Frost damage to soybeans depends on crop stage

Frost damage to soybeans depends on the stage of the soybeans and how cold it gets and for how long, according to a pulse crops extension specialist.

Frost is possible Tuesday evening and Wednesday morning in parts of Manitoba.

Soybean growth stage is determined by examining the pods, Terry Buss of Manitoba Agriculture at Beausejour said in an email Tuesday.

“It is all about the pods, so don’t get distracted by the condition of the leaves,” he wrote. “The more advanced/mature the soybeans pods are, the less the potential yield loss.”

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Manitoba Pulse and Soybean Growers has a maturity guide on its website, with excellent pictures and descriptions of the growth stages. Use it as a guide in determining crop stage, he wrote.

The following is Buss’ yield loss guide:

  • Frost during the R5 stage can reduce soybean yield by 50 to 70 per cent;
  • R6, expect a 20 to 30 per cent loss;
  • R7, about a five per cent reduction;
  • at the R8 stage, no yield loss is expected.

DuPont Pioneer has a factsheet on frost-damaged soybeans, Buss wrote.

“You will always find some variation around predictions of yield losses due to frost in soybeans,” Buss wrote. “This is to be expected. There is no absolutely right answer.

“No crop is uniformly at one growth stage and every frost event is unique in how it plays out. The information above is merely meant to serve as a guide for our expectations.”

— Allan Dawson is a reporter for the Manitoba Co-operator at Miami, Man. Follow him at @AllanReporter on Twitter.

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