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Wheat Disease Update – 9 June 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

      During the last two days there have been a couple reports of dark wheat heads being observed in fields.  This is a condition call sooty mold (aka black head mold) (Figure 1). These dark heads are the result of saprophytic (living of dead tissue) or weakly pathogenic fungi growing on the dead tissue in wheat heads.  Reports of this have come from Greg Highfill (Alfalfa County Extension Educator in north central OK) and from Brad Secraw (Cleveland County Extension Educator in central OK).  Additionally, I have observed severe sooty mold in some of the trials around Stillwater.

      Sooty mold occurs when wheat has turned but cannot be harvested in a timely manner.  Wet/humid conditions during a delayed harvest will then promote the fungal growth on wheat heads.  Often wheat that has been subjected to a stress such as freeze, root rot, or drought shows a greater severity of sooty mold than if the wheat had been healthy and not stressed.  This is the case in the top photo in Figure 1.  The darker strips of wheat with sooty mold are the variety Pete, which was hit hard by the late freeze in April.  The lighter, more golden colored heads with much less sooty mold are lines in one of Dr. Carver’s nurseries.  These breeder lines were not nearly as affected by the freeze as was the Pete.  Although grain yield from wheat with sooty mold often is reduced, the sooty mold itself is not the primary cause of that reduce yield.  Rather, it was the stress such as a freeze or root rot that was the primary cause of the reduced yield. 

Figure 1. A field view of sooty mold (black head mold) on wheat at Stillwater, OK on June 9, 2021 (top photo). Note the darker appearance of the wheat heads in the alternating long, solid strips of wheat compared to lighter, more golden colored heads in the middle strip. The bottom two photos show wheat heads with sooty mold. [Photo credits bottom two photos – Left photo; Greg Highfill (Extn Educator, Alfalfa County); photo on right; Brad Secraw (Extn Educator, Cleveland County)].

One additional point to be made is that grain harvested from wheat with severe sooty mold may show a condition known as black point (Figure 2).  Black point is a discoloration of the seed (typically the germ end of the seed) resulting either from infection by various fungi that typically are saprophytic but can occasionally parasitize living tissue, or from a combination of abiotic (environmental) conditions that promote the discoloration without the presence of an organism.  Like sooty mold, black point often is observed when freeze damage has occurred or when harvest was delayed and dead tissue in the heads was heavily colonized by fungi that resulted in sooty mold.  Black point in wheat grain can be a grading factor as the discoloration can result in black flecks in flour milled from such grain.  Additionally, if used as seed wheat, kernels with black point can have reduce germination resulting in lower seedling emergence.  Hence, if wheat showing black point is to be used as seed wheat, it is imperative to check the germination of that seed and to use a seed treatment that controls seed and seedling rots.

Figure 2. Wheat kernels with black point. The wheat kernels to the left and right show typical black point. The kernel in the middle is healthy. Ignore the reddish-pink color in the outer kernels as this is from an applied seed treatment.

FINALLY – This likely will be my (Dr. Bob Hunger) last Wheat Disease update as my last day of work is July 9th.  It has truly been a pleasure to send these updates!! I hope all of you have a great harvest this year and even better ones in the future!!!

Wheat Disease Update – 21 May 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

Wheat tours over the last ten days included Kingfisher (Kingfisher County; south central OK), Cherokee (Alfalfa County; north central OK), Alva (Woods County; northwestern OK), Lahoma (Garfield County; north central OK), Morris (Okmulgee County; eastern OK), El Reno (Canadian County; central OK); and Buffalo (Harper County; northwestern OK).  Wheat in these areas is pretty much done with flowering and kernels ranged from just forming to fully formed.  Some varieties in some areas were in the milk stage with some approaching soft dough.

      Diseases at these locations varied considerably but overall, a wider range of diseases was observed.  Some locations such as Cherokee, Alva and Buffalo had relatively light foliar disease incidence with some leaves indicating barley yellow dwarf and wheat streak mosaic (and/or other mite transmitted viruses).  Around Stillwater and at Lahoma, although stripe rust was still prevalent leaf rust is making an appearance (Figure 1).  At others such as Kingfisher, Morris and El Reno, leaf rust could be found but stripe rust seemed to still be more prevalent.  Leaf spot diseases also were observed at most of these locations, but these foliar diseases were not as prevalent as the rusts.

Figure 1. Stripe and leaf rust both observed on wheat at Lahoma on May 13/14. A mixture of stripe and leaf rust (photo on left) compared to mostly all leaf rust (middle and right photos). [Photo credits – Dr. Amanda de Oliveira Silva; OSU Small Grains Agronomist].

Darkened heads were observed at several locations but were most prominent and prevalent at Morris in eastern OK (Figure 2).  Darkened heads like this can result from several causes.  If Septoria and/or Stagonospora are present on lower leaves, these fungi can move up onto the heads and cause a glume blotch that has this appearance.  Another possibility is a bacterial disease called black chaff or bacterial streak (Figure 3).  Black chaff will occur on leaves (Figure 3; photo on left), but also can move onto heads (Figure 3; center photo).  Note on this center photo how the stem (peduncle) immediately beneath the head shows darkened lesions like those on the head.  Finally, awns of heads infected with black chaff often show an alternating pattern of dark and white (Figure 3; photo on right).  Another possible cause of these dark heads is presence of a gene that confers resistance to wheat stem rust.  In this case, the result is not a disease, but rather an association with the presence of that gene.  Regarding the darkened heads observed in the trial near Morris, Dr. Silva and I agree it is most likely the majority of the darkened heads observed likely resulted from freeze damage as many of these heads also were totally or partially sterile (see Dr. Silva’s blog at https://osuwheat.com/2021/05/18/freeze-damage-update/).  However, Septoria/Stagonospora and black chaff also contributed as symptoms of these diseases were observed in the field.

Figure 2. Darkened heads observed on wheat heads in a trial located in eastern Oklahoma near Morris. These darkened heads were caused by Septoria/Stagonospora, black chaff and/or freeze. [Photo credits – Dr. Amanda de Oliveira Silva; OSU Small Grains Agronomist].
Figure 3. Black chaff (bacterial streak) on wheat at Chickasha in 2013. Photo on the left is of a leaf infection; center photo shows darkening of the head and the stem just beneath the head; photo on the right shows the alternating dark and light pattern often seen on awns of wheat heads infected with the bacterium that causes black chaff. [Photo credits: Dr. Jeff Edwards; Oklahoma State University]

A final disease observed this past week was indicated by the sporadic occurrence of white heads in some parts of the field.  Examination of plants/tillers associated with these white/yellowing heads revealed symptoms typical of take all root rot (Figure 4).  However, I am not yet certain that these tillers had take all as symptoms of other root rots also were present.  Hence, samples were brought back to the lab for isolation and identification.  Look for an update on this in my next report but be aware there likely will be root rot showing up in some areas of the state.

Figure 4. Symptoms of take all root rot. White heads (photo on left) as the plants mature often indicate presence of a root rot. Lower, blackened stems and crowns of tillers with white heads resulting from take all root rot (photo on the right).

This next week marks the end of the wheat field days in Oklahoma with four coming next Thursday and Friday in the Oklahoma panhandle.  A complete schedule of the remaining field days can be viewed at: http://wheat.okstate.edu/virtual-plot-tour/2021OSUWheatFieldTours.pdf

Wheat Disease Update – 10 May 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

Wheat tours last week included Homestead (Blaine County; west-central OK), Afton (Ottawa County; northeastern OK), Sentinel and Tipton (Washita and Tillman Counties, respectively; southwestern OK) and Kildare and Lamont (Kay and Grant Counties, respectively; north-central OK).  At Homestead, Dr. Amanda Silva (OSU Small Grains Agronomist) saw primarily tan spot (Figure 1) as this trial was planted in a field of wheat after wheat.  Sentinel was fairly free of foliar diseases, but the trial at Tipton was severely infected with stripe rust.  The incidence and severity of stripe rust at Tipton also was observed by Dr. Brett Carver (OSU Wheat Breeder/Geneticist) who indicated that he saw severe stripe rust in his trials at Tipton as well.  Near Chattanooga OK, also in SW OK, there was a report of stripe rust occurring in wheat heads (Figure 1, center photo and photo to the right).  Over the years, I have occasionally observed this in Oklahoma, and it typically is a signal that stripe rust has been severe.  As far as I know, the grain is not infected, but rather it is the plant tissue surrounding the grain.  These reports of severe stripe rust contrast with what Dr. Silva and I observed at Afton, Kildare, and Lamont where little foliar disease of any type was observed.  We did however see symptoms indicative of barley yellow dwarf at all locations and some indicative of the mite-transmitted virus diseases such as wheat streak mosaic and high plains disease.

Figure 1. Tan spot (photo on left) observed on May 3rd by Dr. Amanda Silva (OSU Small Grains Agronomist) in the variety trial at Homestead, OK in west-central OK. Center and photo to the right show stripe rust that has infected and is sporulating in a wheat head. The photo credit for these two photos goes to Leon Fisher and came to me via Jerry Goodson and Mike Schulz (Station Supt, Altus).

This week will be spent at wheat field days in central, north central, and northwestern OK including trials near Cherokee, Kingfisher, Thomas, Alva, and Lahoma. A complete schedule of the remaining field days can be viewed at: http://wheat.okstate.edu/virtual-plot-tour/2021OSUWheatFieldTours.pdf

Wheat Disease Update – 23 April 2021

This article was written by Dr. Bob Hunger, Extension Wheat Pathologist

      Just a brief update to relay that stripe rust continues to increase across Oklahoma.  Bryan Vincent (Crop Consultant; north-central OK) reported severe stripe rust in “hot spots” on an unknown variety just north of Lamont, OK (Grant County) close to the Kansas border (Figure 1; left photo). In Major County, which is immediately south of Grant County, Josh Coltrain (Winter Wheat Technical Development Lead, Syngenta) reported he had, “found quite high incidence of stripe rust” in Syngenta’s plots near Carrier, OK.  Here around Stillwater, I have observed severe stripe rust in spreader strips of the susceptible variety Pete. These infections stood out because of resistant breeder lines planted immediately adjacent to the strips of Pete (Figure 1; center photo and photo to the right).

Figure 1. Severe stripe rust in a susceptible variety (Pete) planted next to resistant breeder lines in a nursery at Stillwater, OK (photo on the left). The photo on the right shows the severity of stripe rust pustules on an individual leaf of Pete.

      However, the most striking example I have seen of stripe rust in some time was observed by Jeff Wright (Coordinator of Production Operations; OFSS; Oklahoma State University) in an increase field of the old variety Triumph 64 near Perkins (about 15 miles south of Stillwater).  As you can see in Figure 2 (two top photos), much of the entire field (9 acres) appears yellowish.  Examination of leaves reveals severe stripe rust infection associated with yellowing of the leaf (middle photo). The bottom photo in Figure 2 is of Jeff’s tractor after applying a fungicide.  Although the fungicide should protect the green leaves remaining in the field, much of the leaf tissue will be killed from the stripe rust infection.  This is a good example of the importance of applying a fungicide to a susceptible variety sufficiently early to prevent such widespread infection. What and how such a big and uniform infection occurred is puzzling to me, but I suspect that is related to overwintering of the stripe rust fungus in the field.

Figure 2. Severe leaf rust on Triumph 64 wheat near Perkins, OK (about 20 miles south of Stillwater, OK). Top two photos show the yellowish cast to the foliage. The middle photo shows stripe rust pustules associated with severe chlorosis (yellowing) of the foliage. The bottom photo shows Jeff’s tractor after applying a fungicide spray two days ago.

      In other wheat around Stillwater, there continues to be a high incidence and severity of powdery mildew.  Barley yellow dwarf also is easily found in many trials and varieties.  Dr. Tom Royer has sent out an alert about finding English grain aphids around the state.  These aphids also were observed by Bryan Vincent in north-central OK and by me here around Stillwater. Finally, the wheat field days start next week, so observations from those locations will start to appear in subsequent updates. A complete schedule of those field days can be viewed at: http://wheat.okstate.edu/Home/plot-tours/

Wheat Disease Update – 14 April 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

      Last week (08-April) in southwestern OK, Gary Strickland (Jackson County Extn Educator) reported seeing only very little stripe rust, but that tan spot was still present in the lower canopy.  Southwestern OK has been hot and dry, so conditions in that part of Oklahoma have not been at all favorable for foliar disease development.  Also last week, Bryan Vincent (Crop Consultant; north-central OK) reported seeing mostly tan spot and powdery mildew across northern OK, with little to no rust, but some barley yellow dwarf starting to appear as well as aphids.  Greg Highfill (Woods County Extn Educator) also reported heavy tan spot in a no-till, wheat- after-wheat field.

      More recently, although still scattered and light, both leaf and stripe rust (more so stripe) appears to be increasing across Oklahoma.  Lanie Hale (Manager, Wheeler Brothers) sent out the following report.  “Yesterday, Will Bedwell and I scouted 22 wheat fields in southern Major, northeastern Dewey, and northwestern Blaine Counties.  The wheat variety was unknown to us in most of the fields.  In seven of the fields, we found leaf and/or stripe rust in isolated areas, certainly not widespread across the fields.  We found powdery mildew in a few fields, but only where the canopy was heavy and dense.  Septoria and/or Tan Spot was noted on lower leaves in most fields.  Many of the fields had infestations of Bird Cherry Oat Aphids ranging from light to moderately heavy.  We saw several Lady Beetles and larvae in fields; I only saw one mummified aphid indicating not many parasitic wasps are present.  One of the fields had been sprayed over the weekend.  The flag leaf is emerging in most fields we scouted.  We did not scout any field with 100% emerged flag leaves.”

      Yesterday around Stillwater, I saw wheat that ranged from flag leaves emerging to wheat headed, although by far and away most of the wheat was at the boot/pre-boot stage (GS 9 or so).  By far, the most prevalent disease I observed was powdery mildew (Figure 1).  Stripe rust also was present, but at a low incidence.  I also noted quite a few spots or patches of barley yellow dwarf in various trials, but in contrast to other reports, I saw very few aphids.

      Given these reports and observations, it is advisable for producers to start watching their fields closely and prepare for applying a fungicide, especially if growing a variety susceptible to either rust and/or the other foliar diseases.  For more information on fungicides and their use, see OSU CR-7668, which can be found at:  https://extension.okstate.edu/fact-sheets/foliar-fungicides-and-wheat-production-in-oklahoma-march-2016.html.

Figure 1. Wheat leaves observed near Stillwater, OK on 4-13-2021 with powdery mildew and stripe rust (top photo) and with stripe rust (bottom photo).

Perhaps the most striking observation is that wheat streak mosaic (Figure 2) is starting to be reported across both Oklahoma and Texas as a couple of samples have tested positive for Wheat streak mosaic virus in the last week.  For more information on this and other mite-transmitted viruses, please see OSU EPP 7328 that can be accessed at:  https://extension.okstate.edu/fact-sheets/wheat-streak-mosaic-high-plains-disease-and-triticum-mosaic-three-virus-diseases-of-wheat-in-oklahoma.html

Figure 2. Wheat streak mosaic virus has been observed in northwestern Oklahoma and western Texas.

Wheat Disease Update – 30 March 2021

This article was written by Bob Hunger, Extension Wheat Pathologist

Reports of foliar diseases, especially stripe and leaf rust, are starting to increase in southern Texas and around Stillwater. First, here is an update sent out on 24-March by Dr. Amir Ibrahim (Regents Professor & Small Grains Breeder/Geneticist; Texas A&M AgriLife Research). Dr. Ibrahim is finding both stripe rust and leaf rust increasing across southern Texas.

“I visited our small grains trials at McGregor (18 miles southwest of Waco, TX) on March 18, 2021.  Stripe rust (caused by Pstriiformis Westend. f. sp. tritici Eriks.) continues to be active (Figure 1; photo on the left).  Leaf rust (caused by Puccinia triticina Erikss.) is beginning to move to the middle canopy (Figure 1 – photo on the right).”

Figure 1. Stripe and leaf rust observed by Dr. Amir Ibrahim in southern Texas in mid-March.

“We visited the naturally inoculated Rust Evaluation Nursery at Castroville, TX today. The nursery is about 196 miles from Texas A&M University’s main campus in College Station, where we are based.  We also visited our trials at Uvalde, TX today. Stripe rust is not very active at both Castroville and Uvalde. Leaf rust is now picking up, especially at the Rust Evaluation Nursery at Castroville. Stripe rust is very actively spreading at the Agronomy Farm near our main campus in College Station as of our last visit on March 23, 2021. Stripe rust is also active in our trials in Greenville (50 miles northeast of Dallas). No reports yet of leaf or stripe rusts in the Texas High Plains. Leaf rust is also developing in our trials at Wharton (60 miles southwest of Houston).”

      In Oklahoma, both stripe and leaf rust (Figure 2) have been observed in trials around Stillwater and near Perkins (about 15 miles south of Stillwater).  Also recall in my update of 15-March, I indicated seeing powdery mildew, Septoria/Stagonospora (Figure 3) on lower leaves in many trials. These diseases also are present, and with the relatively cool and windy weather in the forecast, I expect the incidence and severity of all these diseases to increase.

Figure 2. Wheat showing pustules of the fungi that cause stripe rust (top two photos) and leaf rust (bottom photo). [Observation & photo credit for middle and bottom photos; George Wallace, Oklahoma State University]
Figure 3. Powdery mildew (upper photo), Septoria/Stagonospora (middle photo), and tan spot (bottom photo credit; Gary Strickland, Jackson County Educator, observed in mid-March).

Wheat Disease Update – 15 March 2021

This article was written by Dr. Bob Hunger, Extension Wheat Pathologist

Although relatively quiet, some wheat diseases have started to appear across Oklahoma over the last week.  For example, around Stillwater I am starting to observe patches of wheat showing symptoms of the wheat soil-borne mosaic (SB)/wheat spindle streak mosaic (SS) complex.  So far, I have observed these symptoms only in susceptible varieties in Dr. de Silva’s variety demo and in my SB-SS nursery.  These virus diseases are not a problem in Oklahoma or the central plains due to effective and durable genetic resistance in nearly all wheat varieties planted in Oklahoma for the last four decades.  However, planting a variety susceptible to either or both of these virus diseases could be an invitation to having an occurrence of these diseases.  It seems as though only far northwest Oklahoma and the panhandle have environments that limit the occurrence of these two virus diseases.

      In trials around Stillwater towards the end of last week, I found sparse powdery mildew and fairly abundant Septoria/Stagonospora leaf spot on leaves of ‘Ruby Lee’ (Figure 2).  This was in Dr. Brett Carver’s dual purpose observation nursery, which is an early planted nursery.  In no trials did I find either leaf or stripe rust, although Dr. Amanda de Oliveira Silva had found both leaf rust and powdery mildew in her demonstration trial in later January before the hard freeze and snow occurred in early to mid-February.

Figure 1.  Wheat showing reaction to the wheat soil-borne mosaic (WSBM)/wheat spindle streak mosaic (WSSM) complex. Left photo:  Wheat breeder line susceptible (left) and resistant (right) to WSBM. Center photo: Symptoms typical of WSBM.  Right photo:  Symptoms typical of WSSM.

Figure 2. Upper photo are symptoms on a wheat leaf indicative of Septoria or Stagonospora leaf blotch found near Stillwater on 13-Mar-2021.  The lower photo is of a wheat leaf with symptoms indicative of tan spot observed in southwest Oklahoma by Gary Strickland, (County Educator; Jackson County), 3-11-2021.

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.”

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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.”