Corn Earworm

Accurately forecasting Corn Earworm migration is possible. It involves the daily monitoring of insect traps throughout the country and is based on the hypothesis that increases in insect trap counts correspond with increased migration risks. Weather is a critical factor in determining if the migration may or may not occur—with some uncertainty, summer weather patterns can be predicted in advance of occurrence. When a southern source region of Corn Earworm is present, insects may migrate northwards based on a number of factors:

• Climatology (crop stage and generational aspects)
• Strong nighttime low level jet stream
• High and low pressure cells creating an “insect pump” effect
• Precipitation or downward moving air serving as a “drop zone”

Source: Vegetable Insect Management, Chapter 1A (How Weather and Climate Impact Your Pest Management Decisions), pages 23-29. Authors: Mike Sandstrom (lead), co-authors David Changnon, Brian R. Flood. Image is on page 26 and was created by Tracy Flood.

Western Bean Cutworm

Western Bean Cutworm migration is driven much more by heat unit accumulation, as these insects can survive winters in the Corn Belt. The greatest migration risk comes when the Kansas/Nebraska source regions become active and a good west to southwest wind event occurs. This also puts Iowa/Illinois at risk from both local heat unit development populations and migration events.