By Carl Wilson, Cooperative Extension Agent, Denver County
The value of floating row covers for spring and fall frost protection plus summer shading and cooling makes them a wise addition to your vegetable garden supplies. Yet, how do insects react to these wispy thin sheets of material thrown over plants?
The best way to think about managing insects under row covers is to examine which insects are trapped and which are excluded. Row covers can keep troublesome pests of spring vegetables, such as spinach leafminer, from damaging the leaves. Other early pests that can be screened out include aphid, leafhopper, cabbageworm, and cabbage looper.
Summer pest protection is offered against squash bug, cucumber beetle, bean beetle, corn earworm, grasshopper and whitefly.
If a pest does sneak under the cover and multiply, the cover also will screen out natural insect enemies such as lacewings and ladybird beetles. In this situation, you might need to remove the cover to allow predator insects access. Or you also might resort to spray.
The insects mentioned above spend the winter outside the garden. Insects that overwinter in garden soil near the previous host are a different story. When these insects emerge from their winter slumber to find their favorite plant food handy and a screen that protects them from insect enemies, these pests can be real problems. Vegetable root maggots, such as those affecting onions, corn and beans, are examples of pests that could get out of control if floating row covers complicate natural insect movement.
The answer to this dilemma is to rotate vegetables to a new location in the garden every year. This way, insect pests emerge from the soil to find themselves close but yet screened away from their food by the floating row cover.
Knowing how insects overwinter is invaluable in heading off possible problems from vegetable insect pests when using floating row covers.
HOW INSECTS OVERWINTER IN THE GARDEN
Onion and seedcorn maggot
Colorado potato beetle
Asparagus aphid (difficult to rotate the host plant)
Flea beetle (this pest affects many vegetable seedlings)
(These insects have the most potential for causing plant damage under row covers)
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010