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Problem Solver Plant Marquee

Plant:

Lettuce
Image of Lettuce
Adaptation
Throughout the United States.
Planting Method
Sow seeds 1/4 inch deep. Thin seedlings or set transplants 4 to 6 inches apart. For a continuous harvest, plant some seeds or plants every 2 weeks.
Soil
Garden soil that''s rich in organic material.
Water
Apply enough water to keep the soil moist but not wet. Do not allow the soil to dry out.
Planting
In cool-summer regions, you can grow lettuce all summer and into fall. In areas where winters are mild, you can grow it into the fall and winter. Where both summers and winters are mild, you can grow lettuce year-round.
Fertilizer
At planting time, add a continuous-release plant food formulated for vegetables.
Harvest
Cut plants with a sharp knife in the early morning. Head types: Head should be full and firm. Cut just above the soil line. Looseleaf types: The entire plant may be cut when it''s the size of your hand, or pick the outer leaves as you need them. Leave a few center leaves for future picking.
Related problems

Aphids - Lettuce

Image of Aphids - Lettuce
Aphids

Aster Leafhopper -

Image of Aster Leafhopper
Aster Leafhopper

Cabbage Looper -

Image of Cabbage Looper
Cabbage Looper

Cutworms - Lettuce

Image of Cutworms - Lettuce
Cutworms

Downy Mildew - Lettuce

Image of Downy Mildew - Lettuce
Downy Mildew

Mosaic Virus - Lettuce

Image of Mosaic Virus - Lettuce
Mosaic Virus
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Aphids - Lettuce

Image of Aphids - Lettuce
Aphids
Description
Leaves turn yellow and may be distorted, curled, and puckered. Pale green, yellow, or purple insects cluster on the undersides of leaves.
Analysis

Aphids do little damage in small numbers. They are extremely prolific, however, and populations can rapidly build up to damaging numbers during the growing season. Damage occurs when aphids suck the juices from lettuce leaves. The green peach aphid (Myzus persicae) may also spread lettuce mosaic virus, a disease that dwarfs lettuce plants, rendering them unproductive. The green peach aphid is pale green with three dark lines on the back. Its shiny black eggs spend the winter on the bark of fruit trees. About the time peach trees bloom, the eggs hatch and the young aphids begin feeding, first on the tree; then they migrate to vegetable and flower plants.

Solution

Control with an insecticide labeled for this pest, following label instructions.

Close

Aster Leafhopper -

Image of Aster Leafhopper
Aster Leafhopper
Description
Spotted, pale green insects up to 1/8 inch long hop or fly away quickly when a plant is touched. The leaves are stippled and may turn brown.
Analysis

Macrosteles fascifrons This insect, also known as the six-spotted leafhopper, feeds on many vegetable and ornamental plants. It generally sucks the sap from the undersides of leaves, which causes stippling. This leafhopper transmits aster yellows, a plant disease that is quite damaging. Leafhoppers at all stages of maturity are active during the growing season. They hatch in the spring from eggs laid on perennial weeds and ornamental plants. Even cold areas where eggs cannot survive the winters are not free from infestation, because leafhoppers migrate in the spring from warmer regions.

Solution

Apply an insecticide labeled for aster leafhopper, following label directions. Use row covers over the plants to keep leafhoppers out. Eradicate nearby weeds-especially thistles, plantains, and dandelions-which may harbor leafhopper eggs and aster yellows.

Close

Cabbage Looper -

Image of Cabbage Looper
Cabbage Looper
Description
Leaves have round or irregular holes. Green worms up to 11/2 inches long, with light stripes down their backs, feed on the leaves or heads. Masses of green or brown pellets may be between the leaves.
Analysis

Trichoplusia ni Although several worms attack lettuce, the most damaging is the cabbage looper. The looper attacks all varieties of lettuce, as well as members of the cabbage family. Adults lay eggs throughout the growing season. The brownish cabbage looper moth lays pale green eggs on the upper sides of leaves in the evening. The worms eat lettuce leaves and heads, and their greenish brown excrement makes the plants unappetizing. Worms may be present from early spring until late fall. In the South, they may be present year-round. Worms spend the winter as pupae attached to a plant or nearby object.

Solution

Use row covers to keep adults from laying eggs. Clean all plant debris from the garden to reduce the number of overwintering pupae.

Close

Cutworms - Lettuce

Image of Cutworms - Lettuce
Cutworms
Description
Young plants are chewed or cut off near the ground. Gray, brown, or black worms, 11/2 to 2 inches long, may be found about 2 inches deep in the soil near the base of the damaged plants.
Analysis

Several species of cutworms attack plants in the vegetable garden. The most likely pests of lettuce plants in the spring are surface-feeding cutworms. A single surface-feeding cutworm can sever the stems of many young plants in 1 night. Cutworms hide in the soil during the day and feed only at night. Adult cutworms are dark, night-flying moths with bands or stripes on their forewings. In southern parts of the United States, cutworms may also attack fall-planted lettuce.

Solution

Apply an insecticide labeled for cutworms, following label directions. Turn the soil over thoroughly in late summer and fall to expose and destroy eggs, larvae, and pupae.

Close

Downy Mildew - Lettuce

Image of Downy Mildew - Lettuce
Downy Mildew
Description
Angular sections of lettuce leaves turn light green, then yellow. These sections are limited by the leaf veins. Later, white fuzzy growth appears on the undersides of the sections. Affected leaves may turn brown and die.
Analysis

This plant disease is caused by a fungus (Bremia lactucae) that attacks only lettuce and some of its wild relatives, especially prickly lettuce (Lactuca serriola). It is seen most commonly at harvest time because it usually infects mature plants, but it also infects seedlings and transplants, which may die. Downy mildew is favored by cool (less than 70&deg;F), humid weather. Spores are released on humid mornings with more than 50 percent relative humidity, beginning at sunrise, and are blown by the wind onto plants. Morning dew persisting past 10 a.m. especially favors infection. This fungus mutates readily, and several distinct strains exist.

Solution

Avoid watering with a sprinkler, especially early in the morning when it extends the damp period begun by morning dew. Drip irrigation under a mulch helps keep humidity low around the plants. The best prevention is to plant resistant lettuce varieties. Strains of fungus constantly adapt to overcome resistance, so experiment to find the best ones for your area. Clean up and dispose of debris immediately after harvest.

Close

Mosaic Virus - Lettuce

Image of Mosaic Virus - Lettuce
Mosaic Virus
Description
Leaves turn yellow or are mottled light green and yellow. The veins are pale, and the leaf edges may curl inward or be ruffled. The plants are stunted, and heading varieties don''t produce heads.
Analysis

This plant disease is caused by at least two viruses that attack all varieties of lettuce. The viruses usually enter the garden in infected seed, but they may also live in weeds, including wild lettuce, pokeweed, wild cucumber, and groundsel. Once the infection is present in the garden, aphids-primarily the green peach aphid-spread the viruses from plant to plant. The viruses can also be transmitted mechanically as diseased and healthy plants rub together. Symptoms appear 8 to 14 days after infection. Occasionally a plant will show symptoms but then recover and grow to normal size.

Solution

Discard severely infected plants; they will produce very little. If the plants are infected just before harvest, lettuce is still edible. Buy lettuce seed from a reputable company, and select resistant lettuce varieties. Apply an insecticide labeled for aphids, following label instructions.

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