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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Wheat Disease Update – 6 April 2018

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

 

Powdery mildew (Figure 1) is showing up on lower leaves in fields and trials around Stillwater, and I have also had reports of powdery mildew on lower leaves from Extension Educators around the state. I also have seen ‘hot spots’ indicative of barley yellow dwarf (Figure 2) around Stillwater, but did not find any aphids associated with these spots. From Texas, Dr. Clark Neely(Small Grains and Oilseed Extension Specialist; Texas A&M AgriLife Extension) relayed to me on April 4 that, “Overall, I think we have avoided the stripe rust and what little was around is shutting down now. Leaf rust is around, but seems lighter than normal for the moment.” Across Oklahoma, wheat leaf and stripe rust still are largely absent, although a few “stripes” of stripe rust were found by Zack Meyer here at Stillwater this morning at an Extension Educators in-service training. This lack of the rusts in Oklahoma is supported by the recently implemented scouting program involving Oklahoma Extension Educators. This program asks county educators to look for and report weekly the occurrence of stripe rust, leaf rust, and/or powdery mildew they observe in commercial fields, variety trials, or variety demonstrations located in their counties. This information is reported by county educators from counties across southern Oklahoma to Heath Sanders (Area Extension Agronomy Specialist; southwest district), from counties across mid-Oklahoma to Zack Meyer (Extension Educator; Kingfisher County) and from counties across northern Oklahoma to Josh Bushong (Area Extension Agronomy Specialist; northwest district). The incidence and severity of these three wheat foliar diseases can then be more accurately summarized and disseminated to facilitate decisions related to applying a fungicide to help manage these diseases on susceptible varieties. For the week ending on April 5, observations reported from across southern and mid-Oklahoma (Jackson, Dewey, Washita, Blaine, and Kingfisher Counties) indicated no leaf or stripe rust and only one report of powdery mildew on lower and mid-leaves in Washita County. It is still a bit early for reports to come in from across northern Oklahoma. Thanks are extended to all the educators that participated in this pilot program, and I would encourage more participation to facilitate this reporting program.

 

Figure 1.  Powdery mildew observed April 5 on lower leaves of wheat in trials around Stillwater, OK.

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Figure 2.  Likely barley yellow dwarf (BYD) “hot spot” observed on wheat in early April (top photo). As time proceeds, these hot spots will develop stronger symptoms of BYD including leaf discoloration ranging from yellowing (middle photo) to purpling in some varieties (bottom photo).

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2018 OSU Wheat Field Day Schedule Announced

We have 32 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. The schedule listed below is also available on the home page of the wheat.okstate.edu website or by clicking here.

 

A special thanks goes out to the area and county Extension personnel and grower cooperators on helping get these field days scheduled!

2018 OSU wheat field days

 

Impact of recent cold temperatures on Oklahoma wheat

Temperatures on Easter into Monday (Figure 1) and last night into this morning (Figure 2) dipped low enough throughout a large portion of the state to potentially cause some level of injury to the wheat crop. There were a number of areas that spent a significant amount of time with temperatures in the mid to lower 20s over the course of these two cold snaps. Areas in the northwest and into the Panhandle even got as cold as the mid to upper teens. On top of all that, we have cold temperatures forecasted again for later this week.

 

Figure 1. Minimum air temperatures (top graph) during Easter into Monday (April 1-2) and hours spent below freezing (32°F) over the past 48 hours during that same time frame (bottom graph).

April2minairtemp

April2cumulative.freeze.48hr

 

Figure 2. Minimum air temperatures (top graph) during last night into this morning (April 3-4) and hours spent below freezing (32°F) over the past 48 hours (bottom graph).

April4today.TAIR.min.grad

April4cumulative.freeze.48hr

 

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, especially as you increase the distance from where the temperature was recorded and the field itself. 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.

 

What are the temperatures that can damage the wheat plants?

This will depend on the growth stage of the plants. 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. Earlier maturing varieties are more likely to be injured from these recent freeze events than later maturing varieties because they are likely more advanced. The susceptibility of the wheat plants to freeze injury does steadily increase as we progress throughout the spring from jointing to heading and flowering. Figure 3 listed below is a general guide to the minimum temperature threshold and its impact on yield. These numbers are not exact but provide a decent rule of thumb. It is difficult to have exact numbers because each freeze event is unique. While a field at the jointing growth could spend two hours at 24 F, it is possible that the same amount of injury could occur with at 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 publication C646: Spring Freeze Injury to Kansas Wheat.

 

How long should I wait to assess injury?

Another important thing to keep in mind is that we need to be patient before going out an assessing 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 wait about 5-7 days before determining the injury. If temperatures remain cool after the freeze event, it may take 10-14 days before the extent of the injury can be fully assessed. Since we still have cooler temperatures in the forecast, we will likely need to wait closer to the 10-14 days.

 

What are some freeze injury symptoms to look for?

A common freeze injury symptom is leaf tips turning yellow and necrotic (Figure 4). This is very often just cosmetic and will not hurt yield in the end. More severe damage can result in the entire leaf turning yellow to white and the plants become flaccid (Figure 5). You may even notice a “silage” smell after several days.

 

Figure 4. Leaf tips which have turned necrotic due to freezing temperatures. Photo taken in March 2017 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 publication C646: Spring Freeze Injury to Kansas Wheat.

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The most important plant part to check is the growing point. This will be important for areas of the state that have fields with plants which are at jointing or past jointing. Sometimes we can see what look like healthy plants overall, but the growing point has been damaged or killed. 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 be turgid (Figure 6). Often, you can lightly flick the head, and if it bounces back and does not break, it is still healthy. If it is mushy, limp, and breaks or parts of it break off when you lightly flick it, it has been compromised. It may also have a brown color (Figure 7). Another indication that the growing point has been compromised is the next emerging leaf is necrotic.

 

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

 

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Figure 7. Plants that appear healthy could have damaged heads. Photo taken several years ago courtesy of Dr. Jeff Edwards.

 

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Figure 8. A close up view of the damaged wheat head from Figure 7. Photo taken several years ago.

 

Also, the percent of damaged heads may not translate into percent yield loss. There is still opportunity for wheat 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 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, it will be tougher to make this type of recovery.

 

Do drought conditions exacerbate freeze injury?

When it comes to this question, it is really a mixed bag of results. A lot of anecdotal evidence suggests drought conditions can make freeze injury worse, and that could very well be the case in some scenarios. Water in the soil is a good buffer to resist temperature swings and can prevent the soil from cooling as quickly as the air around it. Therefore, the temperature at the soil surface of a conventionally tilled field with good soil moisture may not get as cold as a similar field with dry soil conditions for example.

 

In theory, the plants themselves under drought conditions should actually be able to withstand cooler temperatures than non-stressed plants as less water content in the plant cells increases the solute concentration (i.e., it takes longer for those cells to freeze). Using the conventionally tilled field example above, we cannot automatically say that a field with dry soil conditions will have worse freeze injury than a field with adequate moisture. Also, if the weather conditions during the day(s) prior to the freeze event were warm and sunny, a significant amount of heat may still be radiated from a field with dry soil conditions and provide some buffer against freeze injury.

 

Final thoughts

Remember that each freeze event is unique. The amount of injury observed will depend on the growth stage of the plants, how low the temperature got, and how long it stayed at those cold temperatures. Other factors such as elevation, residue cover, and moisture can influence the observed temperature within the canopy as well. Because of the number of influential factors, it is important to check each field. It is possible to have variability in injury symptoms among fields and even within fields.

 

Wheat Disease Update – 29 March 2018

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 am still not seeing any foliar diseases around Stillwater, but reports are indicating that inoculum of the wheat rusts (stripe and leaf) have started to increase in Texas. On March 21, Dr. Clark Neely (Small Grains/Oilseed Extension Specialist; Texas A&M AgriLife Extension) indicated that, “A report from Uvalde, TX late last week indicated stripe rust had increased significantly on susceptible checks. A fungicide trial in College Station, TX showed stripe rust building in the lower canopy. Flag leaves were still pretty clean, but F1 and F2 leaves were 5% or greater in much of the trial. The field surrounding the trial did not show any obvious signs of stripe rust at this time, but showed heavier levels of leaf rust. Talked to a grower in the Waco area and he reported leaf rust building in his wheat fields as well.  Expecting dry conditions through the weekend but then turning wet for much of next week, which could facilitate further development.

 

Dr. Amir Ibrahim (Professor & Small Grains Breeder/Geneticist; Texas A&M AgriLife Research) indicated a somewhat similar scenario for wheat rust in south and central Texas by stating on 23-March that, “Uvalde seems to be the first location where we detect wheat stripe rust every year.  Stripe rust is also active at Castroville, College Station and McGregor. Warming temperatures expected at these locations may slow it significantly during coming weeks.”  Based on these two reports and the recent weather conditions in Oklahoma, I would expect stripe and leaf rust to begin to appear across Oklahoma where moisture was received over the last week. It likely has been too dry in western/northwestern OK and the panhandle to facilitate wheat rusts.  Powdery mildew may begin to occur because powdery mildew does not require free moisture but rather just high humidity (see next paragraph).

 

Lanie Hale (Wheeler Brothers located in Geary, OK) indicated on March 29 that, “I’ve been in lots of fields this week; Canton, Okeene, Loyal, Geary, Greenfield and Calumet areas. The dry weather is taking its toll now and reducing harvested bushels daily in most fields I’ve been in. I’m seeing winter grain mites and brown wheat mites, with a few green bugs and cherry aphids. In some of these fields, the mites are taking additional yield also. Mites are a dry weather pest, if we could get a good rain the wheat would outgrow them, but if it doesn’t rain, there’s not going to be much of crop even if sprayed. Heavily grazed fields are failing, but the late planted, well fertilized, ungrazed fields are holding on fairly well (Figure 1). Brian and I saw lots of powdery mildew (Figure 2). This was a field with a thin stand, open canopy, top of the hill, red ground.”

 

Figure 1.  Grazed field (to the right) compared to a non-grazed field (to the left) in western/west-central Oklahoma on about 28-March-2018. (Credit:  Lanie Hale, Wheeler Brothers).

grazedvsnotgrazed

 

Figure 2.  Severe powdery mildew infection observe in central/west-central Oklahoma on the lowest leaves in a wheat canopy. Note how leaves above these lowest leaves appear to not be so heavily infected. Photo credit to Lanie Hale, Wheeler Brothers.

powdery mildew

Final First Hollow Stem Update – 3/22

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). To give you a point of reference, the average FHS date over the past 20 years at Stillwater is March 6.

 

The latest FHS results from Chickasha (Table 1) and Stillwater (Table 2) are listed below. All wheat varieties at Chickasha and Stillwater have now reached the 1.5 cm threshold, and some of the remaining varieties flew past the threshold since the last sampling date.

 

Keep in mind that several factors influence the onset of FHS. These include the wheat variety, location, temperature, available moisture, level of 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 wheat, triticale, rye, barley, and oat variety collected on 2/20/18, 2/26/18, 3/2/18, 3/6/18, 3/8/18, 3/12/18, 3/15/18, and 3/20/18 at Chickasha. Plots were sown on 9/25/17. 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 from non-grazed plots. Varieties that have reached FHS are highlighted in red.

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Table 2. First hollow stem (FHS) results by wheat variety collected on 2/27/18, 3/5/18, 3/8/18, 3/13/18, 3/16/18, and 3/21/18 at Stillwater. Plots were dusted in on 9/15/18 and did not receive significant rainfall until 9/25/17. The triticale, rye, barley, and oat plots were abandoned due to emergence issues. 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 from non-grazed plots. Varieties that have reached FHS are highlighted in red.

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First Hollow Stem Update – 3/16

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). To give you a point of reference, the average FHS date over the past 20 years at Stillwater is March 6.

 

The latest FHS results from Chickasha (Table 1) and Stillwater (Table 2) are listed below. All but two of the wheat varieties at Chickasha are at FHS, but the two holdouts are very close. At Stillwater, 10 of the 18 remaining wheat varieties reached FHS today. A majority of the 8 varieties left will likely reach FHS soon.

 

Keep in mind that several factors influence the onset of FHS. These include the wheat variety, location, temperature, available moisture, level of 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 wheat, triticale, rye, barley, and oat variety collected on 2/20/18, 2/26/18, 3/2/18, 3/6/18, 3/8/18, 3/12/18, and 3/15/18 at Chickasha. Plots were sown on 9/25/17. 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 from non-grazed plots. Varieties that have reached FHS are highlighted in red.

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Table 2. First hollow stem (FHS) results by wheat variety collected on 2/27/18, 3/5/18, 3/8/18, 3/13/18, and 3/16/18 at Stillwater. Plots were dusted in on 9/15/18 and did not receive significant rainfall until 9/25/17. The triticale, rye, barley, and oat plots were abandoned due to emergence issues. 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 from non-grazed plots. Varieties that have reached FHS are highlighted in red.

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Wheat Disease Update – 14 March 2018

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 spent Monday (March 12) looking at wheat around Stillwater and found no foliar diseases. Gary Strickland (Extension Educator; Jackson County) indicated the same for southwestern OK. He indicated wheat is short and drought stressed with flag leaves emerging in some wheat even though it is only about 4 inches tall. Josh Bushong (Area Extn Agronomy Specialist) indicated a similar scenario for wheat west of Lahoma, (10 miles west of Enid). He also indicated he had heard of some spraying being done for aphids – both for bird cherry–oat and greenbug.

 

At this point, it appears there is not much rust inoculum building up to the south of us in Texas. On March 9th, Dr. Clark Neely (Small Grains/Oilseed Extension Specialist; Texas A&M AgriLife Extension) scouted sentinel plots for foliar diseases. Here is his report. “I checked sentinel plots at College Station, TX on Friday, March 9, for disease. I found moderate levels of stripe rust in ‘Sisson’ only. I did not observe stripe rust in any other sentinel plots. I was unable to go through the entire variety trial at the time, but there were no obvious signs of a stripe rust epidemic. There were trace amounts of stripe rust found in a nearby fungicide trial on ‘WB 4303’. There have been no reports from growers anywhere in the state yet of stripe rust in producer fields. Leaf rust was found on these varieties as well, but in trace amounts. Overall, leaf rust is much lower this time of year compared to the past two years due to cold temperatures we experienced this winter. Powdery mildew is very common due to cloudy, damp weather the past month and dense canopies. Many winter varieties are around Feekes 7-8. Hard red spring wheat ‘LCS Trigger’ in an adjacent trial was the most advanced of anything I observed and was at Feekes 9 (fully emerged flag leaf).” I have included one photo from Dr. Neely because it is an excellent photo that shows the difference between the pustules of an early infection of stripe rust and leaf rust (Figure 1).

stripe and leaf rust

Figure 1. Early stripe rust on wheat near College Station, TX observed on March 9 by Dr. Clark Neely (Small Grains/Oilseed Extn Specialist; Texas A&M AgriLife Extension). Compare the stripe rust pustules located on the left to the three leaf rust pustules on the right side of the leaf.

 

Finally, the OSU Diagnostic Lab has tested 11 samples from southwestern OK (Washita County) for the wheat viruses that cause wheat streak mosaic, high plains, Triticum mosaic (all transmitted by the wheat curl mite) and barley yellow dwarf (aphid transmitted). We are doing this to see if testing for the presence of these viruses early in the season with the ELISA procedure may have value in giving producers a “heads-up” related to the decision of removing cattle or to graze out a given field. We will follow these fields as the season progresses to see how the incidence of these viruses in these fields relates to the virus testing.

First Hollow Stem Update – 3/14

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). To give you a point of reference, the average FHS date over the past 20 years at Stillwater is March 6.

 

The latest FHS results from Chickasha (Table 1) and Stillwater (Table 2) are listed below. Most of the wheat varieties at Chickasha have reached FHS, and the three remaining varieties will likely meet the threshold very soon. The warm temperatures at Stillwater over the weekend helped move a number of varieties along quickly. During yesterday’s measurements, 20 more varieties (36%) reached the 1.5 cm threshold. There are still 18 varieties which have not reached FHS at this location.

 

Keep in mind that several factors influence the onset of FHS. These include the wheat variety, location, temperature, available moisture, level of 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 wheat, triticale, rye, barley, and oat variety collected on 2/20/18, 2/26/18, 3/2/18, 3/6/18, 3/8/18, and 3/12/18 at Chickasha. Plots were sown on 9/25/17. 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 from non-grazed plots. Varieties that have reached FHS are highlighted in red.

chick3.14

 

Table 2. First hollow stem (FHS) results by wheat variety collected on 2/27/18, 3/5/18, 3/8/18, and 3/13/18 at Stillwater. Plots were dusted in on 9/15/18 and did not receive significant rainfall until 9/25/17. The triticale, rye, barley, and oat plots were abandoned due to emergence issues. 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 from non-grazed plots. Varieties that have reached FHS are highlighted in red.

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First Hollow Stem Update – Week of 3/5-3/9

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). To give you a point of reference, the average FHS date over the past 20 years at Stillwater is March 6.

 

The latest FHS results from Chickasha (Table 1) and Stillwater (Table 2) are listed below. Wheat stem elongation overall at Chickasha is starting to progress quickly now. As of March 6, 21 of the 31 wheat varieties (68%) have reached the 1.5 cm threshold, with 14 of those 21 varieties reaching the threshold on March 6. Stem elongation at Stillwater is moving, but not at the same pace as Chickasha. As of yesterday, March 8, only 18 of 56 wheat varieties (32%) have reached the 1.5 cm threshold.

 

Keep in mind that several factors influence the onset of FHS. These include the wheat variety, location, temperature, available moisture, level of 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 wheat, triticale, rye, barley, and oat variety collected on 2/20/18, 2/26/18, 3/2/18, and 3/6/18 at Chickasha. Plots were sown on 9/25/17. 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 from non-grazed plots. Varieties that have reached FHS are highlighted in red.

chick3.9

 

Table 2. First hollow stem (FHS) results by wheat variety collected on 2/27/18, 3/5/18, and 3/8/18 at Stillwater. Plots were dusted in on 9/15/18 and did not receive significant rainfall until 9/25/17. The triticale, rye, barley, and oat plots were abandoned due to emergence issues. 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 from non-grazed plots. Varieties that have reached FHS are highlighted in red.

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What can I expect from wheat just now emerging?

Dusted-in wheat and spotty stands this past fall was a more common occurrence than we want to see in Oklahoma. Going into winter though, I thought we would get precipitation at some point to get the remaining seed to germinate, similar to the situation in northwestern Oklahoma last growing season. Unfortunately that did not happen, and the first water some of this seed has seen came with the late February rain. Now the remaining seed is germinating and emerging, begging the question what is a realistic expectation for this late-emerging wheat crop?

 

Will these plants produce a head?

In order to produce a head, winter wheat must be vernalized, which means it requires exposure to cool temperatures to trigger reproductive development. Winter wheat plants that do not go through vernalization will continue to grow vegetatively (i.e., produce leaves and tillers) but will not joint and produce a seed head (Figure 1).

 

How cold and for how long?

In the literature, you will often see that winter cereals require exposure to cooler temperatures (33° to 51° F) for six weeks. However, the exact temperature and time period differs by variety. A general rule of thumb is varieties that are more winterhardy and later maturing tend to require lower temperatures for a longer period of time (i.e., a stronger vernalization requirement) than less winterhardy and earlier maturing varieties. Vernalization requirements for winter wheat varieties adapted to the southern Great Plains may range from 120 to 1080 hours (5 to 43 days) below 45° F (Neely, 2016).

 

Since this is a rare problem in Oklahoma, we do not have much data on variety-specific vernalization requirements. I spoke with Dr. Carver, and he feels exposure to constant temperatures at or below 45° F for three weeks should be sufficient for most winter wheat varieties grown in Oklahoma. If that time decreases to two weeks, though, there is a possibility that we may run into vernalization issues for some varieties. It is important to keep in mind that the vernalization clock starts clicking once the seed imbibes water and sprouts. Some good news is we have been experiencing cooler temperatures since the rain, and cooler temperatures are still in the forecast.

 

Figure1

Figure 1. Example of a wheat variety which was able to vernalize (left foreground) versus a variety that was not able (right foreground). Notice these differences in varieties from the foreground to the background. This photo was taken by Bryan Simoneaux at a Texas winter wheat variety trial.

 

Is it all just temperature dependent?

In addition to vernalization, many varieties have a photoperiod signal that can tell the plant to switch to reproductive growth regardless of the temperature. Therefore, if we do not get enough time spent with cooler temperatures to satisfy vernalization, the plant will still initiate reproductive development once the daylength has become long enough. However, the plants in this scenario will likely be two weeks or more behind in development compared to normal.

 

Do we have information on varieties?

While we do not have variety-specific vernalization requirements at the moment, parts of south Texas will experience vernalization problems now and then. This happened at the Wharton variety trial location in 2016. Some varieties at this location were able to produce grain while others did not. Looking at these results may give us an indication which varieties grown in Oklahoma this year might have a higher probability of producing heads (Table 1).

Table 1

Table 1. The 2016 Wharton, TX wheat variety trial results in which mild winter conditions resulted in vernalization issues for some varieties. Varieties that were able to still produce grain are those ranked 1-16.

 

What forage or grain yield potential do I have?

To dive into this question, we do have some data from Kansas that can provide some guidance. Researchers at Kansas State University conducted a seven-year study (1985-1991) near Garden City, KS where they planted winter wheat every month from October 1 to April 1 (Witt, 1996). They used one variety (TAM 107) and a seeding rate of 80 lbs/acre for each planting date. Table 2 summarizes the data from this study.

 

Wheat planted on all dates through March 1 was able to produce grain each year. Wheat planted on April 1 did not joint and produce heads. Relative to the October 1 planting date, the wheat planted on March 1 was:

  • the lowest yielding;
  • was the shortest statured (5 in. less);
  • had the most delay in heading (26 days later);
  • had the shortest grain-filling period (9 days fewer).
  • was the last to ripen (17 days later);
  • produced the fewest heads per plant (58% fewer);
  • produced the fewest kernels per head (33% fewer) and the fewest kernels per plant (73% fewer);
  • and produced the smallest seed weight (43% less) and the lowest test weight (59% less).

Table2

Table 2. Wheat response to delayed planting dates near Garden City, KS from 1985-1991 (Witt, 1996).

 

While there was variability in grain yield among the years, the average relative grain yield for each planting date compared to the first planting date was: October 1 = 100%, November 1 = 77%, December 1 = 59%, January 1 = 57%, February 1 = 41%, March 1 = 16%, and April 1 = 0%.

 

Forage data was not collected in this KSU study, so it is hard to say that the percent decrease in forage yield would be similar to the grain results. We can make some educated guesses on what the forage potential might have been, though. The number of heads per plant in the March 1 planting date was 58% less than the October 1 planting date (i.e., 58% less tiller production), and plant height was 20% less for the same comparison. So, it may not be out of the question to say that there was probably a 50-75% reduction in forage yield. Unless your seeding rate was significantly increased to compensate for less tiller production, the bottom line is that there is a low probability that late-emerging wheat will generate much tonnage.

 

In Oklahoma, especially southern Oklahoma, we warm more quickly than the location for the KSU study. Their March 1 planting date is probably more like a February 15 planting date in Oklahoma. Again, this is all estimation, but when taking this and the Kansas data into consideration, the February emergence dates for some of our Oklahoma wheat puts us in vernalization limbo. Only time will tell us whether or not our wheat was exposed to enough cooler temperatures to trigger reproductive development. Again, the good news is we are still getting these cooler temperatures. If we do run into the scenario where we do not get enough cooler temperatures but still go through reproductive development because of the photoperiod component, our forage or grain yield will likely be even lower, as growth and development will be extremely delayed.

 

We’re working on it

To help us gather more variety specific information on whether heads and grain will be produced or not, we planted 36 different wheat varieties at Stillwater on March 6. I will post pictures and updates of this study to keep you informed as to what we are seeing and likely outcomes.

 

Final thoughts:

  1. If you have crop insurance, contact your agent to discuss your options.
  2. To get a ballpark estimate on what your forage or grain yield potential might be, you need to first assess your stand. Ideally, we need 60-70 heads per square foot to maximize grain yield potential. In areas that typically have lower yield potential, we can likely lower that number to 50-60 heads per square foot. To help you with your tiller counts and yield estimates, you can find more information in fact sheet PSS-2149: Estimating Wheat Grain Yield Potential.
  3. Wheat that was established prior to the February rain will have had enough time under cooler temperatures to vernalize and go through reproductive development. For most of these acres which did receive rain, we still have a chance at producing full or close full yield potential if the wheat tillered or if you increased your seeding rate to compensate for the late planting.
  4. For those who had spotty stands prior to the rain, we can still get an estimate on potential here too. You will need to estimate the percent of the field with an established stand, and then obtain a plant/tiller count as described above. Again, these established plants may still have full yield potential. For the plants now emerging, I doubt we will get much, if any, additional tillers produced. Also, the amount of grain produced by that single head will likely be less (refer to Table 2 for an estimate on how much less), unless the variety has a low vernalization requirement (Table1 may give indication to varieties with a lower vernalization requirement).
  5. With wheat that was planted very late and is just now emerging (after cotton in southwest Oklahoma for example), again, I doubt there will be additional tillers produced. The grain yield potential here may be similar to the results described in the Kansas study. If a producer increased their seeding rate to compensate for less tiller development, the amount of grain yield reduction may not be as much depending on the seeding rate, but it will still likely not reach close to full yield potential.

 

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