On April 19th winter weather returned and temperatures across most areas dropped to 28 degrees and below for several hours. The next few days look like this could repeat again . The growth stage the wheat is in will dictate the amount of damage we see to this crop. When wheat is just beginning to joint the plant can withstand temperatures down to 20 degrees. But when wheat is in the jointing to the boot stage, temperatures below 30 will quickly damage the plant. Depending on your location, and the development stage of your crop, producers may notice damage. Damage may take 10-14 days to show in your wheat crop. A light freeze will just damage the leaf tips and minimal losses in yield will occur. With more severe freezing, the entire leaf can turn yellow and the plants will look wilted. Within a few days there will be a silage smell present. If you suspect damage, we need to report this claim now to the adjusting staff. I would caution producers not to be too hasty in wanting to destroy a field. Most times the damage will be superficial. Yet other times the crop will continue to get worse as time progresses. Whenever an adjuster comes to appraise a field, be it for crop failure, damage, or silage, they are making a determination of that crop’s yield potential on the day of the appraisal. By waiting several days the condition of the plant may change either for the good or the bad. If a producer chooses to destroy a crop we would always recommend leaving a sample strip as instructed by the adjuster to be appraised at a later date. There is a lot of time between now and harvest for other issues to affect the crop. Remember when leaving strips, use care not to spray over them if going to a different crop as adjusters will need to appraise these strips again. DO NOT SIGN AN APPRAISAL SHEET UNLESS YOU AGREE WITH THE ADJUSTERS DETERMINATION. When you sign the appraisal sheet, that makes the appraisal final and you won’t be able to reappraise the crop later, in the event that the damage was worse than originally thought. When in doubt of an appraisal always ask the adjuster questions or feel free to call our office.
The following article has been reprinted with the permission of OSU. Spring freeze on wheat- What did this crop in temperature do to my wheat crop? Amanda de Oliveira Silva, Small Grains Extension Specialist
Temperature has dropped low enough in the past hours throughout some areas of the state to potentially cause some level of injury to the wheat crop. There were several areas that spent at least a couple hours with temperatures in the mid to lower 20s 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 wheat plants to freeze injury steadily increases as we progress through the spring from jointing to heading and flowering. Figure 3 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. 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 to assess freeze injury. The extent of a significant freeze event may not be apparent 1 or 2 days after. If warm temperatures return quickly, you should 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. 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.
The most important plant part to check is the growing point (i.e. the developing head)! This will be important for areas of the state that have fields with plants that 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). 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. Freeze during the flowering stage may result in sterility via death of the anthers (male organ) and consequently poor kernel set and grain yield losses. 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. Also, the percent of damaged heads may not translate into percent yield loss. There is still opportunity for wheat at the jointing stage 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 more difficult to make this type of recovery.
What is the relationship between soil moisture and freeze injury? 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 and freeze injury needs to be checked on a field by field basis. 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.