A spring of extremes — first cold, dry and windy, then hot, dry and windy — has resulted in weeds getting a head start in many soybean fields in the soybean-growing areas of Western Canada.

While wind and cold temperatures delayed burnoff applications at the start of the season, questions about when to spray in extreme, hot conditions have become common with the arrival of a major heat wave over the last week.

“The heat of the day is challenging, as if you’re up over 28 degrees you can get additional crop injury and plants start to shut down,” explains Harold Brown, technical service specialist with BASF in eastern Manitoba, in this weed control-themed Soybean School episode.

From a temperature perspective, early morning and late evening are usually more ideal than the heat of the day. But when we’re talking about managing hard-to-control weeds in soybeans, such as glyphosate-resistant kochia, the conversation often involves dicamba, and dicamba is at risk of drift due to inversions.

“We’re saying don’t spray in the heat of the day, so maybe in the cooler parts of the evening or early morning, although you can have some challenges with inversions, so there’s not a simple answer,” notes Brown. “Maybe the best thing is to delay spraying if the weeds are really small until after this hot weather has gone by.”

Brown discusses the process of deciding when to spray amidst challenging weather with oncoming weeds, crop staging, and more in this Soybean School episode:

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