If you’re growing canola or mustard this year (or garden vegetables like broccoli or cauliflower) you might need to be concerned about the flea beetle, says Scott Hartley, provincial insect/vertebrate pest management specialist for Saskatchewan. Climate conditions matter, though, when it comes to certain pests, and the flea beetle is no different. “If it’s going to be warm and dry, like we had in 2015, then flea beetle populations will be favoured.”
Flea beetles, like grasshoppers, don’t do well in wet or moist conditions. “They can suffer from diseases and fungus,” says Hartley, and they just don’t flourish in the same way as they do when conditions are dry.
Most seed varieties in this day and age are hybrid varieties “that come with a seed treatment, which includes an insecticide for control of flea beetles,” says Hartley. “So flea beetles should be covered; but, you can still have issues, like last year, in 2015, we hadn’t seen flea beetles for a decade before that — we had low populations in most areas, because of moist, cool conditions — but last year’s dry conditions favoured flea beetle’s reemergence.”
Even though many seeds do come with insecticide for flea beetle prevention, that treatment will only be effective for a finite amount of time, says Hartley. If climatic conditions cause the delay of growth of plants, the in seed insecticide can wear off.
Last year, for example, seeds were planted, but growing conditions weren’t great, so the plants took their time coming up, says Hartley. Some farmers planted early in 2015, in late April or early May because temperature conditions in previous years warranted it; but then even though spring was warm in 2015, evenings were very cool and frosty in some areas, which delayed growth.
This can be an issue for flea beetle treatment. “If the plants haven’t grown through the earlier cotyledon stage and a bit more, the chemical in the seed can be wearing off, that’s when an insecticide control spray may be required.”
“In the spring, producers should monitor and assess damage to cotyledons and the first true leaves on canola, rapeseed and mustard seedling for the first 14 days after emergence, especially on sunny, calm days when temperatures exceed 14 C,” according to Manitoba Agriculture, Food and Rural Development’s website. Checking on seedlings early is very important because flea beetle damage can be swift. Once you know what you’re dealing with, you can better plan your approach for management.
Hartley sees a situation where 25 per cent of leaf tissue is being damaged or destroyed as the threshold for using an insecticide.
Hartley says that there’s been a fair bit of research done by Agriculture and Agri-Food Canada on flea beetles in the last few years because “some of the insecticides don’t always seem to work so well on them.” They’ve found that “all of the flea beetle insecticides in seed treatments work best under warm, dry conditions. It also appears that in most parts of the Prairies there’s been a shift from the black crucifier flea beetle to the striped flea beetle.”
Some seed treatments work better against specific types of flea beetle.
Hartley suggests that farmers monitor fields with yellow sticky tape in the areas where canola grew last year or is growing this season, to get a sense of which types of beetles are on your fields. This information won’t be helpful for 2016, but it could be helpful for selecting 2017 seed treatments.
The best place to put the yellow sticky tape is in between fields and near overwintering sites. You can do this in spring and even later in the year, like in August, to get a sense of what you are dealing with.
You’ll want to check the fields this fall to see where you’re noticing flea beetles; those may be the affected areas come springtime, after overwintering.