rust pustules, but the youngest 2 or 3 leaves are green and healthy.  As temperature drops through November and December, the older rust-infected leaves die and new infections are greatly slowed and inhibited.  Grazing also helps to remove these leaves and increase air circulation and drying that are conditions less favorable to spread of the disease.  Given these considerations, spraying to control leaf rust in the fall is of limited value.  The primary concern with fall infections of 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 these fields through the winter and early next spring is recommended to determine if a split application of a fungicide is merited to control the rust (and also possibly tan spot, septoria, and/or powdery mildew) in the early spring.

Reports/excerpts of reports from other states:

Kansas (Dr. Erick De Wolf, Extn Plant Pathologist, Kansas State University) 27-Oct-2014:  Wheat Leaf Rust Update in Kansas:  Planting of the winter wheat crop in Kansas is well underway. Farmers are reporting that wheat has emerged and is looking good in many areas of the state. Wheat planting on some farms was delayed by a late soybean harvest this fall, but these acres should be planted soon.

I was checking wheat this week in Manhattan (Northeast KS) and found leaf rust in some research plots.  This wheat was sown about 2-weeks prior to the optimal planting date but well within the normal planting range for wheat production in the state.  The leaf rust was not difficult to find with disease incidence near 5% some plots. The severity was 2 percent or less on most of the infected leaves. This level of fall infection of leaf rust is common in Kansas; however, 60% of the time cold temperatures and leaf desiccation during the winter months will eliminate the disease in many fields.

Ned Tisserat, retired plant pathologist from Colorado State University, also reported leaf rust in Northeast Colorado this past week. So it is possible that leaf rust is active in other areas of Kansas as well.  I will be checking other locations for leaf rust in Kansas this coming week and let the group now what I find.

Nebraska (Dr. Stephen Wegulo, Extn Plant Pathologist, Univ of Nebraska) 27-Oct-2014:  On Friday last week, Oct 24, I answered a call from a crop consultant who told me there is leaf rust in several wheat fields in the Panhandle of Nebraska.