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.
WBC DEVELOPMENT FAVOURED IN SANDY SOIL TYPES
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.
TANK MIX INSECTICIDES FOR BEST RESULTS
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.
ROTATE CORN WITH NON-HOST CROPS
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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