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Oklahoma Wheat Harvest Begins for the 2021 Season, Amid Cooler Temperatures and Heavy Moisture

Courtesy Oklahoma Wheat Commission

The 2021 wheat harvest has begun with several locations in Southwest, Oklahoma, reporting a successful weekend for grain being received.  The following counties that received grain in elevator locations were Harmon, Jackson, Tillman, Cotton, Comanche, Kiowa and Greer.  A few reports of sample loads being accepted in Frederick on Saturday, May 29th. Rain showers across Southwestern, Oklahoma, over the Memorial Day weekend hindered producers from making any progress over this past week until Saturday, June 5th.  During this period, cooler temperatures, cloud cover and high moisture levels on the grain have slowed progress on harvesting the crop.   Traditionally combines are rolling in Southwest, Oklahoma Memorial Day weekend or before, but unseasonable cool temperatures and rain has delayed the crop maturing.  High quality and favorable test weights have been noted so far.   Rains across Southwest, Oklahoma, late last night and early this morning have put harvest on standstill again in several regions, while in other areas producers hope to get rolling again later this afternoon, west of Tillman and Kiowa counties.  In a large area of Tillman county, producers are reporting 3 to 5 inch rains last night, which will delay harvest another 4 to 5 days.  Regions of Cotton and Comanche county locations received 1/10th to 2.5 inches of moisture depending on location.

Overall early wheat that has been harvested in Southwest, Oklahoma, indicates strong quality and decent yields. Yields reported varied depending on locations and producer management.  Test weights are averaging 60 lbs./bu. or higher.  While it is premature to report on protein, early numbers are ranging between 11 and 12 percent.

Grandfield/Devol- Harvest started over the weekend, although moisture last night will make it a late start today. More moisture was reported around Grandfield with less rain in the Devol area where combines will likely start up again.   Test weights for this region being reported at 60 +.  Yields around Grandfield and Devol have been favorable ranging from 40 to 50 bushels per acre.   One field has been reported at 70 bushels per acre.

Frederick/Chattanooga- The past two days have been successful for harvest in this region, but heavy rains last night across Tillman County is going to hinder harvest most likely another 4 to 5 days depending on the location.  Three to five inch rains from elevator managers in this region being reported today.  Areas of heavy rain did not report on Mesonet due to the nature of pop- up storms. Test weights ranging from 60 to 61 lbs./bu. Yields in this region not being reported as favorable as Comanche County but still ranging from the high 30’s on heavily grazed wheat to the mid 40’s on early cuttings.

Altus/Duke- Harvest was successful in this region over the weekend, while light moisture and humidity will most likely hinder harvest in Altus.  Little rain was received out at Duke so producers are hopeful combines in this area as well as in Harmon and Greer Counties will move later today. Note: much of the wheat in Harmon and Greer counties was cut for hay due to the excessive ongoing drought in this region.  Test weights in this area being reported at 61 to 62 lbs./bu.  Yields being reported from high 30’s to mid 60’s on fields with extremely progressive management systems.

Lone Wolf/Hobart-Producers also had success with harvesting in this region over the past two days.  Light rains and higher humidity will likely hinder an early start to harvest today in most places, certain regions may be delayed longer from getting into the fields in Kiowa county.  Test weights in this region averaging 62.4 lbs./bu. Yields being reported from the mid 30’s to mid 50’s depending on location and management.

Sentinel/Rocky- While it was close to starting this weekend at these locations, light rains today will most likely hinder harvest another couple days in this area.  No wheat was reported as taken in at these locations over the weekend.

Enclosed, see the 14-Day and 12-Hour rainfall accumulation maps with the 7-day weather forecast for Oklahoma.

The next harvest report by the Oklahoma Wheat Commission will be published Wednesday, June 9, 2021.

Lahoma Field Day is this Friday – May 14!

Are you planning to attend the in-person event?

Please pre-register here: http://wheat.okstate.edu/plot-tours/21EXT_Lahoma_eFlyer_altFINAL.pdf

The program will start a little earlier at around 8:45am and the presentations will start at 9:15am. 

Are you planning to watch it online? 

Please see below the livestream link for each presentation. All you need to do is to click on the link at the time of each talk.

9:15 am – Wheat Varieties – Amanda Silva, Small Grains Extension Specialist

10:00 am – Integrated Weed Management – Misha Manuchehri, Weed Science Extension Specialist

10:45 am – Wheat Breeding and Disease Update – Brett Carver, Wheat Breeder and Bob Hunger, Extension Wheat Pathologist

All of these will be available live at www.youtube.com/sunuptv

For more information go here: http://wheat.okstate.edu/plot-tours/21EXT_Lahoma_eFlyer_altFINAL.pdf

Looking forward to seeing you there!

First hollow stem nearing

First hollow stem occurs just prior to jointing and is the optimal time to remove cattle from wheat pasture. Given the warm forecast for the next two weeks, it is likely that we will start seeing first hollow stem in Oklahoma wheat fields. Grazing past first hollow stem can reduce wheat grain yield by as much as 5% per day and the added cattle gains are not enough to offset the value of the reduced wheat yield.

Similar to previous years, we will monitor occurrence of first hollow stem in our wheat plots at Stillwater and report the findings on this blog. There is also a first hollow stem advisor available on the Oklahoma Mesonet that can assist in determining when to start scouting.

Checking for first hollow stem is fairly easy.

  • You must check first hollow stem in a nongrazed area of the same variety and planting date. Variety can affect date of first hollow stem by as much as three weeks and planting date can affect it even more.
  • Dig or pull up a few plants and split the largest tiller longitudinally (lengthways) and measure the amount of hollow stem present below the developing grain head. You must dig plants because at this stage the developing grain head may still be below the soil surface.
  • If there is 1.5 cm of hollow stem present (see picture below), it is time to remove cattle. 1.5 cm is about the same as the diameter of a dime.
  • Detailed information on first hollow stem can be found at www.wheat.okstate.edu under ‘wheat management’ then ‘grazing’
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Is this the year for split fungicide application?

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

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

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

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

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

Wheat stripe rust

Wheat stripe rust

This overhead shot of the 2015 Chickasha intensive and standard wheat variety trials illustrates the severity of stripe rust in the region. The intensively managed trials on the left was treated with a fungicide just prior to heading. The standard trial on the right has the exact same varieties but no fungicide. The "middle" replication between the two studies is a border of Ruby Lee that is 1/2 treated 1/2 non treated.

This overhead shot of the 2015 Chickasha intensive and standard wheat variety trials illustrates the severity of stripe rust in the region. The intensively managed trials on the left was treated with a fungicide just prior to heading. The standard trial on the right has the exact same varieties but no fungicide. The “middle” replication between the two studies is a border of Ruby Lee that is 1/2 treated 1/2 non treated.

Q & A regarding PVP seed laws

Stories about seed law violations and fines have sprung up occasionally in the farm press over the past few years. These stories have tended to focus on the “penalty” part of the law and the magnitude of the fines rather than how the law protects Oklahoma farmers’ investments in wheat variety development and the provisions in the law that allow farmers to save seed for replanting. The purpose of this article is to answer some of the most frequently asked questions regarding the PVP law.

What is PVP?
The Plant Variety Protection Act (PVP or PVPA) is a federal seed law designed to protect the intellectual property of plant breeders, seed producers, and those who have funded variety development (in our case OSU and Oklahoma Taxpayers). The PVP law that you read about in the news today was enacted in 1994 and was an amendment to a law originally passed in 1970. The law prohibits the sale of farmer-saved seed without the variety owner’s permission. This protection lasts for 20 years for most crops. The ‘Title V’ you sometimes see tacked on to the end of PVP, refers to an amendment to the federal seed act stating that the variety can only be sold as a class of certified seed and by variety name.

Can I save seed from PVP-protected varieties?
Yes. You can save seed from PVP-protected varieties to plant on land you own or rent. You just cannot sell or trade the seed for planting purposes. A comparable example is an audio cd. You can make extra copies of an audio cd for your own use, such as an extra copy for the truck, without creating any problems. However, if you placed copies of the latest Sturgill Simpson cd for sale on Ebay, you would likely be contacted by the owners of the music regarding your unauthorized sale of their intellectual property.

Can I save seed of Clearfield varieties?
No, because Clearfield varieties are protected by a utility patent which protects a specific gene within the cultivar. Other examples of crop seed with genes protected by a utility patent include Roundup Ready, Bollgard, and Liberty Link. Wheat farmers will likely be seeing greater use of utility patents in the future but to my knowledge Clearfield varieties are the only hard wheat cultivars currently protected by a utility patent.

What about selling variety not stated (VNS) seed?
Not allowed. As indicated earlier, Title V of the federal seed act states that PVP-protected varieties can only be sold by variety name as a certified class of seed. This is one of several “ways-around-the-law” type questions that I am frequently asked at meetings and the answer is almost always no, you cannot do that. Other examples of violations would include: selling feed wheat, trading seed, giving seed away, and selling the standing crop of a PVP-protected variety and saving the seed.

The law just applies to the seller, right?
No. If there is a violation, then all parties involved can be included in the lawsuit. This includes the buyer, seller, seed conditioners, and even the entity spreading/planting the seed for the farmer.

How do I know if a variety is protected?
Certified seed of a protected variety will be clearly marked as such on the seed tag or the bulk label. The OSU Wheat Variety Comparison Chart indicates which varieties are PVP-protected and can be found at www.wheat.okstate.edu under Variety Testing, then under Variety Characteristics. Most varieties are now PVP-protected.

OSU is a public institution, why are they PVP-protecting varieties?
First and foremost, OSU acquires PVP-protection for new wheat cultivars to protect our (OSU, farmers, and taxpayers) collective investment in variety development. It takes 10 – 15 years to develop a wheat variety and this is not a cheap process. Without PVP protection others could reproduce an OSU wheat variety and profit from its sale without any benefit returned to farmers or OSU. PVP-protection ensures that when you buy an OSU variety, you are getting exactly the variety you are paying for and OSU has ensured quality-control standards through the certification process. It also ensures that a portion of the purchase price is returned to OSU for re-investment in the wheat breeding program where it is used to develop well-adapted varieties and ensure that the public sector remains competitive in wheat variety development.

Where can I find more information?
I am an agronomist, not a lawyer, so this article was meant to only hit the high points. A complete copy of the law (45 pages) can be found with a Google search of ‘plant variety protection act’. Texas AgriLife Extension also has a good summary of the law that can be found with a Google search for ‘plant variety protection act TAMU’.

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

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

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

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

 

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

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

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

 

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

 

Greenbugs were alive and well at Lamont

Greenbugs were alive and well at Lamont

Parasitic wasps were keeping greenbug populations under control in this field

Parasitic wasps were keeping greenbug populations under control in this field

Active and parasitized greenbugs on the same plant

Active and parasitized greenbugs on the same plant

 

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

 

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

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

A closeup of the damaged wheat head from the picture above

A closeup of the damaged wheat head from the picture above

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

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

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

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

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

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

Plant growth regulators for wheat

Wheat lodging is not generally a widespread problem in Oklahoma, but it does occur. Lodging occurs due to a variety of factors, and as shown in the figure below, the timing of lodging will determine the final impact on grain yield. Lodging at head emergence, for example, can cause as little as 30 or as much as 80% yield reduction. The numbers in the figure do not account for harvest losses, which can exceed losses associated with lower photosynthetic capacity shown in the figure.

Slide05

Freeze injury or disease can cause lodging due to stem failure, which is characterized by plant stems breaking near the base. I the absence of weakened stems due to freeze or disease, most lodging in wheat is caused by failure of the root anchorage system (root lodging). Root lodging occurs when the anchorage system of a top-heavy wheat plant is weakened due to moist soil and wind provides sufficient force to overcome the rotational stiffness of the root/soil complex. Research has shown that increasing the soil water content from 17 to 26% reduced the force required for anchorage failure by 33%, and as little as 0.25 inches of water plus 11 mph winds were enough to cause lodging. The thicker the wheat crop and/or the taller the wheat crop, the more force that winds exert on the root anchorage system and the greater the likelihood of lodging.

Severe lodging in an Oklahoma wheat field in 2013

In 2013 and 2014 we evaluated the plant growth regulator trinexapac-ethyl, which is sold under the trade name Palisade®. Palisade is a giberellic acid inhibitor and works primarily by reducing plant height. In our study we evaluated 12 oz/ac of Palisade with and without 4 oz/ac of Tilt (propiconazole) applied at Feekes GS 7 (two nodes visible above the soil surface). We included an untreated check and ALL plots, including the check, received 10.5 oz/ac of Quilt Xcel at Feekes GS 10.5 (heading). We conducted the trial at Stillwater (Irr), Perkins (Irr), and Chickasha (Non-Irr).

 

I provided 2013 results in a blog post last year, and this post provides an update including our 2014 findings. While application of Palisade resulted in numeric reductions in plant height at Chickasha and Stillwater in 2013, differences among treatments were not statistically significant. In 2014 application of Palisade or Palisade plus Tilt significantly reduced plant height at Chickasha and Perkins.

Wheat plant height as affected by plant growth regulators in 2013

Wheat plant height as affected by plant growth regulators in 2013

 

Wheat plant height as affected by plant growth regulator in 2014

Wheat plant height as affected by plant growth regulator in 2014

We rated plots for lodging at harvest using a 1 – 10 scale with 0 equaling no lodging and 10 equaling complete lodging.  Application of Palisade plus Tilt reduced lodging over Palisade alone at Chickasha. Application of Palidsade or Palisade plus Tilt resulted in numeric reductions in lodging scores at Stillwater in 2013, but the result were too variable to result in statistical significance. Palisade did not affect lodging at Perkins in 2013. There was no lodging for any site or treatment in 2014.

 

Lodging as affected by plant growth regulator in 2013. No lodging occurred in 2014 regardless of treatment.

Lodging as affected by plant growth regulator in 2013. No lodging occurred in 2014 regardless of treatment.

 

Application of Palisade or Palisade plus Tilt increased grain yield at Chickasha and had no effect on grain yield at Stillwater or Perkins in 2013. It is interesting to note that the Palisade treatment increased grain yield at Perkins in 2013 even though the plots lodged at comparable levels as the non treated check. My best hypothesis is that the treated plots lodged later than the non treated plots, as all plots were standing at anthesis (see picture below). Application of Palisade or Palisade plus Tilt increased grain yield at Perkins in 2014 even though there was no lodging. There were no differences in grain yield at Stillwater or Chickasha in 2014. Lodging occurred at Chickasha, but occurred later in the season.

Wheat grain yield as affected by plant growth regulator in 2013

Wheat grain yield as affected by plant growth regulator in 2013

Wheat grain yield as affected by plant growth regulator in 2014

Wheat grain yield as affected by plant growth regulator in 2014

 

To summarize our work, we found a trend for one to two inch reductions in plant height when Palisade or Palisade plus Tilt were applied, but this did not consistently translate to increased grain yield. Our results are consistent with other wheat plant growth regulator research, which has reported similar variation in response among sites and years.  The literature also shows that reduction in lodging is relative to the straw strength of the variety. That is, a plant growth regulator will not make a lodging prone variety stand like one with excellent straw strength, rather they will make it less prone to lodging relative to the same variety non treated.

Based on current evidence, plant growth regulators in Oklahoma are best kept on acres with high (> 80 bu/ac) yield potential that may have greater propensity for lodging due to variety or fertility.  If these high yield potential acres are being sprayed with a growth regulator at GS 7, the addition of a foliar fungicide might be prudent if it can be included at a relatively low cost. This early-season fungicide application will not, however, substitute for a fungicide application at flag leaf.

Full disclosure: Syngenta donated the product for this trial, but the only funding for the research was provided by the Oklahoma Agricultural Experiment Station and the Oklahoma Cooperative Extension Service. We conducted a separate trial evaluating Palisade in drought stress environments that was partially funded by Syngenta. The analysis and recommendations made in this blog post are based on research findings from 2013 and 2014 production years. Recommendations may change as further research is conducted and new information is obtained.

Checking for first hollow stem

First hollow stem occurs just prior to jointing and is the optimal time to remove cattle from wheat pasture. First hollow stem usually occurs in mid to late February in southern Oklahoma and early March in northern Oklahoma. Grazing past first hollow stem can reduce wheat grain yield by as much as 5% per day and the added cattle gains are not enough to offset the value of the reduced wheat yield.

Similar to previous years, we will monitor occurrence of first hollow stem in our wheat plots at Stillwater and report the findings on this blog. There is also a new first hollow stem advisor available on the Oklahoma Mesonet that can assist in determining when to start scouting.

Checking for first hollow stem is fairly easy.

  • You must check first hollow stem in a nongrazed area of the same variety and planting date. Variety can affect date of first hollow stem by as much as three weeks and planting date can affect it even more.
  • Dig or pull up a few plants and split the largest tiller longitudinally (lengthways) and measure the amount of hollow stem present below the developing grain head. You must dig plants because at this stage the developing grain head may still be below the soil surface.
  • If there is 1.5 cm of hollow stem present (see picture below), it is time to remove cattle. 1.5 cm is about the same as the diameter of a dime.
  • Detailed information on first hollow stem can be found at www.wheat.okstate.edu under ‘wheat management’ then ‘grazing’
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The plant on the left is past first hollow stem and is jointing. The plant on the right is at first hollow stem

The plant on the left is past first hollow stem and is jointing. The plant on the right is at first hollow stem

Potential for freeze injury

Temperatures are predicted to drop well below freezing tonight (14 April 2014), and there is high potential for freeze injury to Oklahoma wheat. I have posted an excerpt from K-State Extension Publication C-646 Spring Freeze Injury to Kansas Wheat along with a map which provides some rule of thumb temperature thresholds for the current Oklahoma wheat crop. Keep in mind these temperature thresholds are not exact, and temperatures closer to the soil surface might be higher than those reported by weather stations one meter above the soil surface, especially if moisture is present. Wheat in Oklahoma ranges from just past jointing to late boot and if forecasts are correct we will drop below the threshold temperatures where injury might be observed. The extent of injury will depend on how cold we get and how long we stay there. We can lose a few main tillers at this stage and still recover. Given our limited moisture and limited time prior to harvest, though, it is not likely that we will recover from a complete loss of tillers as we have after some March freezes in the past.

Excerpt from KSTATE publication C-646 Spring Freeze Injury to Kansas Wheat

Excerpt from KSTATE publication C-646 Spring Freeze Injury to Kansas Wheat

 

Approximate temperature thresholds for freeze injury to Oklahoma wheat on 04/14/2014

Approximate temperature thresholds for freeze injury to Oklahoma wheat on 04/14/2014

Freeze injury is not clearly identifiable until 7 – 10 days after the freeze event. So, the best advice for a wheat farmer after a freeze event is to find something else to do for a week or two and then check your crop. I have provided some pictures below with typical injury symptoms and rules of thumb regarding the extent of the injury. Fields should be checked at several random locations by splitting 10 – 20 stems at each location and looking for injury. Don’t focus solely on the large stems. Split a random sampling and determine the percent damage. A good reference for evaluating freeze injury to wheat is K-State Extension Publication C-646 Spring Freeze Injury to Kansas Wheat (access online by clicking here).

This is a healthy wheat head at approximately growth stage 6 - 7. Note the light green color and healthy, turgid appearance.

This is a healthy wheat head at approximately growth stage 6 – 7. Note the light green color and healthy, turgid appearance.

Freeze injury just after jointing. Note the pale, milky color of the head.

Freeze injury just after jointing. Note the pale, milky color of the head. Freeze injury to wheat heads at this growth stage is all or none, so this head is a complete loss.

Leaf tip burn from freeze injury will have no impact on final grain yield

Leaf tip burn from freeze injury will have no impact on final grain yield

Yellowing is a common reaction to light freeze injury. Wheat will recover quickly from this injury.

Yellowing is a common reaction to light freeze injury. Wheat will recover quickly from this injury.

Severe freeze injury at or just after jointing can turn the entire plant brown and fields can exude an odor similar to fermenting silage. If conditions are favorable, the plant can produce new tillers (as shown here) and make a partial recovery. It will take a few weeks after a freeze event to determine if the plant will recover from this type of injury

Severe freeze injury at or just after jointing can turn the entire plant brown and fields can exude an odor similar to fermenting silage. If conditions are favorable, the plant can produce new tillers (as shown here) and make a partial recovery. It will take a few weeks after a freeze event to determine if the plant will recover from this type of injury

It is common for sub-lethal freeze injury to result in bent or weak lower nodes. These plants might look fine, but will lodge during grain fill.

It is common for sub-lethal freeze injury to result in bent or weak lower nodes. These plants might look fine, but will lodge during grain fill.

Wheat streak mosaic virus showing up

Add wheat streak mosaic virus to the list of possible causes of yellowing wheat in Oklahoma. Wheat streak mosaic virus is transmitted by the wheat curl mite, which oversummers on grasses such as volunteer wheat and corn. The wheat curl mite cannot survive more than two weeks without a green host, hence the recommendation to make sure that all grass plants are dead two weeks prior to planting. You can find more information on the wheat curl mite and wheat streak mosaic in OSU Fact Sheet EPP-7328 – Three virus disease of wheat in Oklahoma

The photo below is from our wheat variety trial at Kildare. As you can see there is significant yellowing in some of the plots. Our first thoughts were that either wheat soilborne mosaic virus and/or wheat spindle streak mosaic virus were causing the symptoms; however, the yellowing was present in many varieties that are resistant to both these diseases. The Disease Doctor, Bob Hunger, collected samples for analysis in the OSU Plant Diagnostic Lab. Tests showed that wheat streak mosaic was the culprit.

Wheat streak mosaic virus is responsible for yellowing at our Kildare variety trial. All varieties are affected by the disease, but as shown in this picture the severity of the reaction differs somewhat by variety.

Wheat streak mosaic virus is responsible for yellowing at our Kildare variety trial. All varieties are affected by the disease, but as shown in this picture the severity of the reaction differs somewhat by variety.

We are facing this problem because I did not follow my own recommendations. While the plot area was mostly clean at the time of planting, there was some volunteer wheat present. We planted anyway and sprayed glyphosate right after planting. In the past wheat streak mosaic virus was primarily a northwestern Oklahoma issue and we could get by with late burndown on wheat ground in central Oklahoma. Our Kildare plots are a prime example that this is no longer the case. We have to control volunteer grasses (wheat, corn, grain sorghum, etc.) in a manner that will break the green bridge for at least two weeks prior to planting.

So, what is next for our plots at Kildare? There are some variety differences in reaction to the wheat streak mosaic virus. We will rate plots and include this information in our wheat variety comparison chart. I anticipate the plots will continue to go downhill and it is yet to be determined whether or not we will be able to harvest useable data from the location. We will certainly try again next year and apply our turndown earlier.