It’s the time of year when crop scouting pays big dividends

Weed escapes, herbicide resistance, disease, and pests can all be assessed after spraying, says expert

These Manitoba Department of Agriculture photos show that weeds are more obvious when looking 
down at a wheat crop (r) than looking at it sideways.
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Spray, then scout, says provincial crop specialist Mark Cutts.

“It is very important to recognize that scouting after a herbicide application is vital to weed control, said Cutts. “In the majority of cases, producers will find that the chemicals have worked. However, in certain situations, field scouting may show the weeds weren’t properly controlled. Producers can start to evaluate what might have caused the problem.”

A difference in the pattern of weed escapes can indicate poor performance of a herbicide due to environmental conditions or that herbicide-resistant weeds may be present.

“If the weeds that escaped the herbicide application are found throughout the entire field, it can point to limited herbicide effectiveness due to environmental conditions such as low temperatures,” said Cutts. “However, if the weeds are found in isolated patches, it may be a herbicide-resistance issue. If unsure of the cause, contact an agronomist or chemical company representative to discuss the possible causes of the weed escapes.”

Scouting also allows disease development to be assessed.

“For example, barley leaf diseases such as scald and net blotch move from the older leaves to the newer leaves as the growing season progresses,” he said. “If leaf diseases are present and environmental conditions remain favourable for disease development, a fungicide application may be necessary once the crop has reached the flag-leaf stage.”

Producers can scout for recently emerged insects. For example, as head emergence occurs on wheat crops, they should be monitored regularly for wheat midge.

“As flowering starts in canola, producers can start to evaluate the presence of cabbage seed pod weevil,” said Cutts.

For information on economic thresholds for insect pests attacking oilseeds, cereals, and forages, go to (search for ‘economic threshold’).

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