Department of Entomology
Entomological Notes

The 2000 season was cool, which tends to slow insect populations, but there was plenty of insect management activity. For example, the web site mapping sweet corn pests was accessed close to 2000 times, and we will continue to operate it until Sept. 15. However, as the end of the field season approaches, its worth considering what practices during the fall and winter will help manage insects for next season.

Crop rotation is always a valuable cultural management technique for both insects and diseases. Sweet corn is a straight forward example. Corn rootworm adults lay eggs at the base of corn, and these eggs overwinter. Next spring, the hatching larvae need to find corn roots, and they can only move about 3 to 5 feet to search for corn roots. Even a short distance rotation, to an adjacent field, effectively prevents the build up of corn rootworms. In fact, rotation is more effective at controlling rootworms than any soil insecticide applied at planting. Disking or plowing corn crop residues and maintaining good weed control to eliminate overwintering sites can also reduce flea beetle and sap beetle populations.

Crop rotation can also help in crucifers. Diamondback moth has started to overwinter in a few spots in Pennsylvania over the last two winters, and crop destruction reduces overwintering. It also helps slow the build up of flea beetles in crucifer crops.

Rotation also helps to control Colorado potato beetle in tomatoes, potatoes and eggplant. These beetles overwinter as adults in both field edges, and in the fields themselves. Rotation distance has a strong effect on the degree of control. Research has shown that a 0.2 to 0.6-mile distance was required to reduce beetle densities by 50% compared to non-rotated fields. But even a short distance will help - the degree of help will increase with distance out to about a half mile. Rotation for potatoes is also important for white grub control: potatoes should not follow grass fields, especially in years of heavy beetle flight.

Cleaning the pumpkins out of your field may also help with cucumber beetles on your farm. The literature claims the striped cucumber beetle overwinter at the edges of fields, under leaves and debris. While this may be true, we also discovered the beetles burying into pumpkins and the soil immediately under pumpkins that were left rotting in the field. I believe that some (I don't know what percent) of the beetles moved from other cucurbits that matured earlier (cucumbers and melons) to the late-season pumpkins, and then overwintered under these rotting pumpkins. Destruction of cucurbit crop residues also reduces overwintering sites of squash bugs. And for squash vine borer, North Carolina reports help from fall disking to expose cocoons, followed by deep spring plowing.

Winter cover crops are important for soil management. If you are planting into those crops in the spring, get the residue incorporated about a month prior to planting to reduce problems from seedcorn maggots in beans, cucurbits, and sweet corn. These maggots are the larvae of a small fly that lays eggs in the spring near the base of new transplants or germinating seeds. The fly has a preference for areas with higher organic matter. So rotting vegetation for a freshly tilled field will be more attractive to the fly. The same logic holds if you are applying manure to that field - stop applying and get the existing manure incorporated at least a month before planting. Other horticultural practices in the spring that encourage rapid plant emergence and growth of the seedling can significantly help. These include avoiding planting in cold soils, and shallow planting in a well-prepared seedbed.

In summary, crop clean-up and rotation is a good cultural practice for most vegetable crops. Winter cover crops help create the clean environment because the vegetable crop residues are removed, and also help with soil management, but remember to get those winter cover crops incorporated well before you plant into them to avoid maggot problems.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

Authored by: Shelby Fleischer, Professor

February 2002

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Where trade names are used, no discrimination is intended and no endorsement by The Pennsylvania State University or Pennsylvania Department of Agriculture is implied.

Entomological Notes are intended to serve as a quick reference guide and should not be used as a substitute for product label information. Although every attempt is made to produce Entomological Notes that are complete, timely, and accurate, the pesticide user bears the responsibility of consulting the pesticide label and adhering to those directions.

Issued in furtherance of Cooperative Extension Works, Acts of Congress May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture and the Pennsylvania Legislature. D. Jackson, Director of Cooperative Extension, The Pennsylvania State University.

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