Vegetable Crop Update - Sweet Corn, Beans and Pea Edition
by Elaine Roddy, Vegetable Crop Specialist (elaine.roddy@ontario.ca)

European Corn Borer - Accumulated Growing Degree Days
Corn Earworm

European Corn Borer - Accumulated Growing Degree Days

Univoltine corn borer adult populations peak at 650-700 GDD.  Growers in the Hamilton, Waterloo, Peterborough and Ottawa areas will be experiencing peak flights and egg-laying at this time.  

The second generation of bivoltine European Corn Borer adults usually emerge at 700 GDD.  The population peaks at 1050-1100 GDD.  Growers in Southwestern Ontario can expect to see increased corn borer activity over the next few weeks.

European corn borers controls are most effective when targeted at the very young larvae.  Monitor fields regularly for egg masses and signs of windowpane or pin-hole feeding.  Apply insecticides at the first sign of activity in the field.  The spray threshold for this pest is 5% of the plants with either egg masses or feeding damage.

Figure 1, Windowpane Feeding

Figure 2, European Corn Borer Eggs

Corn Earworm

Researchers in the Southern United States have been reporting very high levels of corn earworm activity.  The current weather forecasts indicate that there is a moderate risk of these populations moving into the mid-western states over the next 3-5 days.  Ontario is at the edge of the predicted flight zone; however growers should be aware of the potential for increased activity over the next few weeks.

Corn earworm must be controlled before they enter the protection of the husk.  Insecticide applications made on freshly silking corn will help to control this pest as it hatches.  A high level of pyrethroid resistance has been documented in the corn earworm population across North America.  Coragen insecticide is an effective alternative to the commonly used pyrethroid sprays.