Unusual growing season brings unusual pest pressures

Weather conditions have brought late weed flushes and repeat attacks on crops, says specialist

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This year’s unusual weather is causing pests such as weeds, fungal diseases and insects to emerge at unexpected times, says a provincial crop specialist.

A dry spring, a later arrival of rain, and a cooler-than-normal growing season all played a role, said Neil Whatley.

“While some producers waited for rainfall prior to seeding, most planted their crops in a timely fashion and some experienced only partial seed germination,” he said. “When rainfall occurred several weeks later, the remainder of their crops germinated, creating variably maturing crops.

“Later rainfall also caused later weed flushes. The unusually cool growing season has resulted in less overall heat units and therefore, slower crop maturity. Depending on heat units during the month of August, crops may or may not mature rapidly.”

Variable maturity means crops are vulnerable to similar pests more than once, he added.

“It may be tempting to apply a herbicide to control a later-emerging noxious weed in a crop prior to the weed forming seed,” said Whatley. “Continuous rainfall over an extended period causes fungal diseases to do more damage to developing crop heads and pods with ensuing damage to seeds. The bertha army worm can be problematic at a later stage of canola development even under normal conditions.”

But it’s important to review a pesticide’s rate, timing and PHI (pre-harvest interval) prior to its application, he said. A PHI is the number of days allowed following a pesticide application and the harvest of crops for edible consumption.

“There should be no trace of chemical remaining in the seed, so an interval — established through research — refers to the number of days required for a chemical residue to disintegrate in the plant. Depending on the crop or pesticide type, interval periods vary. Harvest is defined when the crop is initially cut by either swathing or direct combining. Post-cutting field activities and grain storage are not included in the interval.”

PHI guidelines can be found on Keep it Clean’s website.

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