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Amanda de Oliveira Silva, Small Grains Extension Specialist
It has been almost one month since the freeze event on April 21, and we are now obtaining a better picture of potential freeze damage on wheat fields across Oklahoma. As I have indicated, the extent of the freeze damage will depend on several factors, including the growth stage of the plants, how low the temperature will get, and how long it stays at those cold temperatures. Wheat growth stage ranged from flag leaf emergence to heads starting to or fully emerged when the freeze occurred, and number of hours and temperature varied across the state (Figure 1).
Traveling around the state for plot tours these past weeks, I have seen and heard about damage ranging from minimal to quite severe. Some fields seem to be fine with only scattered damaged heads and the grain appears to be filling as expected. Other fields however, show much more significant damage with discolored and sterile heads.
At the plot tour at Chickasha on April 30, there was a mix of freeze and hail damage with several abnormally growing heads (due to head trapping). Anthers seemed to be fine at that point (Figure 2).
On May 7, I checked some wheat fields around Sentinel with Gary Strickland (Jackson County Extension Educator and SW Regional Agronomist) and we observed almost no freeze damage with a few heads in the field showing a pale color and partial sterility (Figure 3). I have observed this symptom commonly in fields I have visited, and many producers have described this to me as well. Although common, it typically has been found at a low incidence.
We observed a few spots with freeze damage while at Alva on May 12, especially in low spots of the field and on the tops of terraces. Again, relatively few spots in the field showed damage. The wheat was looking good at Alva, but really needing a rain (Figure 4).
The most severe freeze damage that I have seen so far was yesterday near Morris in eastern OK. The heads were green but there was no grain present (i.e. sterile). Damaged heads had glumes with a chocolate discoloration, which is similar to the discoloration caused by the bacterial disease called black chaff. In some cases, Dr. Hunger and I felt these discolored heads were the result of this bacterial disease but that the majority of the heads showing these symptoms were the result of freeze damage (Figure 5).
At the plot tour at El Reno today, we also observed a few varieties with pale colored and “empty” heads due to the freeze (Figure 6). We observed more freeze damage on wheat that was planted earlier and grazed as compared to the grain-only (ungrazed) wheat in that same field. Another noteworthy item is related to my earlier observation that the February freeze hurt some of the varieties in the dual-purpose plots by severely reducing tillering that would cause a loss of stand. That observation in those varieties was confirmed as the stand loss was quite evident today.
In conclusion, the freeze damage I am seeing is variable within and across fields, but overall I would say is minimal in most of the state. However, continue to keep scouting as it will now be easier to identify freeze damage.
Please let me know what you are seeing out there! My email is firstname.lastname@example.org.
Also, contact your County Extension office for more information.
Amanda de Oliveira Silva, Small Grains Extension Specialist
Temperatures dropped below freezing in the past hours in northwestern Oklahoma and Panhandle (Figures 1 and 2), and freezing temperatures are expected across most of the state tomorrow morning (April 21) (Figure 3). There is a potential for freeze injury to Oklahoma wheat. The extent of that will depend on several factors, including the growth stage of the plants, how low the temperature will get, and how long it stays at those cold temperatures.
What are the temperatures that can damage the wheat plants?
This will depend on the growth stage of the plants. Anecdotal evidence suggests 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 wheat plants to freeze injury steadily increases as we progress through the spring from jointing to heading and flowering. Figure 4 below is a general guide to the minimum temperature threshold and its impact on yield. Keep in mind these temperature thresholds are not exact but provide a decent rule of thumb. 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. It is difficult to have exact numbers because each freeze event is unique. While a field at the jointing stage could spend two hours at 24 F, it is possible that the same amount of injury could occur at a 28 F temperature that was sustained for a more extended period.
How long should I wait to assess the injury?
Another important thing to keep in mind is that we need to be patient before 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. Suppose temperatures remain cool after the freeze event. In that case, it may take 10-14 days before the extent of the injury can be fully assessed.
What are some freeze injury symptoms to look for?
A typical freeze injury symptom is leaf tips turning yellow and necrotic (Figure 5). 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 6). You may even notice a “silage” smell after several days.
The most important plant part to check is the developing head (i.e., growing point)
This will be important for areas of the state with fields with plants at flag leaf emergence stage. Sometimes we can see what look like healthy plants overall, but the developing head has been damaged or killed. To get a look at the developing head, you can slice the stem open lengthways. A healthy growing point will have a crisp, whitish-green appearance and be turgid (Figure 7). 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 8, right). Another indication that the growing point has been compromised is that the next emerging leaf is necrotic, and the lower stems are discolored, with lesions and enlarged nodes.
Freezing at the boot stage may cause the head to be trapped by the sheaths of the flag leaf resulting in issues with head emergence (Figure 9). The whitish tips of the awns indicate that it was exposed to freezing temperatures and that the flower parts could have been compromised. Freeze during the flowering stage may result in flower sterility via the death of the anthers (male organ) and consequently poor kernel set and grain yield losses (Figure 10).
Also, the percent of damaged heads may not translate into percent yield loss. For example, there is still an opportunity for wheat to produce additional tillers and/or retain secondary tillers at the jointing stage. Whether or not these tillers can 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 (which is the case for most Oklahoma wheat), it will be more challenging to make this type of recovery.
A few points to consider:
Every freeze event is unique and freeze injury needs to be checked on a field by field basis – the temperatures and time durations we use regarding freeze injury are rules of thumb and are not exact. I have seen instances where conventional wisdom would indicate complete crop loss, and we skate through with minimal damage.
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.
It will take a few days to see how bad things are – Symptoms may start to appear mid-next week and will likely be identifiable by the end of the following week. Healthy wheat heads will remain turgid with a green color. Damaged wheat heads will be bleached, yellow, or brown and will easily break when pushed against.
Contact your local Extension office.
Amanda de Oliveira Silva, Small Grains Extension Specialist
I have been watching some wheat fields consistently after that ice storm came in late October. I am currently seeing anything from good looking wheat fields to areas with incomplete, thin, and uneven stands. We might not see complete stands for a while as the wheat emergence seems to be very uneven, and the wheat is still slowly coming up (Figure 1).
The thin and uneven stand establishment of the current wheat crop is likely due to the severe drought from the end of September to most of October. Then, most of Oklahoma was hit by the ice storm during the last week of October, with some areas receiving up to 5 inches of rain. Although that rain came in a much-needed time, it could have created a crust in the soil preventing the coleoptile from breaking through the soil surface.
If the wheat fails to emerge as expected in your field, dig up the soil and look for an “accordion” like plant. If you see that wheat has emerged its first true leaf under the soil surface, and it has been sitting there for a week or more, it will probably not going make it (Figure 2).
However, I am seeing crinkled coleoptiles in fields around Stillwater that are coming up slowly and will be fine. The crinkles probably occurred when the heavy rain occurred during the ice storm, but it was not enough to prevent the coleoptile from continuing to grow and pushing through the soil surface for the most part (Figure 3).
Overall, our variety trials that were planted sometime in October are coming up nicely, but we might not have a complete stand for a little while in some locations. Robert Calhoun, the Senior Agriculturalist of OSU Small Grains Program.
Some fields that were planted in early-mid October is also just now starting to emerge near Kay County. Shannon Mallory, Kay County Extension Educator.
About 95% of the wheat in our variety trial at Altus has emerged and shows adequate stands (planted on September 29). Gary Strickland, the Jackson County Extension Agriculture Educator and Southwest Research and Extension Center Regional Agronomist.
Josh Bushong, the OSU Area Extension Agronomy Specialist, reported in his Ag Insights November report that most of the fields in the North Central region are showing thin and uneven stands. He also mentioned this would likely have a small effect for grain only-producers.
As a summary, most of the fields that I am seeing or hearing about that were planted in October are still coming up. Wheat growth is a function of temperature. The cooler temperatures and lower cumulative growing degree days in the coming months will slow down growth until March or so. Plants may compensate to a certain extent for that reduced stand, and wheat producers aiming for grain-only production should not be concerned yet.
By Tom Royer, OSU Extension Entomologist
I have received several reports of (and photos, Figure 1) of bird cherry oat aphid (BCOA) numbers in winter wheat that will require treatment with an insecticide
Bird cherry oat aphids are small (2mm) olive-green aphids with a red-orange patch surrounding the base of each cornicle (Figure 1). Old, wingless, overwintering adult aphids are darker, almost black. At this time, you may also find winged aphids that have moved in to the field (Figure 2).
What are my suggestions regarding control of bird cherry oat aphid in winter wheat?
- Unpublished research provided by Dr. Kris Giles (OSU) and Dr. Norm Elliott (USDA-ARS) along with studies conducted in South Dakota, Minnesota, and North Dakota on spring wheat indicated that BCOA causes yield loss before wheat reaches the boot stage. Approximately 5-9% yield loss occurs when there are 20-40 BCOA per tiller (average 7%).
- Visible damage from bird cherry-oat aphid is not very noticeable so infestations may go unnoticed. It is very important to check fields for infestations and make treatment decisions only after a field has been checked.
My suggestion for making a treatment decision is as follows:
If greenbugs and bird cherry oat aphids are both present, use Glance n’ Go to scout, which can be accessed at http://entoplp.okstate.edu/gbweb/index3.htm. Published research from Giles and Elliott showed that Glance n’ Go sampling will work with both aphids if they are both present.
If bird cherry-oat aphid is present alone, count the number of aphids present on each of 25 randomly-selected tillers across a zigzag transect of the field. The reason that you can’t use Glance n’ Go is that the most available research suggests that the threshold is too high to effectively use Glance n’ Go.
Look for evidence of parasite activity in the form of mummies (Figure 3). A rule of thumb is that if 5-10% of the aphids are mummies, more than 90% are already parasitized. If mummies are not present, use the guidelines below to make a treatment decision.
If, after thoroughly scouting your field, you can identify that infestations are spotty, consider spot spraying with a ground rig.
Use the YIELD LOSS TABLE to determine a potential YIELD LOSS from the aphids. Then estimate your CROP VALUE and calculate your CONTROL COSTS. Use those numbers to estimate PREVENTABLE LOSS. If estimated PREVENTABLE LOSS is greater than CONTROL COSTS, Treat; otherwise, Don’t Treat.
Here is an Example:
Step 1: Estimate YIELD LOSS:
- Total # aphids_______525___________/25 tillers = average # aphids/tiller_____21_____
Step 2: Estimate CROP VALUE: (Crop Value = Yield potential X Price per bushel)
- Yield potential__40____ bushels/acre X price per bushel $____4.50____ per bushel
CROP VALUE = $___180____
Step 3: Estimate CONTROL COSTS: (Control Cost = Insecticide Cost + Application Cost)
- Insecticide cost $___6_____ /acre + Application Cost $ ____3_____/acre
CONTROL COSTS $_____9_____/acre
Step 4: Estimate PREVENTABLE LOSS (Crop Value X Yield Loss from Aphid)
- Crop value/acre $___180_____ x Yield Loss from aphid ___0.07_____
PREVENTABLE LOSS $____12.60______/acre
IF PREVENTABLE LOSS $___12.60_____ is greater than CONTROL COSTS $___9.00_____ TREAT
IF PREVENTABLE LOSS $________ is less than CONTROL COSTS $__________ DON’T TREAT
Check CR-7194, “Management of Insect and Mite Pests in Small Grains” for registered insecticides, application rates, and grazing/harvest waiting periods.
It can be obtained from any County Extension Office, or found at the OSU Extra Website at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2601/CR-7194web2008.pdf
Temperatures over the weekend were cold enough to cause injury to the Oklahoma wheat crop. As shown in the figure below from the Oklahoma Mesonet many areas of Oklahoma spent several hours below 28F. While temperatures in the wheat canopy might have remained slightly higher than reported air temperatures, they were still probably low enough to result in significant injury to wheat.
A few points I would encourage everyone to consider:
Every freeze event is unique – the temperatures and time durations we use regarding freeze injury are rules of thumb and are not exact. I have seen instances where conventional wisdom would indicate complete crop loss and we skate through with minimal damage.
It will take a few days to see how bad things are – Symptoms may start to appear later this week and will likely be clearly identifiable by the end of this week. Healthy wheat heads will remain turgid with a green color. Damaged wheat heads will be bleached, yellow, or brown and will easily break when pushed against. I anticipate that we will not have any partial “blanking” of wheat heads and that most wheat heads will either be okay or a complete loss. This post from last year has some pictures showing tell tale signs of freeze injury. The linked post also serves as a reminder that while freeze is the concern of the day, the potential worsening of drought conditions in NW Oklahoma has the potential to do far more damage.
% damaged heads might not = % yield loss – It is still relatively early in the growing season and there is still opportunity for smaller (two nodes or less) wheat 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 moisture and weather. IF (and that is a big if) weather conditions remain favorable, late emerging tillers in central and northern Oklahoma might still have a shot at producing grain. It will be tougher for more advanced wheat in southern Oklahoma to make this type of recovery.
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’
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.
No, this blog post is not about a get rich quick scheme, but there is a way for the average wheat farmer in the southern Great Plains to add $50,000 to $100,000 to the bottom line in a single day. Many soil tests I have pulled have shown as much as 50 to 90 lb/ac of NO3-N in the top 18 inches of soil. Ninety pounds of N equates to about $45 of N fertilizer, and this knowledge could save a 2,500 acre wheat farmer in excess of $100,000 in fertilizer cost. Soil testing is laborious, but the potential economic returns for spending a day or two soil sampling are outstanding.
There is still time to soil sample. Soil samples only take a few days to process once they are in the OSU lab. It is not unusual for transit time to the lab to the slowest part of the process, so if you need a fast turnaround a trip to drop samples in the Ag Hall basement in Stillwater will help (plus you have probably been wanting cheese fries). If you have already applied pre-plant fertilizer or sown wheat, there is still time to assess soil N availability and uptake via the N-Rich Strip. In its simplest form, the N-rich strip is an area where N is not limiting. Either by visual assessment or with the assistance of an optical sensor, you can use the N-rich strip to determine your top dress N requirement, but you must create the N-rich strip this fall.
The bottom line is that a day of soil testing or putting out N-rich strips is well worth your time investment. On another note, how would you like to make money and improve your health at the same time? I have a multi-level marketing opportunity that I can get you in on the ground floor, but don’t tell anyone else. I can only make this deal for you and only today. There will be a small “buy in” fee that you will need to pay cash up front, though.
Partial funding for the research included in this blog post was provided by USDA Project No.2012-02355 through the National Institute for Food and Agriculture’s Agriculture and Food Research Initiative, Regional Approaches for Adaptation to and Mitigation of Climate Variability and Change
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’.
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.
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.
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.
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.
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.