Producers in different parts of South Dakota have reported freeze injury on winter wheat over that last couple weeks.
SDSU Extension West River Agronomist Thandiwe Nleya said producers should monitor the crop carefully over the coming days to assess the extent of damage and make decisions on management options available.
"The critical temperatures at which damage to winter wheat can occur are 12 degrees if the crop is at tillering stage, 24 degrees if it is in the jointed to early boot stage, and 28 degrees if the crop is in the late boot to head emergence stage," Nleya said. "However, the degree of damage to the crop is also influenced by the duration of low temperatures. Prolonged exposure to low temperature causes much more injury than brief exposure to the same temperature."
To evaluate the damage producers need to carefully monitor the crop three to five days after the low temperature event. It is also important to note that cool weather after freezing temperatures may delay the appearance of injury symptoms, she said.
Nleya offered this advice:
If the crop is at tillering stage, the growing point is just below the soil surface and is usually protected from injury unless the ground freezes. Most of the damage will therefore occur to the leaves which turn yellow in color and show burning at the tips within one to two days after freezing. Injury at this stage will slow down growth and reduce tiller numbers. At this stage, growth of new leaves and tillers usually resumes with warmer temperatures and yield reduction due to freeze injury is usually slight.
At jointing stage, leaves will show similar symptoms as the tillering stage, but the most serious injury at this stage occurs to the growing point. Locate the growing point by splitting the stem. A normal growing point is bright yellow-green; a damaged growing point is white or brown and water soaked in appearance. Yield reduction will depend on the extent of injury.
If the crop is at boot stage, look for injury on the small head, which can be found above the top node in the stem. A healthy head should be white or light green. The amber or watery appearance would indicate freeze damage.
Freezing usually injures part of the wheat head or only plants in certain parts of the field especially depressions or low areas. Where main tillers have been damaged, secondary tillers may grow and enhance the stand. The general rule is that if you have 50 percent of your plant stand or more the stand is adequate. If damage to the crop is widespread producers may consider abandoning the crop. Nleya stressed that producers should remember to check with their crop insurance adjusters before they re-seed.
Producers abandoning the winter crop may also want to consider re-seeding to other crops. The most likely crops in western South Dakota are milo, millet and sunflowers. Other possibilities include soybean and corn.
"Growers should take into consideration the moisture situation and make the decision to re-seed based on whether there is adequate soil moisture for the alternate crop. Otherwise, the land with the injured wheat can be summer fallowed and replanted to wheat in the fall," Nleya said. "Finally, I must emphasize the fact that before producers destroy the freeze-injured winter wheat crop and decide to plant another crop they should consider the production costs they have incurred and the cost of producing the new crop."
More information on freeze injury to winter wheat is available from Kansas State University Research and Extension publication C646, "Spring Freeze Injury to Kansas Wheat." Find it online at www.oznet.ksu.edu/library/crpsl2/c646.pdf.
- SDSU AgBio Communications.