Cole Crop Diseases and Pests
by National Gardening Association Editors
Disease and insects can cause problems for your cole crops. Here's a list of the most common ones to look out for, and some ideas for control.
Lifeless, yellowish green color appears in plant (especially cabbage) two to four weeks after transplanting. Caused by a fungus that lives in the soil indefinitely. Especially troublesome in wet areas during hot weather. Use resistant varieties (indicated on the seed packet by the initials "YR"), plant on raised beds if drainage is a problem and rotate crop every year.
Caused by a fungus, this disease infects young plants, causing them to wilt because it rots away the stems. As the disease progresses, dark, sunken areas develop on the stems. Disease spreads in humid, rainy weather. Crop rotation and good garden sanitation are the best prevention.
A bacteria that can invade plants at any stage, blackening veins and affecting head formation. In severe cases, no head will form, or the existing head will rot. Rotate crops and remove plant debris. Cabbage and cauliflower are more susceptible than are broccoli or Brussels sprouts.
Swelling of roots caused by a slime mold that lives in the soil. Crop rotation is the best remedy and prevention. This disease doesn't thrive in alkaline soil, so adding lime to acid soils to raise the pH above 7.2 may help.
Primarily a southern disease caused by nematodes. Knots form on smaller roots and nearer the tips than clubroot. Crop rotation can help somewhat, and in sunny, warm parts of the country a technique called soil solarization also works well. Check with your county extension agent for control techniques appropriate for your area.
Some diseases, including several bacteria and fungus-caused wilts, cannot really be checked once they appear. Other diseases may be slowed by applying a fine sulfur dust or other organic fungicide to the plants. The best way to avoid diseases in the cabbage family, and in all your vegetables, is to stop trouble before it hits.
Keeping Bugs Out
Insects seem to plague spring-planted cole crops more than some other vegetables. This isn't because bugs would rather chew on broccoli than beans. It's partly because many insect populations emerge -- hungry -- early in the season. Often, your cole crops are the only food in sight. Also, the distinctive odor of cabbage-family vegetables may make them especially easy prey for insects.
One way to cut down on insect problems is to depend largely on the fall garden for your supply of cole crops. Insect populations are generally past their peak by the end of the summer, and increasingly cool temperatures discourage those that remain. You can also encourage insect-eating birds such as martins by providing a bird house in the garden.
Learn to recognize harmful insects (listed below), and make daily visits to your garden to pick off or destroy any unwanted pests before they ruin large amounts of your crops.
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!
|To Spray or Not to Spray||Table of Contents|