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Wheat disease update – 16 April 2016

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

OklahomaI had limited trips outside of Stillwater this past week, and only was able to contact one County Educator before writing this today.  Wheat around Stillwater is mostly at various stages of head emergence.  I did see a few anthers on scattered heads, but not many.  By contrast, Aaron Henson (County Educator; Tillman County in south-central OK) indicated wheat in his area is mostly at flowering.

During this past week, I had several calls about spraying wheat with a fungicide.  Although rust (stripe and leaf rust) didn’t appear to increase this past week, conditions reverted to being more favorable for stripe rust development with rainfall, increased dews, and favorable temperature.  With more rains and cool temps in the forecast, stripe rust could “reactivate” again, and leaf rust will start to come into the picture.  Wheat is now at the point where it will quickly move past the stage (the start of flowering) where it can be sprayed with most fungicides.  As far as I know, all wheat foliar fungicides (with the exception of Prosaro) must be applied prior to the start of flowering (Feekes’ growth stage 10.5).  Prosaro can be applied through growth stage 10.5.1, which is when flowering is just starting (anthers emerged mostly from the middle of heads).  Be sure to read all labels regarding a fungicides use on wheat.  There also are varying pre-harvest intervals (PHIs) required for the various fungicides, and often the length of time from heading to harvest can be short in Oklahoma.  So, be aware of these PHIs, and spray accordingly.

Active sporulation of stripe rust still can be found around Stillwater and the surrounding area.  Stan Fimple (County Educator, Pawnee County just to the northeast of Stillwater) sent me the following photos showing active stripe rust.  The photo on the top shows an actively sporulating “stripe” of strip rust (yellowish-orange in color), whereas in the photo on the bottom in the “stripes” you can see dark, blackish specks (teliospores) starting to appear.

 

Active spore stage of stripe rust

Active spore stage of stripe rust

Survival spore stage of stripe rust

Survival spore stage of stripe rust

 

Other than this, I have seen scattered leaf rust pustules on lower leaves around Stillwater, and powdery mildew also has become more apparent around Stillwater and at Lahoma as reported by Dr. Brett Carver (OSU Wheat Breeder).  However, both of these diseases are at low levels on lower leaves but with coming rain and cool temperatures both (especially leaf rust) could continue to increase on the upper canopy.  Around Stillwater, barley yellow dwarf spots continue to be observed but the aphids are now gone or at least in much lower in frequency.  If heavy rains come over the next 3 or so days, I would imagine aphid populations will be mostly eliminated.

Finally, I want to raise awareness once again to Fusarium head blight (scab) of wheat.  When wheat flowers it is susceptible to infection by the Fusarium fungus that causes scab.  That time is quickly approaching. Occasionally Oklahoma has problems with this disease, typically more so in eastern/northeastern Oklahoma than through the central and western parts of the state.  However, scab was severe across the state for a couple years around 2010 and there also was some reported last year.  For more information on scab, please see PSS-2145 (Fusarium Head Blight (Head Scab) of Wheat:  Questions & Answers) and PSS-2136 (Considerations when Rotating Wheat Behind Corn) that can be found at: wheat.okstate.edu.  An additional resource is the Fusarium Head Blight Prediction Center at http://www.wheatscab.psu.edu/.  At this site you can read commentaries submitted by specialists from each state but more importantly see if weather conditions in your area have been conducive to development of FHB.  The site is easy to use and especially may be beneficial in helping make fungicide application decisions.

Reports/excerpts of reports from other states:

Louisiana:  Dr. Stephen Harrison, Wheat & Oat Breeder, Louisiana State University, Apr 15, 2016:  My research associate (Kelly Arceneaux) is at the Rice Research Station in Crowley (Southwest) Louisiana rating plots today.  We plant a double-headrow set of a number of nurseries every year for disease screening at this location in collaboration with Don Growth (rice pathologist).  This site is inoculated with scabby corn but is not misted due to the abundance of humidity and free moisture at this site.  Nurseries include: Statewide Variety Trial, Uniform Southern Soft Red Winter Wheat Nursery, Uniform Southern Scab Nursery, Sunwheat, GAWN.  Kelly reports that stem rust is heavy and widespread at this site.  Leaf rust is moderate and scab is at an intermediate level, which is good for distinguishing lines.  The earliest plots are starting to mature, probably just past soft dough, while the latest lines are just past heading or not vernalized and not going to head.  We only received about 50% of our normal vernalization hours this winter and quite a few lines in the statewide variety trials will not be harvested due to vernalization issues.

Nebraska:  Dr. Stephen Wegulo, Extn Plant Pathologist, University of Nebraska, April 14, 2016:  “On Friday April 8, Jenny Rees, UNL Extension Educator, found trace amounts of stripe rust in a wheat field in Nuckolls County in south central Nebraska.  Earlier this week, samples from several wheat fields in Banner County submitted to the lab of Dr. Bob Harveson (Extension Plant Pathologist) at UNL’s Panhandle Research and Extension Center in Scottsbluff were positive for stripe rust and leaf rust.  This week on April 12 and 13 I surveyed wheat fields in the southernmost tier of counties in southeast, south central, and west central Nebraska.  Dry weather which has prevailed over the last two weeks or so stopped rust development.  I did not find rust in any of the fields I visited in the southernmost tier of counties.  Several fields showed symptoms of stress from lack of moisture.  Today I looked at research plots at Havelock Farm here in Lincoln (Lancaster County) and at the Agricultural Research and Development Center (ARDC) near Mead (Saunders County, about 35 miles north of Lincoln).  I found a few hot spots of stripe rust at Mead (see first attachment), mostly on the lower leaves.  I also found trace levels of leaf rust at Mead (second attachment).  Powdery mildew was the predominant disease at Lincoln and Mead, but I also saw significant levels of Septoria tritici blotch in one research field at Mead.  Wheat growth stage across the state ranges from Feekes 5 and 6 (most fields) to Feekes 7 in some irrigated fields.”

South Dakota:  Dr. Emmanuel Byamukama, Extension Plant Pathologist, South Dakota State University; Apr 13, 2016:  “Several winter wheat fields in central South Dakota were scouted yesterday for stripe rust. One field originally found with stripe rust last week was the only one we found with stripe rust. Stripe rust was found on old/dying leaves and some of the leaves had teliospores, indicating the source of this rust would have been from overwintered stripe rust in South Dakota.”

 

Wheat disease update – 02 April 2016

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

Wheat has advance in maturity across OK this past week flag leaves definitely are emerging around Stillwater.  From reports I’ve received I believe across the state wheat ranges from flag leaves emerging to heads starting to emerge (although wheat in far northwest OK and the panhandle may not be quite as far along).  I didn’t hear specifics but was told that freeze damage has been observed around Kingfisher in central OK.  With frost/freezing temps again last night, additional damage is possible.  Drought, although not as bad as last year, also is creeping back into the picture.  One producer from southwestern OK indicated to me that “leaves are rolling-up at 2 o’clock in the afternoon.”  I didn’t see any wheat that looked stressed, but in several locations had to dig 4” or more to find moist soil.

In my trips this past week to central OK (Watonga) and to more north-central OK (Blackwell), I could find stripe rust, but it doesn’t appear to me that it had advanced (become more severe).  In fact, Zack Meyer (Extn Educator; Kingfisher Cnty) sent me the following photo that shows the telial spore stage of the stripe rust fungus forming on wheat leaves.  Look closely at the photo and you can see minute yellowish-orange pustules of stripe rust also present on the leaves (especially the greener leaf).  The telial stage is considered more of a survival spore stage and indicates that stripe rust is encountering unfavorable conditions and starting to shut down.  Although this is good news, stripe rust can quickly “reactivate” if favorable temperature and moisture are resumed.

Telial/uredinial pustules of the stripe rust fungus. Zack Meyer; Extn Educator; Kingfisher Cnty

Telial/uredinial pustules of the stripe rust fungus. Zack Meyer; Extn Educator; Kingfisher Cnty

 

Unfortunately there also is a lot of active stripe rust still in the state as I have had numerous calls from across OK to discuss spraying options, and Greg Highfill (Extn Educator; Woods Cnty) sent me the following photo showing moderate/severe and active stripe rust on wheat in northern-central OK.

 

Photo credit:  Greg Highfill - Extn Educator; Woods Cnty in northern-central OK

Photo credit: Greg Highfill – Extn Educator; Woods Cnty in northern-central OK

 

Reports/excerpts of reports from other states:  No reports from Texas, but did hear the following from Kansas and Nebraska.

Kansas:  Dr. Erick DeWolf; Extn Plant Pathologist; Kansas State University; Manhattan, KS; Apr 1, 2016:  “The Kansas wheat crop is progressing rapidly through the jointing stages of development in much of the state.  Wheat in the Southeast portion of the state is at or fast approaching flag leaf emergence.  The crop is generally considered to be two or three weeks ahead of schedule.

Scouting reports indicate that stripe rust is becoming established in the 2016 wheat crop.  This past week, stripe rust was reported in many counties in central and eastern Kansas.  The disease is still at low levels in most fields with a few exceptions in Southeast Kansas.  This early establishment of stripe rust increases the risk of severe yield loss and growers should continue to monitor the situation carefully.  If weather conditions become favorable, the disease could spread rapidly from the lower leaves, where it is now established, to the upper leaves that are critical for grain development.  Leaf rust is still active in the western tier of counties bordering CO but remains a low levels in most fields.  Powdery mildew is severe in some fields in central and eastern Kansas.”

3image003

 

Nebraska:  Dr. Stephen Wegulo; Professor/Extn Plant Pathologist; University of Nebraska-Lincoln; Lincoln, NE, KS; Mar 31, 2016:  “Yesterday March 30, 2016: Jennifer Rees, UNL Extension Educator, found trace levels of actively sporulating leaf rust in wheat fields in Nuckolls County in south central Nebraska.  Nuckolls County is in the southernmost tier of counties that border Kansas.  She did not find actively sporulating stripe rust; however, in one field there was evidence of stripe rust that was active last fall.”

 

Colorado:  Dr. Kirk Broders; Ast Professor; Colorado State University; Ft. Collins, CO; Mar 29, 2016:  “As I mentioned last week stripe rust is now present in eastern Colorado with a confirmed report of stripe rust in the Prospect Valley region northeast of Denver. We have received several reports of stripe rust from that same region. This past week was windy with some precipitation in this area of Colorado, so spores were spread but there was limited moisture to promote additional infection.  There is rain in the forecast for this coming week and the rain is certainly needed for the wheat, but also will provide a favorable environment for stripe rust to increase because temperature is supposed to be staying in the 50s-70s for the days and 20s-40s at night. If you already have noticeable levels of rust in your field you may want to consider including a fungicide at tillering (GS 4) or when you make your herbicide application. If you do not currently have rust in your fields or in your region, I would recommend waiting until closer to flag leaf and monitor the spread of stripe rust in the state.  CSU Extension specialist Wilma Trujillo was able to examine wheat in the southwest part of the state near Lamar, where stripe was present last fall. We examined these leaves and found no evidence stripe rust was able to overwinter in this region of the state. It is still early in the season, but there is certainly the possibility for stripe rust to become a serious problem in the state again this year. There are also the threat of leaf rust we should not forget about. Leaf rust has been present in western Kansas for the last 2 weeks and has likely moved into eastern parts of the state. I have not received in specific reports, but would appreciate you feedback if you have observed either stripe rust of leaf rust in you fields.

Wheat disease update – 19 March 2016

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

Oklahoma:  This past week I looked at wheat around Stillwater as well as in central OK (Blaine County NW of Oklahoma City; Kingfisher just NW of OKC; Apache in Caddo County SW of OKC), and in SW OK around Altus.  I saw wheat as far along as approaching flag leaf emergence to at growth stage 6-7.  The more advanced wheat typically was planted relatively early and not grazed.  Everywhere I was had sufficient moisture, although areas in southwestern and western OK were getting to a point where some rain definitely would be beneficial.  In addition to my observations, I’ve received numerous reports that I’ll summarize here.

At nearly all the places I stopped, I observed varying levels of stripe rust, leaf rust, aphids, and powdery mildew, with powdery mildew being by far the least prevalent.  Stripe rust typically was scattered across fields, but there were some significant hot spots.  In some fields (for example the variety trial at Kingfisher) I saw no stripe rust.  Greg Highfill (Extn Educator, Woods County) and Darrell McBee (Extn Educator, Harper County) sent me the photo below showing stripe rust they found this past week.  They indicated the stripe rust was scattered and not common, but this does mean that spores are present in the field and will increase with favorable (cool and wet) weather.  They also indicated finding a little powdery mildew.  I also heard reports of severe stripe rust in susceptible varieties such as Pete, Garrison, and Everest.

 

Stripe rust in northwestern Oklahoma - Photo courtesy Greg Highfill and Darrell McBee

Stripe rust in northwestern Oklahoma – Photo courtesy Greg Highfill and Darrell McBee

More severe hot spots of stripe rust were reported by David Nowlin (Extn Educator; Caddo County), who sent the following photo of stripe rust on ‘Pete’, which is highly susceptible to stripe rust.

Stripe rust in Pete in Caddo County - photo courtesy David Nowlin

Stripe rust in Pete in Caddo County – photo courtesy David Nowlin

 

Similar reports regarding stripe rust were made by Dr. Brett Carver.  He also has reported seeing considerable chlorosis (yellowing) often with the lack of sporulation.  I saw the same type of yellowing with no sporulation at Kingfisher yesterday (see photo below).  I’m not sure of the cause of this yellowing, but I don’t believe it to be from rust or other foliar diseases because it is widespread in its distribution on lower leaves.  Perhaps it is the result of the environment.

Yellowing in wheat at Kingfisher

Yellowing in wheat at Kingfisher

In no-till fields near Altus and Apache I saw striking tan spot on lower leaves along with numerous pseudothecia of the tan spot fungus on the wheat residue in the field.  Near Altus, this was combined with stripe rust presence such as described above.  In such a case, applying a fungicide early to catch both of these diseases should be considered, especially if the field at this point has a good yield potential.  For more information to help make this decision, see OSU CR 7668 available at www.wheat.okstate.edu

tan spot

tan spot

 

Reports/excerpts of reports from other states:  

Texas : I’ve only received two reports from Texas this past week.  One is from a former student that now lives in the Weatherford, TX area.  He indicates that stripe rust is in the area.  The other report is from David Nowlin (Extn Educator, Caddo County), who indicates a colleague of his located near Denton, TX sent him the following report on 15-March.

“We’re getting hammered with strip and leaf rust as well as powdery mildew on our varieties down here in Denton, TX. We’re just a little further ahead of you. Wheat is not as far along as we normally see.

Kansas:  Dr. Erick DeWolf; Extn Plant Pathologist; Kansas State University; Manhattan, KS; Mar 19, 2016: “The wheat crop is growing rapidly throughout Kansas. The crop in the more advanced fields are approaching jointing in the northwest and are about a week away from flag leaf emergence in the south central and southeast portions of the state.  The crop is generally considered to be about 3 weeks ahead of schedule with respect to normal growth and development. There are multiple reports of leaf rust and stripe rust in Texas, Oklahoma, and other surrounding states.

The Crops Extension team has been busy scouting for disease in recent weeks. We are finding active leaf rust and stripe rust in the state. Leaf rust was reported in west central and northwest, Kansas with most activity in counties bordering Colorado. Low levels of leaf rust were also observed in research plots in Riley County, which is located in northeast Kansas. The winter has been very mild in Kansas and it is very likely that the leaf rust has overwintered in the state. Stripe rust was reported in multiple counties this past week. Stripe rust is generally at very low levels with most activity reported in the southeast portion of the state.  Tan spot and powdery mildew have also been reported in some areas of the state.”

 

 

Wheat disease update – 04 March 2016

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

Oklahoma –  Foliar diseases are becoming active in Oklahoma.  Around Stillwater I have found both leaf and stripe rust, powdery mildew, and septoria.  Incidence/ severity of all these foliar diseases is relatively light, but I am especially watching what happens to the leaf and stripe rust.  The leaf rust pustules are small and on lower/older leaves indicating that leaf rust likely overwintered in Central OK.  The stripe rust pustules were on the upper leaves of ‘Pete’ wheat (see photo) indicating the spores causing these initial infections likely blew up from the south.  With rain and cool wet weather in the forecast, I definitely expect for there to be an increase in foliar diseases.  Around Stillwater, I also have seen quite a few aphids (mostly bird cherry-oat but also a few greenbug) and many lady beetles.  However, no symptoms yet of barley yellow dwarf.

 

Stripe rust on Pete 03/04/2016

Stripe rust on Pete 03/04/2016

Gary Strickland (SWREC Dryland Cropping Systems Spclt – Jackson Cnty) relayed to me that in SW OK he has seen leaf rust in fairly high levels on lower leaves of Endurance and other wheats, and has heard reports of stripe rust but has not seen any himself.

Yesterday I traveled to north-central OK (Alva).  On the way there and while there I visited several fields and found a few very small leaf rust pustules.  Overall the wheat from I-35 over to Alva (Hwy 11) looked good and was greening-up nicely.  Also while in Alva, numerous producers, etc. relayed reports of mostly leaf rust showing up across central OK, such as leaf rust around Geary, OK, etc.

Regarding rust incidence/severity in Texas, I talked to a wheat breeder in Texas last week and he indicated that wheat in southern Texas was showing both leaf and stripe rust but had not yet reached a severe level.  Early next week I’ll be at a meeting of wheat pathologists and should be able to find out more about diseases in Texas.

All these reports indicate the potential for significant foliar disease on the current wheat crop.  Genetic resistance in some of wheat varieties helps protect against the foliar diseases, but fungicides also provide an excellent management tool to protect not only yield, but also quality (test weight).  To help with deciding if and when to apply a fungicide, Dr. Jeff Edwards and I earlier this week updated and revised CR 7668 (Foliar Fungicides and Wheat Production in Oklahoma – March 2016).  It can be found at www.wheat.okstate.edu.  This Current Report discusses the significant aspects related to using fungicides to manage wheat foliar diseases.

One point I want to be sure to emphasize when using fungicides is the importance to not exceed the maximum amount of a fungicide applied to a crop in a single year.  Such a consideration couldespecially be an issue when more than one fungicide application is made.  In many states through the southeastern region of the U.S., two fungicide applications on wheat are more common, with the last application typically targeted toward Fusarium head blight (scab).  In Oklahoma, where scab usually is not a concern, deciding when to make a single fungicide application typically is the only consideration.  However, if you have early disease pressure from stripe rust or have early season powdery mildew, tan spot, or Septoria leaf blotch in no-till fields, more than one application may be needed to adequately manage these diseases.  In these situations, care must be taken to insure label compliance.  For example, if an early application of a generic form of tebuconazole is applied at 4 oz/ac, a subsequent application of any fungicide containing tebuconazole around heading would put you over the 4 oz limit for the crop season.  Thus, be sure to read the label to determine the maximum amount of a chemical that can be applied in a single season and the exact amount of a chemical(s) that is in a fungicide.

South Texas – Amir Ibrahim TAMU Wheat Breeder – The wheat crop in our trials at Castroville and Uvalde, TX is at Feekes stages 5‐10, ranging from the latest winter to the earliest spring types. Growth is very lush and there is no winter kill or frost injury in either winter and spring types. Stripe rust is at 70S, in the medium to upper canopy, on our  ‘Patton’ spreader passes across the field. Stripe rust is about 60S on ‘TAM 110’. ‘Coronado’ is hammered with yellow rust at Castroville.  Stripe rust is more progressed at Uvalde. We have been getting natural and uniform stripe rust infection at Uvalde every year for the last few years. The Texas A&M AgriLife Center at Uvalde sits at the bottom of a valley with constant morning dew that favors infection. Stripe rust has also been found at low levels in the wheat breeding trials near Chillicothe in the Rolling Plains of Texas.

Texas – Dr. John Fenderson – WestBred.  “I saw rampant Stripe in Central TX on Ruby Lee.  I also saw it on sensitive lines from I-20 south anywhere it has rained.  Some spraying has occurred in the Austin area.  I also pulled wheat in the Red River corridor both sides with a lot of stripe on older leaves.  It is just waiting on the right conditions to explode.  I was all the way down in S. TX this week and I did not see stripe on the spring wheat but there was some on Winter wheat around San Angelo etc.”

Wheat disease update – 10 February 2016

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

Since my last report, I don’t believe a lot has changed with the disease situation.  Similar to what I indicated in mid-December, I have continued to find small pustules of powdery mildew and a few scattered leaf rust pustules in rank wheat around Stillwater.  The temperature and weather has been such that these two foliar diseases (powdery mildew and leaf rust) have been able to persist but have not increased in the wheat around Stillwater.  This seems to be the case for southwestern and south central OK as well.

Gary Strickland (Extn Educator & SWREC Dry-land Cropping Systems Specialist; Jackson/Greer Cnty in SW OK) indicated wheat in SW OK is quite a ways behind the rest of the state and mostly is just now establishing a solid root system.  He had sent us a sample last week in which he expected a root rot to be involved, but we were not able to confirm any root rot pathogens.  Gary also indicated that he has confirmed Hessian fly at damaging levels in at least a few fields in Jackson Cnty.  He is going out in the next few days to scout additional fields.  Aaron Henson (Extn Educator; Tillman Cnty in southern OK) indicated wheat in his area varies from quite small to well-established with the majority of the wheat not yet jointing.  He is aware of the earlier reports of scattered stripe rust showing in south-central OK, but has not heard anything to indicate increase in incidence or severity.  For additional information regarding early season foliar wheat diseases and possible control with an early fungicide application please see:

Also around Stillwater, I am beginning to see symptoms indicative of wheat soil-borne mosaic/wheat spindle streak mosaic in areas such as my WSBM/WSSM screening nursery.  At this point, it is somewhat difficult to differentiate between symptoms of WSBM/WSSM and discoloration resulting from cold.  The photo below shows the contrast between a variety susceptible to WSBM/WSSM and a resistant variety, but was taken about 2-3 weeks later than today.  Thus, over the next month as temperature rises and wheat greens up, symptoms will become more striking.  However, nearly 100% of varieties planted across Oklahoma are resistant to both these viruses, so this disease complex has not caused a problem to wheat in Oklahoma (or other states) for many years.  For more information on the WSBM/WSSM complex, go to: https://www.youtube.com/user/OSUWheat/videos and watch the video on “Wheat Soilborne Mosaic Virus and Wheat Spindle Streak Mosaic Virus.”

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.

Powdery mildew

Powdery mildew

Wheat stripe rust

Wheat stripe rust

Wheat leaf rust

Wheat leaf rust

Mature Hessian fly larvae are brown in color and often referred to as flaxseed. Tillers with larvae will not recover and will eventually die and slough off.

Mature Hessian fly larvae are brown in color and often referred to as flaxseed. Tillers with larvae will not recover and will eventually die and slough off.

Is this the year for split fungicide application?

The stripe rust epidemic of 2015 is still fresh on the minds of many wheat farmers. Reports of active stripe rust on wheat in southern Oklahoma has producers now wondering if we are in for a repeat in 2016. While it is too early to tell if environmental conditions will favor a stripe rust outbreak in 2016, having active rust on wheat in the area satisfies at least one of the requirements for an epidemic. Most Oklahoma wheat producers will still be best advised to monitor the situation and make the fungicide decision based on yield potential and likelihood of infection when the flag leaf is emerging. Those with fields already showing heavy infection of foliar disease, however, might also benefit from a two-pass fungicide system. A few talking points and items to consider for those considering a two-pass system are posted below. A fact sheet on the topic of split application of fungicides can be found at www.wheat.okstate.edu

When to apply – The first pass in a two-pass fungicide system should be applied just after jointing. Please note that this is well after topdress nitrogen should be applied. For this and other reasons (see Dr. Arnall’s blog), tank mixing fungicides with nitrogen is generally not a good practice. Remember that the purpose of the early fungicide application is to keep disease in check until you come back with a flag leaf application in April. Going too early can result in too large of a gap between applications and enough time for disease to re-establish. Going too late can reduce the return on investment. Timing is everything with fungicides.

How much to apply – Back in the day, the discussion around split fungicide application centered on half rates for the first application. This recommendation was because of cost savings rather than disease management. The availability of low-cost, generic fungicides, though, has changed our philosophy, and a full rate of a low cost fungicide is the standard for split applications.

Which product to choose – Product choice is at the discretion of the consumer. If you are considering how to best spend your season-long fungicide budget, however, I would strongly recommend saving your “best” and perhaps most expensive product for the flag leaf application.

Watch season-long restrictions – As always, please read labels carefully and make note of season-long application restrictions. You don’t want an early fungicide application to remove the ability to apply your preferred product at flag leaf.

Wheat stripe rust

Wheat stripe rust

This overhead shot of the 2015 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.

This overhead shot of the 2015 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.

Wheat disease update – 15 May 2015

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

Oklahoma:  Early this week I spent time around Stillwater, Lahoma (10 miles west of Enid), and Cherokee and Alva (north-central OK not far from the Kansas border).  Wheat ranged from soft dough around Stillwater to milk at Alva (but quickly approaching dough).  There is a big difference between the wheat in these areas; obviously wheat around Alva suffered more drought stress than Cherokee, which is worse than Lahoma or Stillwater.  However, lots of moisture and cool temperatures are allowing wheat to fill and mature.

As expected, leaf rust has exploded around Stillwater, with susceptible varieties such as OK Bullet at 80-90S.  Leaves are gone on varieties that were highly susceptible to stripe rust, but varieties with stripe rust resistance that are susceptible to leaf rust (e.g., Jackpot, Greer) are now hit hard with leaf rust.

Weather since the middle of April has been reminiscent of the weather in April and May of 2007.  As a result, wheat diseases favored by cool and wet weather are starting to occur with increasing frequency and severity.  These diseases are causing head discoloration, which can be caused by fungi or bacteria.  Around Stillwater and Lahoma, head discoloration due to a bacterium (Xanthomonas) has been observed.  l have had reports of similar symptoms on wheat in southwestern OK, where more rain has fallen then around Stillwater.  This bacterial disease is called black chaff when on the heads and is called bacterial streak when symptoms are expressed on leaves.  The fungi Septoria and Stagonospora also can cause head discoloration, and we have isolated Septoria from several samples during the last week or so.  For a full discussion of the various causes of head discoloration along with pictures, clicking on the following link will take you to the e-Pest Alert sent out in June, 2007.

http://entoplp.okstate.edu/pddl/pddl/2007/PDIA6-17.pdf

Barley yellow dwarf also was observed this past week, but it was not extensive and little to no stunting was associated with the BYD spots indicating infection most likely occurred in the spring.

Purple / yellow leaves associated with barley yellow dwarf

Purple / yellow leaves associated with barley yellow dwarf

 

I have had reports of Fusarium head blight (scab) from southeastern KS, from Arkansas, and from eastern/northeastern OK, but have had no reports from anywhere else in Oklahoma.

Fusarium head blight (head scab) can partially or completely infect wheat heads

Fusarium head blight (head scab) can partially or completely infect wheat heads

Fusarium head blight (head scab)

Fusarium head blight (head scab)

Fusarium head blight infected (top) vs. normal wheat kernels

Fusarium head blight infected (top) vs. normal wheat kernels

 

The diagnostic lab continued to receive multiple samples that tested positive for Wheat streak mosaic virus, with several also testing positive for High plains virus (Wheat mosaic virus) and Barley yellow dwarf 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 http://osufacts.okstate.edu.

 

Reports/excerpts of reports from other states: 

Colorado:  Dr. Scott Haley (Wheat Breeder); Colorado State Univ, 13-May-2015:  “Stripe rust continues to develop in CO. Cool wet weather will likely favor continued development. Wheat is about at the heading growth stage.”

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