Over the past week we have seen some pretty cold weather throughout many areas of eastern Washington. Temperatures in the teens and low 20s with some below 10 degrees and often with associated wind have been observed. These freezing conditions have impacted plantings and some fields are looking very questionable.
In many cases, wheat plant crowns look white and healthy so we would expect the plants to continue to grow and recover. The damage appears limited to the leaves and these plants should turnaround quickly. We know plants and fields look bad to the producer, but it will change rapidly as the weather warms and returns to more normal temperatures.
One question to ask with injury like this is – what’s the soil temp at 1” and at 6”? That will help determine how fast things might start growing. Tim Murray checked plots Tuesday 4/14 and 6” soil temps ranged from 42° to 51°F, so it’s going to be longer for the plants at low temp to start regrowing.
We caution against making rash decisions without critical analysis of the situation. Most plants will likely recover and will have a better chance of production than reseeding with a spring crop. Inspection of plants is critical. If the plants have already jointed then the growing point is aboveground and more vulnerable to injury by the freeze.
There are several good reference materials available on the internet. Kansas State University has a nice Extension publication on Spring Freeze Damage in Wheat.
Much of the wheat in eastern Washington is in the tillering stage with some fields starting to joint. The location of the plant’s growing point is important. During the tillering stage the growing point is below or near the soil surface and somewhat insulated from cold air temperatures. Consequently, damage during the tillering stage is primarily limited to the leaves, which become twisted and light green to yellow in color and are necrotic (burned) at the tip within one or two days after freezing. Injury at this stage slows growth and may reduce tiller numbers, but growth of new leaves and tillers usually resumes with warmer temperatures.
Unusual patterns of yellowing and necrosis can occur on the affected plants. These patterns tend to be consistent in different individuals of damaged wheat making the damage pattern more regular than those caused by pathogens and pests (image 1). Cool temperature damage can be wide spread across multiple fields and varieties. Damage across fields can be uneven and with low spots and shaded areas more likely to experience cold damage (image 2).
Other crops have also experienced cold damage. Canola can become distorted with thickened mid-veins. A common symptom on many different types of plants, including wheat, is dark, translucent tissue (image 3 and 4). Much of the early seeded spring canola had emerged has had some severe damage. Please keep a close watch on the field(s) affected because it does not take many canola plants per square meter to fill in and produce an average to better yield. Some canola is probably still about to emerge so this is a waiting game. Remember it is only mid-April.
Image 1: The necrosis on these stems is a result of cold damage. The lesions occurred consistently at the third node—this type of repeated and regular pattern is more typical of abiotic damage than of a pathogen. The wavy peduncle on the right side is also common for cold damage.
Image 2: Large area of a field showing similar symptoms of discolored, and slightly wilted plants.
Image 3: Wheat damaged by cold temperatures with dark, desiccated leaves. Notice how the crowns are healthy.
Image 4: Close up of the cold affected leaves: symptoms include dark discoloration, desiccation, and necrotic lesions.
A special thank you to Drew Lyon, Steve Van Vleet, Rachel Bomberger, and Tim Murray for their contributions to this post.