Some growers are reporting high numbers of adult flea beetles. Adults emerge from pupae in late July and August and overwinter to feed on young canola seedlings the following spring. These same adults do feed now, but Julie Soroka and Larry Grenkow (Can. J. Plant Sci. 2012: 97-107) found that flea beetle feeding on canola in late-summer is rarely an economic concern.
In the report, they wrote: “Flea beetle feeding that occurs when seeds in lower pods of canola are at the green stage or beyond is unlikely to affect seed yields regardless of the infestation rate of flea beetles. Even when seeds are translucent to green, numbers higher than 100 flea beetles per plant, and for some cultivars higher than 350 per plant, may be necessary to cause significant yield reductions.”
Interestingly, last week it seemed most flea beetles observed were the all-black crucifer type. AAFC research scientist Bob Elliott says striped flea beetle adults have been hatching this summer in high numbers, and he says they are often throughout the canopy. You may just have to look a little harder to find them, he says.
Insects are less of an issue this week as many canola crops close in on harvest. Pre-harvest intervals also become an important factor in the decision. One risk is that mobile insects could be concentrating in the latest crops that still provide a green food source. Keep a close eye on late canola crops.