Manitoba pest survey results are in
Cutworms, grasshoppers, flea beetles and bertha armyworm are all on top of the watch list for 2019, as numbers were higher in 2018. All four overwinter well in Manitoba provided there’s enough insulation for them.
Cutworm populations were still a concern in some areas of Manitoba in 2018. According to the Manitoba Agriculture report compiled by entomologist John Gavloski, cutworms were a concern in canola, oats and corn, but not in soybeans. Redbacked and dingy cutworms appeared to be the main species causing damage, and resulted in some reseeding in oats and some reseeding in canola. In corn, there were isolated incidents where cutworm levels were high and insecticides were applied.
Grasshoppers are also on the watch list for 2019. Levels were high in 2018, and since grasshoppers like to lay eggs in late summer in areas where there is green vegetation, there could be high populations in ditches and along field edges. Often those are areas, even in drier winters, where a lot of snow accumulates, said Gavloski. Grasshoppers don’t like a lot of rain in June, as that’s right when they’re beginning to hatch, so watch the forecast around this time. “Going into next year, grasshopper populations have been building,” said Gavloski. “And if the trend continues then there certainly could be some grasshopper issues in some areas.” MAFRI’s grasshopper prediction map is posted on its website. A lot of the map shows low to moderate risk, but there are a few areas of higher risk. “In context, the map has higher grasshopper levels on it than the previous year, so the trends are what’s important,” he said. “Populations are building.”
3. Flea beetles
Flea beetles, on the other hand, seem to be a chronic problem in Manitoba. They don’t seem to be well regulated by adverse weather or natural enemies. And the species that are the main pests are cruciferous specialists, so they feed heavily on canola. “For them, there’s a super abundance of food on the Canadian Prairies,” said Gavloski. Not only do they not suffer from resource shortage, but they’re also decent enough fliers that if they run out, they can easily get themselves to a nearby field. Populations will drop slightly, said Gavloski, but flea beetles don’t seem to suffer the deep swings that insect pests like bertha armyworm do. While flea beetles only have one generation per year, adult generations surface twice because they overwinter as adults. The first adults emerge in late summer, and then the same adults will cause damage the following spring. “That late-summer population, they will feed on canola as well, but the plants at that time are big and have pods,” said Gavloski. “Some growers get really worried that the flea beetles will feed on the pods, the pods will split open and they will lose seeds.” While the worry is justified, research doesn’t show great yield losses due to pod shatter. “Even at hundreds of flea beetles per plant, they weren’t getting the big yield losses,” said Gavloski.
4. Bertha armyworm
Bertha armyworm levels were also high in 2018, especially in the western part of Manitoba. All of the higher populations and insecticide applications occurred in the southwest and northwest regions, and the western part of the central region. A few thousand acres were reported to have been sprayed in the northwest. No higher populations of bertha armyworm were reported from eastern Manitoba. Pheromone-baited traps were set up at 99 locations in Manitoba in 2018 to monitor the movement of adult moths between June 3 and July 28. Of those, 85 of the 99 traps were in the low-risk category, while 13 were in the ‘uncertain’-risk category. One trap in the southwest was in the moderate-risk category, which means a 900 to 1,200 cumulative moth count.
5. Diamondback moth
As a final note, Gavloski added diamondback moth to the list as a pest to watch. Diamondback moth populations can vary greatly from year to year, making them difficult to predict. Manitoba Agriculture will be monitoring for the pest throughout the growing season. “The main thing with diamondback moth is how to scout and how to make good decisions, that’s the tricky part,” said Gavloski. The economic threshold for diamondback moth is based on the number of larvae per square foot, which requires knocking larvae off plants. Growers are often alarmed when high numbers of diamondback moth larvae appear in their sweep nets during a scouting mission. The knee-jerk reaction is to spray. “But one thing I like to remind them of is when you’re using a sweep net, every sweep goes through a lot of plants,” said Gavloski. “When you do a set of ten sweeps, you’ve covered quite a few plants. To get 20 to 30 larva in 10 sweeps, you could still realistically be well below the economic threshold, which is 20 to 30 larva in a square foot of plants.”