Gardening Articles: Edibles :: Vegetables
Cole Crop Diseases and Pests (page 2 of 2)
by National Gardening Association Editors
Small, sap-sucking insect often found on undersides of leaves. May introduce fungal bacterial and viral diseases. Leaves of infected plants will crinkle and growth will be stunted. Remove and destroy parts of leaves where colonies occur. Spray with insecticidal soap.
Small, whitish larva of a black fly. Bores into stems and roots, causing plants to wilt and die. Cover transplants with cheesecloth or a floating row cover to prevent flies from laying eggs in surrounding soil. Alternately, place a flat, 4-inch-diameter tar-paper collar with a slit in it for the plant stem around the transplant on the ground. This will discourage adult flies from laying eggs.
Pale green worm that crawls in distinctive looping or "measuring" movements. Feeds on undersides of leaves; breeds two or more generations each season. Pick off or spray with Bt in the late afternoon.
Larva of white cabbage butterfly. Green, with light and dark stripes, about 11/2- inches long. Eats very large holes in leaves; bores into cabbage heads. Handpick worms (locate from brown-black droppings on lower leaves). Some people have luck sprinkling worms with small amounts of salt, wood ashes or diatomaceous earth. Spray with Bt weekly in the late afternoon as new eggs hatch. Use floating row covers to prevent adult white butterflies from laying eggs.
Fat larva of dull-colored, medium-sized moths. Can feed underground, on the surface, or above ground, but does most damage by chewing through young plant stems at ground level. Use cutworm collars at transplant time.
Black, shield-shaped adults with bright red markings hatch from barrel-shaped eggs. Nymphs may kill young plants by sucking out sap. Handpick bugs and destroy egg masses regularly. Spray with pyrethrum for severe infestations.
Black, brown or striped jumping beetle, about 1/16 inch long. Attacks young plants by chewing leaves so they look as though they've been shot full of holes. Spray with pyrethrum.
Note: One easily practiced preventive measure against many of the insects attacking cole crops is sanitation. Be sure to till in or cull and destroy plants that have been bothered by imported cabbageworms, cabbage loopers or harlequin bugs. To survive, these pests must overwinter on some plant part, such as leaves or stems. Depriving them of a home during the cold months will reduce their numbers in your garden the following season.
A Note on Bt
Bacillus thuringiensis (Bt), the biological insecticide sold as Dipel or Thuricide, is extremely effective against worms and caterpillars. It has the added advantage of being harmless to all other forms of life, including humans.
Bt works because it contains a bacterium that only infects moth larvae -- cabbageworms, cabbage loopers, cutworms, even the large tomato hornworms that strike just when your tomatoes are prime for picking. Don't worry about Bt and our gardening friends, earthworms. They're not moth larvae, so they cannot be affected.
You generally mix Bt with water and spray it on your crops. The best time to use it is when you first see the white cabbage butterflies around the garden. If you spray your plants in late afternoon every 7 to 10 days, you shouldn't be bothered by worms in your garden.
If you have a small garden, or you don't own any spray equipment, you can apply Bt with an ordinary houseplant mister. Just rinse it thoroughly when you're finished.
As with any spray, read and follow the directions that accompany Bt. Practice the other preventive measures outlined elsewhere in this book and enjoy a fine harvest!