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Problem
(factsheet)
Plant NameTypeDescription 
AnthracnoseLettuceDiseaseAnthracnose of lettuce is a fungal disease favored by cool, wet weather. The disease is also known as shothole because of the characteristic symptoms. Lower leaves develop small, water-soaked spots which quickly darken and enlarge. The centers dry and drop out, leaving "shotholes" with black margins in the leaves. Affected leaves tend to wither and die quickly, then break off. The disease progresses to the younger leaves and may also cause symptoms on the midribs. The fungus is spread by splashing water and can be serious during prolonged wet weather. Some weed species are also hosts of the fungus.
Aster yellowsLettuceDiseaseAster yellows is caused by a phytoplasma which is a microorganism found in the phloem tissue of a plant. The phytoplasma is spread by leafhoppers and can also affect carrot, onion, potato, celery, and other crops, weeds, and ornamentals. Initial symptoms are seen on young leaves in the heart of the plant. These leaves turn yellow and may fail to develop normally, resulting in a thickened, stubby appearance. Affected leaves show characteristic pinkish or tan latex deposits on the underside of the midribs. Young plants may show yellowing of the outer leaves and severe stunting, while older plants may show only internal symptoms and the latex deposits.
Beet western yellows virusLettuceDiseaseBeet Western Yellows is a virus which affects many garden plants and weed species. The virus is transmitted by aphids, including the green peach aphid. Older leaves are affected first. Yellowing begins at the margin and progresses inward, with the veins typically remaining green. The disease results in reduced, abnormal growth of the plants. Symptoms tend to be worse when unfavorable conditions such as poor nutrition or poor root development are also present.
Bottom rotLettuceDiseaseBottom rot of lettuce is caused by a soil-borne fungus that is common in wet soils. Head lettuces, particularly the 'Big Boston' types, are attacked as they near maturity. The stems and midribs of lower leaves develop sunken, brown, necrotic spots which may enlarge to involve the entire stem or midrib. The surface of the spots may show a brown exudate or may be covered with a white to brown growth of the fungus. Brown or gray-brown fruiting bodies of the fungus can also be present in the lesions. Infected heads become slimy and later dry into a blackened mummy. Bacterial rots often attack lettuce after infection by bottom rot. The fungus causing bottom rot of lettuce also commonly causes damping-off of seedlings and seed rots in many species of plants.
Damping-offLettuceDiseaseDamping-off is caused by fungi that remain in the soil for long periods of time. Seeds decay without germinating. Seedlings may be infected and fail to emerge from the soil. Emerged seedlings are also attacked, causing them to wilt and topple over. Water-soaked or brownish lesions are often visible on the stem at the soil line. Plants become more resistant to attack as they mature. Damping-off fungi are more of a problem in cold soils with poor drainage, and in conjunction with overwatering.
Downy mildewLettuceDiseaseLettuce downy mildew is caused by a fungus which survives the winter on wild hosts and weeds. Light green or yellowish areas on the upper leaf surface are in places where the fungus is growing as downy patches on the undersides of the leaves. Affected parts turn brown and leaves die. Older leaves are infected first. This disease is worse in damp, foggy weather and between 43 and 53 degrees F.
Lettuce big vein virusLettuceDiseaseLettuce Big Vein Virus is transmitted by a fungus which inhabits the roots. Virus infection causes tissues next to veins to become clear, resulting in an enlarged appearance of the veins. The vein clearing becomes more severe with time. Leaves become puckered and mottled in appearance. Outer leaves may grow more rigidly upright than normal leaves. The heads may be loose and smaller than normal or slow in developing. The disease is more prevalent in poorly-drained soils and causes more severe symptoms in cool weather (below 60 degrees F). The virus can persist in the resting spores of the fungus for ten or more years.
AphidsLettuceInsectAphids are small, soft-bodied, pear-shaped insects. They may vary in color from yellow to green to dark. Aphids typically feed in colonies on the leaves, often preferring the newer growth. Infested leaves turn yellow and may wilt or show other signs of water stress. Feeding aphids often produce large amounts of honeydew, a sweet, sticky material which may attract ants or become covered with a dark growth of sooty mold. The ants may protect aphid colonies from predators.
SlugsLettuceInsectSlugs are common garden pests in western Washington. They resemble snails, but lack shells. They may vary from as little as 1/4" up to several inches in length, depending on age and species. Slugs often leave behind a characteristic slime trail, which appears silvery when it dries. Slugs typically feed at night and do more damage during cool, moist weather. Seedlings and small plants may be completely eaten, while larger plants may show only holes in the leaves.