By Bonnie Ennis, Colorado State University Cooperative Extension Agent, Horticulture
Several insects are common in area vegetable gardens, but organic gardeners can control these pests with a combination of cultural practices.
These controls do not offer the quick fix, "spray and kill" effect of common garden insecticides. Unlike such chemicals, however, the following organic insect pest controls are not toxic to humans, pets or the environment.
The corn earworm feeds on corn eartips, causing chewing damage and the irritating presence of larvae and droppings.
CONTROLS: Apply a one-time drop of mineral oil to corn ear tips when the silks begin to turn brown. If the eggs and larvae survive this barrier, use a knife to cut off affected eartips before cooking. Most of the remaining ear will be clean and very edible.
Imported Cabbage Worm
These green, worm-like larvae chew on broccoli and cabbage leaves. They also feed inside cracks and crannies of broccoli florets and tunnel into cabbage heads.
CONTROLS: After eggs hatch, but before they hide inside their hosts, handpick or wash off larvae with a heavy spray of water.
Try early spring plantings when cabbage worm populations are low. (They increase throughout the season.) 'Bacillus thurengiensis,' a bacteria applied before the worms go into hiding, provides good control against this pest. Consider planting red cabbage varieties, which appear to be more resistant to this pest than green cabbages. Use row covers to prevent adult moths from laying eggs. Cover ends with cheesecloth to encourage air movement and to prevent high temperature beneath the covers.
The tiny leafminer tunnels through older spinach leaves, beets and swiss chard.
CONTROLS: Very early spring and fall plantings will stop most infestations. For an extra early spring crop, plant spinach in September to overwinter and produce in late March or April. Inspect leaves and crush egg masses. Pick and destroy infested leaves. Floating row covers, used on soil not previously infested, can exclude adult flies who would lay eggs. Cover row cover ends with cheesecloth.
Western Cabbage Flea Beetle
Small adult beetles cause shot-hole chewing wounds. Affected are plants from the Brassica family (Chinese cabbage, broccoli, Brussels sprouts, cabbage, cauliflower, rutabaga, mustard, turnip, kale, collards), beets and lettuce. Seedings are most susceptible, although later generations can damage leafy vegetables prior to harvest, especially Chinese cabbage.
CONTROLS: Plant more seeds than you will need. Assume some seedlings will survive to provide a good crop. Hasten crops beyond the seedling stage by planting in a well-prepared bed, tilled with added organic matter. Assess the success of previous crops to determine the soil's fertility. Remove plant debris in winter, as adult beetles overwinter in these materials. Floating row covers can exclude beetles while seedlings are being established.
Cabbage and Turnip Aphids
These two aphids often appear side by side on Brassica family crops. As with other aphids, cabbage and turnip aphids suck sap from leaves and often distort and kill new growth. They often blend with green vegetables and sometimes survive washing to appear in the salad bowl.
CONTROL: Spray liquid soap, three tablespoons per gallon of water. Repeat every three to four days to keep poulations acceptably low. Wash treated vegetables before eating. Till overwintering plants into soil to reduce winter aphid survival.
Most problems with this pest occur when its natural enemies, ladybird beetles, syrphid flies and parasitic wasps, have been destroyed.
CONTROLS: Hose plants with a strong jet of water to kill and dislodge many of these aphids. Soap sprays (three tablespoons per gallon of water) also are effective.
Photograph courtesy of Lynne Conroy.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010