Western bean cutworm (WBC) is a relatively new pest in Eastern Canada that can reduce the yield potential and grain quality of corn. Initially an issue near Bothwell, Ont. in 2008, this late-season pest has spread throughout cornfields in southern Ontario and is now also found in southern Quebec. WBC has also been found in dry beans in Western Canada, but it has not yet had the same impact there.




Unlike many other cutworms, WBC do not cut plant stems, instead, they feed on the reproductive parts of corn plants. Besides migrating in, the larvae can overwinter in the soil, and sandy soils are ideal for WBC because it’s easier for the larvae to burrow into. The higher prevalence of no-till farming, combined with milder winters in Ontario in recent years, may also be helping WBC overwinter, thereby contributing to the pest’s spread.


In Eastern Canada, WBC began emerging from the soil as adult moths around the start of summer. Typically, a peak flight period occurs in mid to late July that coincides with the tasseling stage of the corn crop. Shortly afterwards, the eggs laid by the moths will hatch and start feeding on the pollen before moving down to the ear to feed on silks and eventually the grain. The damage caused by feeding can act as infection sites for diseases that further degrade the quality of the crop.




Corn producers in Eastern Canada are primarily tackling WBC by applying insecticides with an effective mode of action against the pest. Growers can choose between several insecticide products labeled for WBC larvae control, and the preferred application method is in-season foliar spraying. Best management practice is to tank mix insecticides with multiple modes of action to maximize the effectiveness of their pesticide program and reduce the risk of developing resistance.


The action threshold for insecticide application is when five per cent of scouted plants have at least one egg mass. Scouting is crucial for your spray timing, since insecticides are ineffective once WBC larvae enter the corn ear. Ideal application timing is when the majority of the eggs have hatched, but before the larvae move into the ear. If the eggs have not hatched and the plants have tasseled, application should be applied when most of the eggs are expected to hatch.




If WBC is a concern in your area, rotating corn with non-host crops like soybeans and winter wheat can help prevent the pest from showing up in your fields. Growers can also consider planting their corn a little earlier. This means tasseling will happen earlier as well, giving growers a better chance of avoiding the peak period in summer when the majority of WBC moths are laying their eggs in the corn crop.


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