Grasshoppers
Controlling grasshoppers on pasture and rangeland can be costly.
Wyoming researchers have experimented with applying insecticide in 100-metre alternating bands across pastures, which cuts spraying costs in half.
Grasshoppers are mobile and often move between bands. If the insecticide has a residual effect that lasts a couple of days, the method can offer 80 percent or greater control, Gavloski said.
The bands can also help producers preserve natural predators of insect pests.
When controlling grasshoppers in grain crops, producers should remember that young hoppers are often most numerous early in the season on field edges and roadsides.
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They should scout field edges in late May and early June. If it’s found to be necessary, controls can be used before the grasshoppers begin spreading throughout the field.
That may save having to spray the entire field later on, Gavloski said.
Young grasshoppers are also more susceptible to insecticide, which means it might be possible to apply insecticide at a lower rate.
Sunflower beetles/seed weevils
Gavloski said spraying for sunflower beetles is economical when they cause about 25 percent or more defoliation on the upper eight to 12 leaves.
Some sunflower growers will spray early, when damage is well below 25 percent, if the larvae are numerous and it appears damage will eventually surpass 25 percent.
This may at times be the best choice, Gavloski said, but if other insect problems are a concern later in the season, such as seed weevils and banded sunflower moth, it may be better to delay spraying for sunflower beetles until damage is closer to 25 percent so that other insects can be controlled as well.
Gavloski said research is needed to determine the effectiveness and most ideal time for multi-insect spraying.
Seed weevils and banded sunflower moths usually move into sunflower fields as they are beginning to bloom, which in some years may be too late to spray for sunflower beetles. But in other years, it may be possible to delay spraying until then to get some control for all three insects.
While not always effective, targeting more than one pest with a single insecticide may help some farmers reduce insecticide costs with minimal reduction in control, said Gavloski.
Armyworms
True armyworms, which will feed on cereal crops as well as timothy hay, enjoyed a resurgence in eastern Manitoba last year.
Armyworms are most likely to flourish where there is a dense canopy.
“If you get some lodged grain, that’s where you’re more likely to find them in the highest numbers.”
Patch spraying is an option when armyworms are concentrated in areas of dense or lodged grain. Gavloski said the technique seemed to be successful in Manitoba last year.
“As far as I know, they didn’t have to go back and spray those fields a second time.”
However, he said patch spraying works only if armyworms are highly concentrated in specific areas of the field, which is not always the case.
Sufficient field scouting is needed to decide on the most economical control.
Patch spraying can also be used in fields where cutworms become a concern.
An area around the infected patch should also be sprayed to help prevent the cutworms from spreading.
Insecticide resistance
Gavloski emphasized the need to rotate families of chemicals, which reduces the risk of pest insects developing resistance to chemicals registered to control them.
Insecticide resistance is of greatest concern in crops where spraying is done year after year for the same nuisance insect, such as in potato crops affected by Colorado potato beetles.
Rotating between insecticides in the same chemical family is not considered resistance management, since the method of killing insects is often the same.
Gavloski also said heavy spraying increases the chances of infestations of secondary pests such as aphids, because the insecticides can eventually “knock out” beneficial insects like ladybugs, lacewings, and hover flies that control pests such as aphids.
Selecting insecticides less harmful to beneficial insects can reduce the risk of some insects increasing to levels where they are considered pests.
