Exactly which insect pests will chomp their way into your crops this year and how much damage they’ll do depends on wind, weather and, above all, your scouting and management choices. This year, Saskatchewan growers should keep an eye out for rising populations of two-stripe grasshopper and wheat midge, meanwhile dry spring conditions will increase flea beetle pressure and bertha armyworm remains a wild card.
Two-stripe grasshopper populations appear to be on the rise, says James Tansey, Saskatchewan Agriculture’s provincial insect and vertebrate pest specialist. Last year’s counts showed populations in excess of 10 per square metre in southeastern Saskatchewan, with highs near Kindersley in excess of 20 per square metre. Lentils and flax are particularly sensitive to damage.
“If we end up with dry conditions in the spring, there’ll be the potential for heavy grasshopper populations regionally,” says Tansey.
June control of field edges, especially those bordered by lush ditches and other prime grasshopper egg-laying areas can make a fundamental difference in later-season grasshopper damage. Control should only be undertaken if the numbers warrant it.
Wheat midge numbers are also growing, with high populations noted last year in the north-central and west-central growing regions. Expect wheat midge issues in those regions again if 25 millimetres of rain falls before the end of May.
“Producers who have had wheat midge damage in the past should be considering varietal blend choices, and producers should be on the lookout this year,” says Tansey.
Pea leaf weevil and cabbage seedpod weevil
It’s not all bad news on the insect front, however. Pea leaf weevil and cabbage seedpod weevil populations were down significantly province-wide last year. In fact, says Tansey, “We were having trouble finding pea leaf weevil damage at all in 2019.”
Agriculture and Agri-Food Canada (AAFC) researchers are currently studying what factors could be contributing to the population decline. Tansey suspects two key weather factors likely played in producers’ favour last year: deep cold snaps with little snow cover in the 2017-18 and 2018-19 winters, together with dry conditions through the early growing season. Since both of these weather factors appear to be increasing in frequency, producers can hope pea leaf and cabbage seedpod weevils may be less notable pests in the future.
While numbers are down in both pea leaf and cabbage seedpod weevils, Tansey cautions producers to remain vigilant. “Despite lower levels, both those insects are invasive and spreading north and east.”
Whereas dry spring conditions may be depressing weevil numbers, flea beetle populations are being supported.
“If we have another dry spring like we have for the last few, I do anticipate big flea beetle pressures,” says Tansey. “Flea beetles are a big question because they can do so much damage so quickly.”
Bertha army worm
Bertha army worm populations vary significantly from year to year. Last year’s surveys showed lower numbers than the year previous, but that decline will not necessarily impact this year’s numbers.
“Bertha army worm are a cyclical pest. Last year was low but we don’t know what factors contributed to that. There’s just no way of accurately telling what the population will look like this year,” says Tansey. “We’ll be monitoring and posting on that. I recommend producers keep an eye on our surveys.”
Pea aphid numbers were relatively high in lentils last year. Tansey reports that Saskatchewan Agriculture has a study planned in collaboration with AAFC for this coming growing season on the timing of seeding and spraying for pea aphid control, as researchers are still uncertain about best management practices. The good news, however, is that not all pea aphid control has to come from producers.
“Natural enemies can have a profound effect on pea aphids,” says Tansey. “Producers want to do all they can to support beneficials in their fields.”