Williams County Western Bean Cutworm Monitoring Update – Week #5: Time to Scout for Egg Masses!

For the fifth week of Western Bean Cutworm (WBC) monitoring (July 16 – 22) seven moths per trap were observed which means it is time to scout for egg masses in corn fields that are pre-tassel or approaching tassel.

Here is how to scout for WBC and treatment recommendations (provided by Amy Raudenbush):

  1. Randomly choose at least 20 consecutive plants in 5 locations within a field (a total of 100 plants per field).
  2. Inspect 3–4 leaves on the uppermost portion of the corn plant. It is very useful to look at leaves with the sun behind them – often the shadow of the egg mass will reveal it without having to examine the leaf closely. 

Field corn should be treated with a foliar treatment if more than 5 % of inspected plants have eggs or larvae. Sweet corn should be treated if more than 4 % of inspected plants have eggs or larvae (processing market), or 1 % of plants (fresh-market).

If the number of egg masses/larvae exceed the threshold (mentioned above), foliar applications of insecticides are available, especially those containing a pyrethroid. Timing an insecticide application is critical and must happen before the caterpillar enters the ear, but after the eggs hatch (Figure 3). If the eggs have hatched, applications should be made after 95% of the field has tassels. If the eggs have not hatched, monitor the egg masses for the color change. Newly laid egg masses will be white but turn purple as they mature. Hatch will occur within 24–48 hours once eggs turn purple.

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Figure 3. Western bean cutworm egg mass starting to hatch. Larvae are visible briefly after hatching, before they enter the corn ear. Photo by: Amy Raudenbush, Ohio State University.


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