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Here 's how to protect your cole crops from eight of America's least wanted.
If you've tried raising cabbage, broccoli, cauliflower, Brussels sprouts, mustard or kale, you've probably discovered that a host of insect pests share your enthusiasm for cole crops. Before you can take action to stop or reduce pest damage to your harvest, you first need to identify the specific pest that's sharing your supper. This guide will help you decide which cabbage vandal you're up against and what to do about it. (Crop rotation and garden clean-up are essential for controlling all cabbage pests.)
DESCRIPTION: Sometimes called "measuring worms" or "inchworms," the caterpillars are 1'/' inches long, light-green with whit lines along the sides of their bodies. When young, they may have a dark-brown head. Their marked looping motion while crawling helps to distinguish them from the cabbageworm. Adult moths have a l '&-inch wingspan, are mottled gray-brown, and fly at night near the ground.
RANGE: Throughout the United States and southern Canada.
LIFE CYCLE: Usually overwinter as a copper-colored pupa in a white, almost transparent, thinly woven cocoon attached to a plant leaf. Moths emerge around mid-June (earlier in warm areas). Each female lays about 300 greenish-white eggs, singly, on upper leaf surfaces. Eggs are dome-shaped and have ridges. Caterpillar stage lasts two to four weeks. Can have three or more generations per year in warm climates. DAMAGE: Newly hatched larvae eat small areas out of leaf undersides. As caterpillars grow, they move closer to the plant's center, eating large, ragged holes in leaves; eventually the plant may be entirely skeletonized. Caterpillars also may feed inward from leaf edges. The leaf surface is contaminated with greenish-brown excrement. These pests can be extremely destructive.
WHAT TO DO:
· Use pheromone traps to detect adult moths.
· Prevent egg-laying by covering plants with cheesecloth or a polyester row cover.
· Trichogramma wasps will parasitize eggs--try three releases of the wasps at two-week intervals, as needed.
· Spray or dust plants at regular intervals with Bacillus thuringiensis, according to directions, as soon as you see the tiny young caterpillars.
· If you have just à few plants, handpicking may be enough to control caterpillars.
· Plant early. Observe levels of looper activity, so that you can time future plantings to avoid peak populations.
· Clean up all cole-crop remains at the end of the season.
DESCRIPTION: Maggots are white, one-quarter-inch larvae that are pointed at one end. They feed on the surface of roots or tunnel into them. Adults are one-quarter-inch gray flies that resemble houseflies, but are smaller. RANGE: Primarily southern Canada and northern United States.
LIFE CYCLE: Adults emerge in spring and lay white eggs at the base of plants. Maggots emerge several days later; development and feeding continue for 20 to 30 days. Pupation occurs in the surrounding soil. After several weeks, a second generation of adults emerges to reseat the cycle. (Pupae overwinter in the soil.)
DAMAGE: Maggots feed on plant roots, causing lower leaves of cabbage, cauliflower and other brassicas to yellow. Plants may fail to grow, wilt or die.
WHAT TO DO:
· Start seedlings indoors. Cover plants with row covers for first four to six weeks after setting them out in the spring.
· Rotate brassicas annually.
· According to some studies, 3-inch disks made of tar paper or foam rubber could provide some protection if placed around the base of transplants when they are set out.
· Some beneficial nematode products are effective against maggots.
DESCRIPTION: These one-half-inch, grayish-yellow caterpillars have five purple-brown stripes and a black head. Small, adult moths are grayish and mottled with brown. When disturbed, they make short, uneven flights, landing on the ground or among plant leaves for camouflage.
RANGE: Primarily southern United States.
LIFE CYCLE: Gray-white eggs are laid singly in young plant buds or on mature plant leaf undersides. The caterpillars emerge in three days, and pupate in two weeks. Look for the webcovered cocoons on fallen leaves and soil debris. Moths emerge in a week.
DAMAGE: One webworm can ruin a plant. The larvae, feeding under a debris-covered protective web, tunnel into buds of young plants. Destruction of the original bud causes development of secondary buds that seldom
become firm heads by harvest time. The most serious injury occurs in late summer.
WHAT TO DO:
· Destroy webbed leaves with caterpillars inside.
· Eliminate weeds, especially pigweed . and lamb's-quarters, around the area ' as webworms often migrate from them onto cole crops. (Because of its protective web, the caterpillar is difficult to destroy with insecticides or natural enemies such as beneficial wasps.)
DESCRIPTION: These 11/4 inch, velvety-green, smooth caterpillars have dark stripes on their backs and broken yellow side stripes. They are slow crawlers and hide along leaf veins. The adult is a white butterfly with a 2-inch wingspan. RANGE: Throughout North America. LIFE CYCLE: Overwinters as pupa in gray or green rolled-leaf-shaped chrysalis with angular projections, suspended by silken threads from a plant or nearby object. The white butterflies have black spots; they are among the earliest seen in the spring. Females lay about 100 pale eggs singly on leaf undersides; eggs are laid upright on end and are fairly easy to detect. Caterpillars emerge in a week, with two to six generations per year. DAMAGE: Early forming outer leaves are riddled with irregular large holes of varying sizes. These caterpillars are more likely to eat through the smaller leaf veins than is the cabbage looper, and will feed closer to the plant's center. They can contaminate leaves with
dark-green excrement pellets. Because the caterpillars can devour seedlings overnight, you should begin treatment as soon as possible.
WHAT TO DO:
· Cover plants with cheesecloth or polyester row cover to prevent adult moths from laying eggs.
· Begin spraying Bt as soon as the eggs or small caterpillars are observed. Continue spraying once a week, and after rain, until all the butterflies are gone.
· For small plantings, handpicking may control caterpillars.
· Trichogramma wasps will parasitize their eggs: try mass releases at regular intervals.
· Natural control by viral and bacterial diseases and parasites can sometimes be effective
Clean up crop debris at the end of the season.
DESCRIPTION: Pale-green caterpillars are one-third-inch long. The larvae are easily disturbed and wriggle actively. If threatened, they drop from the leaf on a silken thread, then crawl back up later. Small, adult moths are brownish with diamond-shaped wing markings; they fly rapidly from plant to plant during the day.
RANGE: Throughout North America.
LIFE CYCLE: Caterpillars emerge from yellow or pale-green eggs laid singly on leaves. Each female moth deposits about 150 eggs. Life cycle is two to seven weeks, with up to six generations a year. Adult moths overwinter in cabbage debris.
DAMAGE: The larvae create multiple small holes around young plant buds, in the crevices between loose leaves and on leaf undersides. They may disfigure young plant buds so that heads will not develop properly.
WHAT TO DO:
· The same as for other cabbage caterpillars: Bt is very effective; destroy mustard-type weeds growing near cole crops.
DESCRIPTION: Sometimes called a "cabbage louse," the tiny (one-tenth inch) aphid is gray-green with a powdery waxy covering. It may be surrounded by sooty mold (growing on its honeydew excrement). It lives on leaf undersides in clusters.
RANGE: Throughout North America.
LIFE CYCLE: During most of the year, females are able to reproduce without males. From birth to reproductive size takes just six days. Males are produced in the fall only. Each female lays up to 100 eggs in the crevices on cabbage leaf undersides. They may reproduce year-round in warm climates. They overwinter as small black eggs on plant debris.
DAMAGE: They suck plant sap, which causes leaf cupping, curling and mottling. Young plants may be covered with aphid masses. Plants grow poorly and form small heads; seedlings can be killed. They may spread very destructive plant viruses.
WHAT TO DO:
· Release adult ladybugs and lacewing larvae, which are predators of aphids.
(Some species of hover-fly larvae, which already could be in your garden also eat cabbage aphids.) Encourage such beneficial insects by planting nectar-filled flowers nearby.
· Forceful sprays of water will knock aphids off plants, but spraying must be very thorough. For better results, spray with insecticidal soap. Spray as infrequently as possible; spraying too often could decrease yields. (Test the strength of the spray on a few leaves before spraying your entire crop.)
DESCRIPTION: Black ovoid weevil, one-eighth-inch long, has a curved, slender beak and six visible legs.
RANGE: Throughout North America
LIFE CYCLE: Adults hibernate in soil and emerge in spring. They insert small gray eggs into the plant stems (the area where they do so may show scarring). Whitish, one-quarter-inch long grubs emerge in a week and begin feeding within the stems and on leaf edges. Pupation occurs in round earthen cocoons just beneath the soil surface. The life cycle lasts about sever weeks; several generations per year are possible.
DAMAGE: Adults and grubs "mine" stalks and feed on leaves--usually early cabbage. Most often found in upper stem. Not a major problem unless there's a heavy infestation.
WHAT TO DO:
· Usually no controls are needed. If the curculio population was large last season, you should rotate your crop, then protect young plants with cheese cloth or a row cover
· Try sticky traps around the planting
to keep the beetles from traveling in or out. Destroy heavily infested rows.
DESCRIPTION: Shield-shaped red-orange and black flat beetle; three-eighths inch long, Has a disagreeable smell. Also called Calico bug, terrapin bug or fire bug.
RANGE: Southern United States. LIFE CYCLE: Adults overwinter around old cabbage plants and debris. Although it may appear intermittent!, during periods of warm weather, it generally emerges in early spring. Females lay white, barrel-shaped, black ringed eggs in rows on leaf undersides Young hatch in a week and feed for four to nine weeks before reaching full size. Expect about three generations per season.
DAMAGE: Can kill seedlings. Young nymphs suck plant sap, causing leaves to blotch, wilt, turn brown, then die. Entire crops can be destroyed, with the field looking like it's been swept by fire. Six bugs can destroy a small plant in a day.
WHAT TO DO:
· Remove nearby weeds and ground covers that could harbor harlequin bugs.
· If your planting is small, try handpicking the adults and eggs.
· If you use "trap crops," such as turnips or mustard greens, be sure to destroy harlequins quickly and thoroughly, or they will migrate to new hiding places.
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