Spears small. Causes: Young plants; low soil fertility; overharvested plants. Harvest lightly the first few years so plants can grow strong roots. Reduce harvest if established plantings begin to lose vigor. Asparagus is a heavy feeder; add lots of compost to maintain high soil fertility.
Spears small with brown streaks or gir- , died at soil line. Cause: Asparagus miners, j Larvae are Vis" long, white maggots. Adults are small black flies. Destroy infested spears to control.
Spears turn brown, may get soft or wither and dry. Cause: Cold injury. Cut and discard damaged spears. Cover spears with mulch or newspaper when freezing nights are predicted.
Spears small, with large lesions at or below soil line. Cause: Fusarium wilt. Leaves and stems yellow, plants wilt, seedlings die. There is no cure: remove and destroy infected plants. To avoid problems, don't put new plantings where asparagus or other Fusarium-susceptible plants have grown in 8 years. Plant disease-free seed and crowns or resistant cultivars such as 'Greenwich', 'Jersey Giant', 'Martha Washington', and 'Viking KB3'. Disinfect seed before planting. Soak it for 2 minutes in a 10 percent bleach solution (1 part bleach to 9 parts water), and rinse for 1 minute under running water.
There are reports that adding rock salt to asparagus soil at 2 pounds per 100 square feet may suppress Fusarium infection and improve asparagus root growth.
Spears turn brown near soil line. Cause: Crown rot. Remove and destroy diseased plants, including roots. Prevent crown rot by planting in raised beds and maintaining good drainage. Keep soil pH above 6.0. Wait 2 years before harvesting new plantings. Some research suggests that not harvesting the first spear of the spring on each plant may help prevent crown rot because the developing frond produces food for the plant.
Spears crooked and deformed, may be brown, or scarred; leaves chewed or missing. Causes: Asparagus beetles; asparagus fern caterpillars; cucumber beetles; mechanical injury. Asparagus beetles are blue-black, '/*" long insects with cream-colored spots and red borders on wing covers. Larvae are '/>" long, humpbacked, gray grubs with black heads. They are most active in cool weather. Spotted asparagus beetles are reddish orange with 12 black spots on wing covers. Larvae are orange. Fertilize plants to encourage new leaf growth. Apply a commercial pyrethrin spray or dust to control beetles. Destroy tops in late winter to remove overwintering beetles and future problems.
Asparagus fern caterpillar (also known as the beet armyworm) feeds on leaves. It is a dull green. Vh" long caterpillar with a light-colored stripe along each side of the body. Handpick or spray with BTK to control.
Cucumber beetles also eat asparagus leaves. For description and controls, see "Leaves with chewed holes" on page 215.
Deep cultivation can damage developing spears. Cultivate shallowly or use mulch instead. In windy areas, blowing sand can scar spears; protect plantings with windbreaks.
Spears chewed at soil line. Cause: Cutworms. Check for cutworms at night with a flashlight. Control with BTK or parasitic nematodes. See "Seedlings clipped off at soil line" on page 246 for more controls.
Spear bracts open prematurely (feathering).
Cause: Excessive heat. Harvest spears daily when they are about 8" high, especially when temperatures are above 95°E
Leaves yellow; growth slow. Causes: Nitrogen deficiency; waterlogged soil. Spray foliage with fish-meal tea and side-dress with compost to correct nitrogen deficiency. Waterlogged soil will produce the same symptoms. Make sure soil is well-drained or plant in raised beds.
Leaves yellow; plant dwarfed or rosetted. Cause: Asparagus aphids. These soft-bodied, pale green, powdery-looking insects suck plant juices and cause plants to weaken. Knock aphids off plants with a strong blast of water, or spray with insecticidal soap. If that fails to control the problem, apply a commercial pyre-thrin spray or dust.
Leaves turn brown and drop; stems and branches have small reddish blisters. Cause: Rust. Clean up and dispose of tops in late winter to eliminate overwintering spores. Rust weakens plants by reducing the leaf area and the amount of food stored in the roots. Repeated attacks can kill plants. Plant resistant cultivars such as 'California 500', 'Jersey Giant', 'Martha Washington', 'Mary Washington', 'Rutgers Beacon', 'Viking KB3\ and 'Waltham Washington'.
Leaves dull gray-green to brown. Cause: Thrips. Adults are tiny, pale, rapidly moving, winged insects. The larvae are smaller, wingless versions barely visible with the naked eye. Trap thrips with sticky traps or spray with insecticidal soap. Research indicates that blue and yellow sticky traps are the most effective thrips catchers in greenhouses. Other studies suggest that thrips are most attracted to white sticky traps outdoors. Hang traps slightly higher than the tops of the plants.
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