About Me

David Marburger

David Marburger

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

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Join us May 12th for the 2017 Lahoma Wheat Field Day!

2017 Lahoma program

Wheat Disease Update – April 22, 2017

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

 

 

Wheat around Stillwater varies but appears to be in various stages of grain formation. Based on talking to a number of producers across northern Oklahoma, wheat heads have fully emerged but has not yet flowered or just beginning to flower. Of course, as you go further west into the panhandle the wheat is not as far along.  I’m not sure as sure about central and southern/southwestern OK, but I talked to one grower yesterday from southwest OK that indicted his wheat varied from starting to flower to kernels being formed. This same grower indicated leaf rust is the most common disease he has seen, and in some fields it is fairly heavy. Across northern OK, producers indicated they are not finding severe levels of foliar disease (primarily rust), but it is there (again, especially leaf rust). Brian Olson (my A&P) spent all of Thursday rating wheat at Lahoma (15 miles west of Enid in northern OK). He indicated there were some hot spots/areas of heavy leaf rust, but that over all, leaf rust was light in the plots he was rating. He also indicated he saw quite a bit of what he assumed to be physiological leaf spot (Figure 1), which we tend to see more of in years with cloudy, cool and rainy weather such as this year. Around Stillwater, I observed both stripe rust and leaf rust, but more leaf than stripe. In some cases, there was a mixture of both rusts on the same leaf (Figure 2).

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Figure 1. Physiological leaf spot observed on wheat in Oklahoma.

 

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Figure 2.  Wheat leaf showing co-infection of leaf rust and stripe rust at Stillwater.

 

Samples testing positive for Wheat streak mosaic virus (WSMV) have continued to come into the Diagnostic Lab. To date, about 45 samples have been tested for WSMV, High plains virus(HPV), and Barley yellow dwarf virus (BYDV). Thirty-two of the 45 were positive for WSMV, 24 were positive for BYDV, and 2 were positive for HPV (co-infection with WSMV). Eleven of the samples were positive for WSMV and BYDV. Most of these samples were received from central and west-central Oklahoma, but it seems the area is expanding. For more information on mite-transmitted wheat viruses such as WSM, please see OSU Fact Sheet EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) available at http://wheat.okstate.edu/wheat-management/insectsdisease/EPP-7328.

 

Reports/excerpts of reports from other states:

Dr. Stephen Wegulo, Professor/Extension Plant Pathologist, University of Nebraska, April 18, 2017:  “Bob Harveson, Extension Plant Pathologist at the University of Nebraska-Lincoln’s Panhandle Research and Extension Center located in Scottsbluff, Nebraska has informed me that he has confirmed stripe rust on wheat plant samples brought today to the diagnostic clinic at the center. The samples are from Sheridan County in the northern Panhandle. Due to the location, we think the stripe rust overwintered. We had widespread stripe rust on fall-planted wheat in Nebraska last fall, and it was most severe in the Panhandle. Currently wheat in Nebraska is mostly at the jointing growth stage. Growth stage in fields I surveyed on Thursday April 13 and Friday April 14 in the southern Panhandle and the southwestern and south central parts of the state ranged from Feekes 6 to Feekes 7. Some fields in the southeast are at Feekes 8.  Almost all wheat fields I looked at during the survey last week looked very green with little or no disease – very low levels of fungal leaf spots in the lower canopy in some fields. The exception was an area in Garden County in the southern Panhandle with fields that are hard-hit with wheat streak mosaic. Gary Hein, Entomologist here at UNL, has told me that this area had pre-harvest hail last year which resulted in volunteer wheat that was not controlled.

 

Dr. Amir Ibrahim, Professor/Small Grains Breeder & Geneticist, Texas A&M AgriLife Research, April 19, 2017:  “I detected wheat stem rust at Castroville, TX on April 8, 2017. Samples sent to Dr. Yue Jin and genotyped by Dr. Les Szabo shows this to be conventional stem rust. Presence of rusted tissue across the plant, especially near the base shows a high probability of overwintering foci, which is uncommon in this region, and might have been triggered by the very mild winter. I visited the site again on April 17, 2017 and detected infections in a 40 X 60 foot area with the original overwintering focus in the middle. I have also found stem rust on susceptible ‘Morocco’ wheat in sentinel plots that are far from the aforementioned foci.”

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Pustules of wheat stem rust in southern Texas (courtesy of Dr. Ibrahim)

 

 

Dr. Erick DeWolf, Extension Plant Pathologist, Kansas State University, April 21, 2017:  “This week has brought more reports of stripe rust in Kansas. Stripe rust can be found in the lower and middle canopy of many fields in central Kansas, but the severity remains low. Stripe rust is more severe in the southeast region of the state and has moved to the upper leaves in some fields. The weather conditions the past 14 days have not favored the rapid spread of stripe rust. Stripe rust is favored by cool, wet weather and temperatures in recent weeks were too warm for the stripe rust fungus to function efficiently. For example, most areas of the state had more than 30 hours of temperatures above 75 F in the last two weeks. Some areas of southwest and south central Kansas had more than 50 hours of unfavorable temperatures. The threat of stripe rust has not passed, however. We know stripe rust is present at low levels in many fields in the state. The disease could increase rapidly if we get into another period of favorable weather with frequent rainfall and temperatures in the 40-50F range at night. I still think there is a moderate risk of Kansas having a serious problem with stripe rust this season.

 

Leaf rust was reported previously in south central and southeastern Kansas. This week brought a few new reports of leaf rust and indications that leaf rust has moved to the upper leaves in few areas. This movement of rust to the upper leaves is important because these leaves provide most of the resources the plants will use produce grain. Any damage done to the upper leaves increases the risk of yield loss.

 

Powdery mildew is becoming severe in fields planted to moderately susceptible and susceptible varieties. 1863, Gallagher, KanMark, LCS Pistol, SY Flint, WB4458, WB-Grainfield, and WB-Redhawk are vulnerable to powdery mildew. In some fields, the powdery mildew has moved to the leaf just below the flag leaf prior to heading. This early establishment of the disease is cause for concern and growers should consider both rust and powdery mildew into their fungicide decisions. Fields with multiple diseases in the middle canopy and those where disease has moved to the upper leaves prior to heading have a more than 80% chance of experiencing a yield loss of >4.0 bu/a.”

Wheat Disease Update – April 14, 2017

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

As expected, over the last week the disease situation has change significantly.  Wheat around Stillwater is mostly nearing complete heading to starting of flowering (Feekes’ GS 10.1 to 10.5.1).  In Jackson County (far southwestern Oklahoma), Gary Strickland (Extn Educator; Jackson County) indicated he has seen wheat as far along as ¼ berry, but most of the wheat is in flowering.  Across southwestern Oklahoma, Heath Sanders (Area Extn Agron Speclst, SW District) indicated wheat he has seen mostly is in the flowering stage.  Wheat at the Lahoma Station (15 miles west of Enid) was mostly between heads emerging to 3/4ths emerged, and according to Greg Highfill (Extn Educator; Woods County) wheat in the Alva area (northwest OK) was mostly just emerging from the boot as of last Tuesday (11-Apr).

 

Around Stillwater, powdery mildew (PM) is the primary foliar disease, but it is staying low in the canopy.  A sparse scattering of stripe rust can be found, but it is extremely sparse.  Leaf rust also is sparse, but is at a higher level than stripe rust.  Barley yellow dwarf (BYD) symptoms are common, but it seems to me there is more yellowing than can be totally attributed to BYD (but I’m not sure of the cause).

 

Gary Strickland indicated that leaf rust is predominate in southwestern OK, but that stripe rust also can be found.  He also is seeing widespread BYD symptoms and higher levels of tan spot (in no-till fields) up higher on the canopy than he has observed in previous years.  Southwestern OK has received more moisture over a longer period of time than the rest of Oklahoma, which explains the higher incidence of foliar diseases.  Gary did not see many aphids over the fall and winter, and so like me, he is surprised at the amount of BYD symptoms.  Heath Sanders indicated he has seen a lot of powdery mildew but again, so far restricted to the lower canopy.  He does feel that the PM has resulted in thinner wheat in some fields due to secondary tiller death/sloughing, which PM can do.  He also indicated as did Dr. Brett Carver (OSU Wheat Breeder) that wheat at the Chickasha Station (about 50 miles southwest of OKC – central OK) is showing severe levels of leaf rust and (especially) stripe rust (Figure 1).  In more northwestern/north-central OK, only light levels of stripe and leaf rust were observed at the Lahoma Station, and Greg Highfill indicated that the variety trial near Alva, OK was “clean.”  He did indicated that west of Alva he had received reports of light levels of stripe rust.

 

The other disease that is definitely making a presence this year is wheat streak mosaic (WSM).  So far the lab has received 16 samples that have tested positive for Wheat streak mosaic virus (Figure 2).  These samples have primarily come from central and west-central Oklahoma, and typically have been associated with lack of controlling volunteer wheat in the field itself or in an adjacent field. Controlling volunteer wheat prior to the emergence of seedling wheat in the fall is critical to limiting WSM.  Once infection occurs, especially if it is a fall infection, wheat likely will be damaged in the spring (Table 1).  For more information on mite-transmitted wheat viruses such as WSM, please see OSU Fact Sheet EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) available at http://wheat.okstate.edu/wheat-management/insectsdisease/EPP-7328.

 

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Figure 1. Stripe rust and leaf rust on wheat in experimental trials at the Experiment Station at Chickasha, OK (photo courtesy of Dr. Brett Carver).

 

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Figure 2.  A commercial field of wheat showing severe WSM symptoms (A), a close-up view of WSM on an individual leaf (B), and a photo of the field immediately adjacent to the commercial wheat field in which abundant volunteer wheat had not been controlled until spring (C).

 

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Table 1.  Effect of time of infection by Wheat streak mosaic virus on the severity of wheat streak mosaic (WSM) and yield of three wheat varieties.  [Taken from Hunger, et al. 1992. Effect of planting date and inoculation date on severity of wheat streak mosaic in hard red winter wheat cultivars. Plant Disease 76:1056-1060.]

 

Reports/excerpts of reports from other states:

Dr. Erick DeWolf, Extension Plant Pathologist, Kansas State University, April 4, 2017:  “The Kansas wheat crop is currently at the boot and heading stages of development in the Southeast corner of the state. The Central and Western regions of the state are between jointing and flag leaf emergence.

Stripe rust was found in more fields this week with multiple reports in Southeast and South Central regions of the state. Most reports have come from the southern tier of counties bordering Oklahoma (see that attached map).  The disease was present in a lower and middle canopy; however, a few fields had infections of stripe rust on the leaf just below the flag leaf (F-1).  The disease was found primarily on the cultivar “Everest” which is known to be susceptible to stripe rust in previous years.  Weather conditions the past two weeks was very conducive for further spread of stripe rust with cool temperatures and frequent rainfall.  Therefore, additional finds of the disease are very likely.  The severity of the disease and risk of yield loss will be influenced by weather conditions over the next month.  Continued cool, wet weather will increase the risk of a severe problem with stripe rust in Kansas.  However, multiple days with high temperatures above 80 F, particularly with night time temperatures above 60 F, could slow the development of the disease.

 

Leaf rust was also reported this week south central Kansas.  The disease was at low levels but it is significant to leaf rust prior to heading in this region of the state.  Many popular varieties are susceptible to leaf rust including WB4458, T158, TAM111, TAM112, and Winterhawk. Growers should not overlook the potential threat of leaf rust in their fields.”

Wheat Disease Update – April 5, 2017

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

Yesterday (04-April) wheat in my foliar fungicide trial at the Plant Pathology Farm located just west of Stillwater appeared to be at GS 10 to 10.1 (head in the boot to awns just emerging from the boot).  The field was too wet to go out into, which seems to be the situation around much of the state (with more rain coming today and tonight).  Leaf rust can be found, but I have not seen any stripe rust.  Powdery mildew is heavy on lower leaves and spreading to mid-level leaves in wheat that has a heavy canopy.  Dr. Misha Manuchehri (Ast Prof & Weed Scientist, OSU) reported finding some heavier leaf rust in her experimental plots at Perkins, OK (about 15 miles south of Stillwater), but no or little leaf rust in surrounding trials/fields (Figure 1A).  Heath Sanders (Area Extn Agron Speclst, SW District) indicated to me on 04-Apr that wheat varied from boot to heads emerging across SW Oklahoma depending on planting date and management (primarily grazed or not grazed).  He has seen some leaf rust on lower leaves, but what has caught his attention more is the level of powdery mildew on lower and mid-level leaves in some wheat fields (early planted and not grazed).  This powdery mildew observation fits with what I have seen and with a photo received by Josh Bushong (Area Extn Agron Speclst, NW District) (Figure 1B).  Dr. Stephen Marek and his student Salome Suarez took a trip last Thursday to SW OK on a tan spot scouting trip and found plenty of tan spot in no-till fields.  He also found light leaf rust in some fields (Figure 1C), but again, no stripe rust.  Aaron Henson (Extn Educator, Tillman County, Southcentral OK) indicated quite a bit of the wheat in his area is headed and that he had seen some light leaf rust before the recent rains, but no stripe rust.

fig1afig1bfig1c

Figure 1. (A) Leaf rust pustules found on wheat in experimental trials near Stillwater, OK; (B) Severe powdery mildew as observed on lower and mid-level leaves in wheat in Custer County; (C) Scattered leaf rust pustules on a wheat leaf in southwestern Oklahoma.

 

The take-home message from these reports is that with the recent and forecast rain, foliar diseases (especially leaf rust and powdery mildew) likely will be increasing over the next couple of weeks.  Be prepared to apply a fungicide if necessary to protect a high yielding field, especially if that field is not highly resistant to leaf rust (and perhaps at least moderately resistant to powdery mildew).  More information about foliar fungicide use in Oklahoma wheat production can be found in the current report CR-7668 and is available at http://wheat.okstate.edu/wheat-management/insectsdisease/CR-7668web2017.pdf. Although a few citings have been made, it does not appear that stripe rust will be much of a disease factor this year.  Josh Bushong observed some active stripe rust in central OK near Hennessey (Kingfisher County; Fig 2A), and Dr. Manucherhi found some stripe rust in southwest OK near Altus (Jackson County) in the “telial” stage (Figure 2B).  The telial stage indicates that warm/hot temperature has caused the stripe rust fungus to go from the active state (Figure 2A) to a more dormant state (Figure 2B).

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Figure 2. (A) Stripe rust active pustules found on wheat near Hennessey in central OK; (B) Stripe rust “dormant” pustules (telia) found in southwest OK.

 

I also should reiterate that the Plant Disease and Insect Diagnostic Lab has received quite a few wheat samples over the past two weeks that have tested positive for either wheat streak mosaic (WSM) and/or barley yellow dwarf.  The number of positive samples for WSM especially has seemed somewhat high for this early in the spring.  In talking to producers or educators that submitted these samples it seems as though they typically are associated with volunteer wheat not being controlled in the field, or in a neighboring field.  For more information on mite-transmitted wheat viruses such as WSM, please see OSU Fact Sheet EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) available at http://wheat.okstate.edu/wheat-management/insectsdisease/EPP-7328%20three%20virus%20diseases%20of%20wheat.pdf.

 

Reports/excerpts of reports from other states:

Dr. Erick DeWolf, Extension Plant Pathologist, Kansas State University, April 4, 2017:  “Stripe rust was reported in Southeast Kansas today (April 4th). This is the first report of stripe rust in Kansas for the 2017 growing season.  The find was made by Josh Coltrain, KSU Agronomy Agent in the Wildcat Extension District.  The stripe rust was found in Montgomery county that borders OK in the Southeast corner of the state.  The wheat variety was “Everest” which is known to be susceptible to stripe rust.  The crop was planted in September (early for this part of the state) and is now at the heading stages for growth.  The weather conditions have been highly conducive for the disease in recent weeks and wheat growers in the state should intensify their scouting efforts. As of late-March, reports of pests and diseases included active brown wheat mites in many fields in Oklahoma as well as in some fields in southwest Kansas, symptoms of wheat streak mosaic in some counties in west central Kansas, barley yellow dwarf virus in central and south central Kansas, and tan spot in some fields in south central Kansas.”

 

Dr. Kirk Broders, Plant Pathologist, Department of Bioagricultural Sciences & Pest Management, Colorado State University, April 1, 2017:  “This years first wheat disease newsletter is coming a later than last year for several reasons, but the primary one is wheat disease in Colorado have been sparse. I was able to visit several wheat fields in Colorado along I-70 as well as along Hwy 34 on March 29 and 31. The rains have provided much needed moisture to the crop and overall the wheat is looking good. However, with the rain and moisture also comes the increased likelihood of foliar diseases caused by fungi such as stripe rust, powdery mildew and tan spot. In regards to stripe rust, there is no evidence the fungus survived the winter in Colorado and there have been few reports from south of us. So far this season, there has been sporadic reports of stripe rust from Texas, Louisiana, Mississippi and most recently from Oklahoma and further east in North Carolina and Virginia. However, there does not seem to be significant levels of pathogen inoculum, which bodes well for us in Colorado as it should require more time for the pathogen to reach Colorado. That being said with cooler temperature and more moisture in the forecast for much of the Central Plains next week, these conditions could give stripe rust the jump start it needs. I will continue to keep you posted on the progress of stripe and leaf rust in the central plains. The other foliar fungal diseases commonly survive in wheat residue and crops planted into a previous wheat crop are at a greater risk for disease development if the weather stays wet and overcast. Given all these considerations, I do not recommend an early season fungicide application as there is simply very low fungal pathogen pressure. The only exception might be wheat planted into wheat. I recommend these fields be scouted over the next couple weeks, to see if any disease develops after these rain events.

 

The diseases I did notice sporadically throughout the eastern Colorado, were viral diseases. I found both Wheat Streak Mosaic Virus (WSMV) and Barley Yellow Dwarf Virus (BYDV) in several fields. The incidence was lower than what has been reported in central and southwestern Kansas, where the disease seems to be particularly widespread. We may start seeing more symptoms of virus infection as the wheat breaks dormancy and starts growing more quickly. Many of these viral infection likely occurred last fall after the wheat germinated, and then we continued to have very mild temperatures until late November. This allowed the insects that vector both of these viruses to be more active in the fall for a longer period of time resulting in a greater number of infections in some areas. Once wheat is infected with either WSMV or BYDV there is no chemical treatment that can eliminate the pathogen. In fields where virus diseases are present it will be important to ensure volunteer wheat and weeds are managed, as these represent “green bridges” for the wheat curl mite, which vectors WSMV, to survive from one wheat crop to the next.”

2017 OSU Wheat Field Day Schedule Now Available!

The schedule, listed below, is also available on the home page of the wheat.okstate.edu website or by clicking here. We have 34 different stops lined up to talk about a lot of good wheat varieties available to producers. As the weather can force us to change plans at the last minute, please contact your local county Extension office with any questions on the date, time, and location.

2017 OSU wheat field days_final

Wheat Disease Update – March 25, 2017

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

 

Foliar wheat diseases remain relatively quiet in Oklahoma.  On scouting done around Stillwater and from trips taken Thursday and Friday to west and a bit northwest of Oklahoma City and northwest up to Enid, the only foliar diseases of any consequence observed were leaf spot diseases (e.g. tan spot) in no-till fields (Figure 1A).  Most of the wheat I saw was between 2 nodes readily apparent (GS 7) but ranged up to GS 8-9 (flag leaf just emerging to fully emerged).  In some fields, powdery mildew was moderately severe on lower leaves in “hot spots,” but again, not at a high frequency.  I saw no stripe and only sparse leaf rust, but Dr. David Marburger had a photo of stripe rust (Figure 1B) sent to him from a grower (Anderson Farms) that indicated the photo was taken from experimental plots at the Noble Foundation near Ardmore (Carter County).  Apparently there was not much stripe rust, but there were low to moderate levels of leaf rust (Figure 1C).

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Figure 1. (A) Tan spot symptoms as seen on wheat foliage in no-till fields; (B) stripe rust as seen in south central OK (Carter County); (C) a photo of leaf rust to compare with stripe rust.

Final first hollow stem update for the season – Goodwell 3/21/17

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8” or the diameter of dime) of stem below the developing grain head (full explanation). Last Friday (3/17), 6 of the remaining 8 wheat varieties reached FHS (Table 1). Joe and Spirit Rider were the final two, and both hit FHS yesterday (3/20). Keep in mind that several factors influence the onset of FHS. These include the wheat variety, location, temperature, available moisture, grazing, and planting date (later sown wheat will typically reach FHS later). The First Hollow Stem Advisor and the updates we provide give an indication of the FHS stem conditions in a particular area. However, because of the number of factors that can influence when FHS occurs, we cannot stress enough the importance of checking for FHS on a field-by-field basis. 

 

Table 1. First hollow stem (FHS) results by variety collected from non-grazed, irrigated plots at Goodwell on 3/9/17, 3/11/17, 3/13/17, 3/15/17, 3/17/17, and 3/20/17. Plots were sown on 10/6/16. The threshold target for FHS is 1.5 cm (5/8” or the diameter of a dime). The amount of hollow stem for each variety represents the average of ten measurements. Varieties that have reached FHS are highlighted in red.

table 1 goodwell 3.21.17

Assessing freeze injury on wheat

Temperatures in Oklahoma over the weekend (Fig. 1) and on Tuesday night into Wednesday morning (Fig. 2) dipped low enough to potentially cause some level of injury to the wheat crop. There were a number of areas that spent at least a couple hours with temperatures in the mid to lower 20s.

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Figure 1. Hours spent below freezing (32°F) last week (3/6 – 3/12). Most of these cold temperatures occurred from 3/11-3/12.

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Figure 2. Minimum air temperatures during Tuesday night (3/14) into Wednesday morning (3/15).

 

Keep in mind that the temperature recorded by the nearest weather station or at your house may not quite reflect the actual temperature that the wheat canopy experienced. Factors such as elevation and topography can influence the temperature, as well as things like large amounts of residue in a no-till situation, for example. Therefore, it is important to monitor each field.

 

What temperatures can damage wheat plants? This will depend on the growth stage. The susceptibility and temperature threshold to freeze injury steadily increases as we progress throughout the spring from jointing to heading and flowering. Earlier maturing varieties may be injured more from these recent freeze events than later maturing varieties because they are likely more advanced. Anecdotal evidence suggests there are varietal differences in resistance to spring freeze injury, but this is likely due to differences in plant growth stages when the freeze event occurred. Figure 3 provides a general guide, or rule of thumb, to the minimum temperature threshold and its impact on yield. It is difficult to have exact numbers because each freeze event is unique. While a field at the jointing growth stage could have spent two hours at 24° F, it is possible that the same amount of injury could occur with a 28° F temperature that was sustained for a longer period of time.

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Figure 3. Temperatures that can cause injury to winter wheat at different growth stages. Source: Kansas State University.

 

Another important thing to keep in mind is that we need to be patient before going out to assess freeze injury. The extent of a significant freeze event may not be apparent 1 or 2 days after. If warm temperatures return quickly, you should still wait about 5-7 days after the freeze event before determining the injury. If temperatures remain cool, it may take 10-14 days before the extent of the injury can be fully assessed. With our recent cold temperatures occurring earlier this week, beginning to check plants this weekend and into early next week should suffice, especially with the warmer temperatures forecasted.

 

What are some freeze injury symptoms to look for? With these recent freeze events, the most likely symptom will be leaf tip “burning” or “die-back” (Fig. 4). This is very often just cosmetic and will not hurt yield in the end. In areas that dipped into the lower 20s, damage can result in the entire leaf turning yellow to white, and the plants becoming flaccid (Fig. 5). You may even notice a “silage” smell after several days.

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Figure 4. Leaf tips which have turned brown (necrotic) due to freezing temperatures. Photo courtesy of Josh Bushong, OSU northwest area Extension agronomist.

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Figure 5. More severe freeze damage causing the leaves to turn yellow-white with plants losing their overall turgidity. Source: Kansas State University.

 

The most important plant part to check though is the growing point. To get a look at the growing point, you can slice the stem open lengthways. A healthy growing point will have a crisp, whitish-green appearance and will be turgid (Fig. 6). Often, you can lightly flick the head. If it does not break and bounces back, it is still healthy. If it is mushy, limp, and parts of it break off when you lightly flick it, then it has been compromised and will likely soon turn necrotic. Sometimes plants can appear healthy overall, but the growing point has been damaged or killed (Fig. 7-8). Another indication that the growing point has been compromised is the next emerging leaf is already necrotic.

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Figure 6. Close up of a healthy wheat head (growing point). Photo: Brenda Kennedy and Dr. Carrie Knott, University of Kentucky.

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Figure 7. Plants that appear healthy could have damaged heads. Photo: Dr. Jeff Edwards.

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Figure 8. A close up view of the damaged wheat head from Figure 7.

 

The last comment I want to make is the percent of damaged heads that you find may not translate into percent yield loss, especially with the growth stage a lot of our wheat is at. There is still opportunity for wheat even at the jointing stage (GS 6) to produce additional tillers and/or retain secondary tillers. Whether or not these tillers are able to compensate for larger tillers that were lost due to freeze will highly depend on the subsequent weather. If conditions are favorable, there is a chance for late emerging tillers to have a shot at producing grain. If the wheat is more advanced though, it will be tougher to make this type of recovery.

 

First Hollow Stem Update – Goodwell 3/16/17

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8” or the diameter of dime) of stem below the developing grain head (full explanation). Since our last post on Tuesday, 8 of the 16 wheat varieties measured yesterday by Dr. Tracy Beedy and her crew have reached FHS (Table 1). Keep in mind that several factors influence the onset of FHS. These include the wheat variety, location, temperature, available moisture, grazing, and planting date (later sown wheat will typically reach FHS later). The First Hollow Stem Advisor and the updates we provide give an indication of the FHS stem conditions in a particular area. However, because of the number of factors that can influence when FHS occurs, we cannot stress enough the importance of checking for FHS on a field-by-field basis. 

 

Table 1. First hollow stem (FHS) results by variety collected from non-grazed, irrigated plots at Goodwell on 3/9/17, 3/11/17, 3/13/17, and 3/15/17. Plots were sown on 10/6/16. The threshold target for FHS is 1.5 cm (5/8” or the diameter of a dime). The amount of hollow stem for each variety represents the average of ten measurements. Varieties that have reached FHS are highlighted in red.

table 1 3.16 goodwell

Wheat Disease Update – March 15, 2017

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

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

        I have not sent out an update since February 21 for several reasons, but the primary one is that wheat diseases in Oklahoma have been sparse. Wheat around Stillwater (STW) is at growth stage 6 or 7 and is showing good growth. On March 9, I looked at wheat in a loop from STW west to Marshall (30 miles west of STW) and Hennessy (50 miles west of STW), then south to Kingfisher and finally to El Reno (25 miles west of OKC). At that time and in the 8-10 fields/variety trials I stopped at, the only disease I saw was powdery mildew at a low incidence. On March 15, Patrick Rydzack (PLP graduate student), Branden Watson (Plant & Soil Science graduate student), and I visited trials at Chickasha (30 miles southwest of OKC), Apache (35 miles southwest of Chickasha), and again in El Reno. We found a few small pustules of leaf rust at Chickasha and some light to moderate powdery mildew (especially at Apache), but overall the foliage was green. Wheat at Apache was GS 7 (2 nodes at base of stem). These observations and other input from around the state indicate that leaf rust is present only in trace amounts, and stripe rust has yet to be observed in Oklahoma.

        In contrast, I have seen tan spot and have heard several reports of leaf spot diseases in no-till fields. On March 13, Josh Bushong (NW Area Extn Agron Speclt), Corbin DeWitt (Extn Edctr-Kay County), and I visited a field near Ponca City that had severe tan spot on the lower leaves; in my estimation, sufficiently severe to merit a fungicide application. I also have had similar situations described to me from fields in Kiowa County (southwest OK), but have not directly seen them. Typically tan spot/Septoria/Stagonospora (the leaf spot foliar diseases) are more severe in no-till fields where wheat residue has been retained on the soil surface. The leaf spots on lower leaves (Figure 1) can be severe and will continue to move up the foliage as long as moisture and temperature are favorable.

fig1a

fig1b

Figure 1. (top picture) Severe tan spot on lower wheat leaves. Note wheat residue on soil surface in the background.  (bottom picture) A close up of wheat residue with ‘pseudothecia’ (i.e., spore containing structures) of the fungus that causes tan spot.  Spores are released from these structures that infect the lower wheat leaves.

        If infection is severe on lower leaves, spraying with a fungicide (this early in the season I would go with the lesser expensive generic fungicide) will help limit spread of these leaf spot diseases to older foliage. For additional information regarding early season foliar wheat diseases and possible control with an early fungicide application, see our fact sheet (PSS-2138) that discusses split application of fungicides by clicking here or visiting the wheat.okstate.edu website.

Reports/excerpts of reports from other statesI received a report of leaf rust in south Texas from Dr. Gary Odvody (Texas A&M AgriLife Research & Extension Center, Corpus Christi, TX). However, this report indicated only that leaf rust was observed and mostly focused on severe oat crown rust, which will not infect wheat.