Bob’s neighbour informed him that he’d just finished arranging for a sprayer operator to spray one of his fields for a flea beetle infestation. Within the hour, Bob was scouting his own canola field, which was located next to the flea beetle-infested field. He found signs of flea beetle damage that hadn’t been there the previous week. I arranged to meet Bob, who farms 3,000 acres of peas, wheat and canola near Kelvington, Sask., to assess the damage to his crop.
The weather in this area had been cold and wet. However, June’s temperatures were proving warmer, and had heated up substantially during the previous week. Under cold and wet conditions the mobility and feeding of flea beetles is limited. Now it appeared they were on the move!
The leaves of the canola plants adjacent to Bob’s neighbour’s field had symptoms of flea beetle feeding. The leaves were notched at the edges, and the surfaces had small circular pits. It didn’t take long to find the small black beetles feeding on some plants’ leaves.
Bob’s crop was well into the three-leaf stage. The damage caused by the beetles was most severe at the periphery of the field near his neighbour’s infested field. I estimated the feeding damage to the true leaves at 20 per cent.
“I was really hoping to avoid the extra cost of spraying this year,” Bob said.
“I don’t think it’s come to that yet,” I said. “The damage to this field is still just below the economic threshold — which is an average defoliation of 25 per cent. Your field is also more advanced in its development than your neighbour’s crop, which had only reached the first true leaf stage. The plants in this field should overcome and outgrow any damage caused by the beetles.”
You will have to monitor this field closely,” I told him. “As long as conditions for plant growth remain favourable, your crop should be fine.”
Good rotation strategies and the use of seed treatments will help Bob protect his canola crops from flea beetle damage in the future.
As predicted, Bob’s canola crop outgrew the damage and his yield was right on target. †