Corn Rootworm

Western and northern corn rootworms are able to overwinter across all of the corn-growing region, so their development is chiefly driven by accumulated four inch depth soil temperatures where eggs are laid during the previous growing season.  Fields primarily growing continuous corn are at the greatest risk of experiencing western or northern corn rootworm damage.  Once enough soil heat units have accumulated, larvae hatch and begin feeding on corn roots (if present).  Soils that are extremely wet or those that are more abrasive (in addition to not having any corn roots present at the same time as hatch) can limit corn rootworm development and subsequent damage.  Therefore, soils that are drier and warm more quickly in the spring stand the greatest risk of seeing increased corn rootworm numbers and earlier in the season (such as in 2012).  Later in the summer, pupation and adult emergence occurs, and a secondary threat to corn (in addition to other plants such as soybeans and alfalfa) occurs during silking.  Corn rootworm adults can clip silks and reduce pollen levels that may lead to poor pollination.  Migration events are primarily focused locally but can be intense especially between fields that show differing growth stages.  Scouting, in addition to following forecasts, provide the best method for managing this particular insect.

Source:  University of Illinois Integrated Pest Management

http://ipm.illinois.edu/fieldcrops/insects/corn_rootworm/factsheet.html

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 development is driven primarily by air temperature heat unit accumulation as this insect can overwinter successfully across the corn-growing region.  In a typical year, western bean cutworm emergence is first observed in the Plains and western Midwest where heat units accumulate more rapidly.  Emergence and subsequent flights then spread east and northeast into the upper Mississippi River valley, Great Lakes region, and southern/southeast Canada as heat unit accumulations increase in fields in these regions.  Migrations can occur especially during peak flight and when primarily strong west to east wind events occur following cold frontal passages.  This particular insect, once only a threat to the Plains states, has now become a widespread nuisance in fields across much of the Midwest, Great Lakes region, southern and southeastern Canada, and portions of the northeastern United States as it has greatly expanded its range in the last decade.

Source:  University of Illinois Integrated Pest Management

http://ipm.illinois.edu/vegetables/insects/western_bean_cutworm/