While snow cover insulates winter wheat from brutal cold, some parts of the state were hit with sub-zero temperatures when wheat was exposed. In that situation, the crop can suffer a number of injuries that force growers to decide whether to go ahead and apply nitrogen or terminate the crop.
“Whether wheat is at risk depends on where it’s located in the state,” Shaun Casteel said. “The snow blanket protected the crop in some areas, but in others, particularly in the southern part of the state, we didn’t have that snow cover.”
Even though winter wheat enters dormancy for the cold months, temperatures below 12 degrees Fahrenheit sustained for more than two hours can cause freeze injury to exposed wheat. As the crop advances into the jointing growth stage, the temperature point of injury doubles to 24 degrees.
Injury can be as minor as leaf-tip burn or as major as growing-point termination.
In areas that had some soil freezing and thawing cycles, the wheat crop also is at risk for heaving, a phenomenon where water refreezes in soil pores, lifts the soil, pushes the plants up and exposes the roots to drying out.
A third type of winter injury, Casteel said, is smothering. Wheat most at risk is that which is growing in low-lying field areas that ponded when snow melted, then froze again.
“We had a thaw a couple of weeks ago that caused some ponding,” he said. “When ponded water freezes it cuts off the oxygen to the wheat roots underneath. Even though the wheat is dormant, it’s still respiring, so cutting off oxygen can cause plant death.”
Wheat will start to break winter dormancy once temperatures consistently reach the mid-30s and 40s. At that point, growers will have a better idea of how the crop fared over the winter.
But for some farmers who prefer to topdress nitrogen fertilizer when the ground is still frozen, waiting until green-up presents other challenges.
“Growers have to decide whether they want to spend the money to topdress wheat that might not be alive, or if they want to wait until green-up and then risk having to topdress nitrogen on soggy soils,” Casteel said.
Another option is to topdress a lower nitrogen rate now, observe wheat condition at green-up, and then topdress liquid nitrogen at the jointing growth stage if wheat is viable. Casteel said that while this option isn’t ideal, it is possible.
For farmers who find that wheat is in extremely poor condition, Casteel said it might make sense to tear out the crop and plant a spring cash crop such as corn or soybean.
“There are some bad-looking fields out there that were exposed to extreme cold with no snow,” he said. “Some of those fields are completely brown, which means they don’t have any green tissue for photosynthesis.”
More information about winter injury to wheat and wheat production in general is available in Purdue Extension’s Wheat Field Guide. The guide is available for $5 from Purdue Extension’s The Education Store by searching for “ID-448.”