This leaf-spot disease is caused by a fungus (Colletotrichum) that is most active in warm, wet weather. The fungus spends the winter in dead plant tissue. It spreads new spores in the spring. Leaves must be wet for an extended period before infection can take place.
Remove and dispose of the infected leaves. Avoid overhead irrigation in the evening when leaves will stay wet for hours. In the fall, remove and dispose of all dead leaves to prevent the disease from returning next year. When planting hosta, space plants far enough apart for good air circulation and quick drying.
This plant disease, also known as Southern blight, is caused by a fungus (Sclerotium rolfsii) that lives in the soil. The fungus is widespread in the South and attacks many types of plants. It spreads by moving water, diseased transplants, infected soil, and contaminated tools, traveling short distances over the soil to attack adjacent plants. The fungus produces tiny ''mustard-seed'' pellets, called sclerotia; these are white when young, maturing to dark red or brown. Sclerotia survive many years in soil, infecting healthy plants when conditions are suitable, especially in hot, humid weather. In the early 1990s, the disease appeared on hostas in the upper Midwest, perhaps coming from southern-grown plants. It survives cold winters.
Infected plants cannot be cured. Remove and discard infected plants and don''t transfer soil or plants to other parts of the garden. If possible, also remove the infected soil to a depth of 8 inches. Replant with resistant plants. Clean tools, shoes, and wheels thoroughly. Keep the soil immediately around plants in the diseased area free of mulch and plant debris.
Aphelenchoides fragariae This disease is caused by a nematode that infests hosta leaves. Nematodes are microscopic, clear worms that usually infest plant roots, but this one infests the foliage of many plants. Nematodes enter leaves through the breathing pores. Inside, they feed on the tissues and may kill them. Leaf veins act as barriers until the leaf is wet; then the nematode swims through the water to infect other leaves. Foliar nematodes reproduce rapidly and are most damaging in wet-summer, warm regions of the country. They live in soil and dead plant tissue for years; some plants harbor them with no symptoms.
Remove and destroy infested leaves or plants by putting them in the trash. Do not compost them. Avoid wetting leaves when watering. Mulch the ground under plants; nematodes cannot move on dry surfaces. Remove dead foliage from the garden in the fall. Check new plants carefully for disease, and do not replant hostas in infested soil. Apply insecticidal soap if symptoms appear.
This virus infects only hosta plants. This extremely contagious disease was first identified in 1996, but it may have been present before that. In 2003 and 2004 the number of infected plants grew rapidly, and the disease is now very wide-spread. The virus develops for 3 or more years with no symptoms, but meanwhile the plant is contagious to other plants. Because the disease is not yet well-known, it has spread rapidly in the stocks of hosta growers in the United States and Holland-many hostas for sale are infected. Avoid purchasing hosta plants with uneven color, blotchiness, or puckered or twisted leaves, and don''t purchase any hostas from a nursery that has suspect plants in its collection. Some varieties may be more resistant to the disease than others, but they have not yet been identified, so a reliable list is not available.
The disease spreads through sap. Avoid bruising or crushing hostas and keep lawn mowers and string trimmers away. Disinfect tools and hands between plants. Destroy and discard diseased plants, including their roots, in a sealed garbage bag. Don''t plant hostas in the same location until any remaining roots decompose. Destroy the entire batch of purchased hostas if any of them develop symptoms.
These pests are mollusks and are related to clams, oysters, and other shellfish. They feed on a wide variety of garden plants. Like other mollusks, snails and slugs need to be moist all the time. For this reason, they avoid direct sun and dry places and hide during the day in damp places, such as under flowerpots or in thick groundcovers. They emerge at night or on cloudy days to feed. The young look like miniature versions of their parents.
Apply a pesticide labeled for slugs and snails, following label directions.
Hostas are shade plants and cannot tolerate too much direct sun. Sunlight breaks down chlorophyll, the green pigment in plant leaves. Hostas cannot replace the chlorophyll as fast as it is destroyed, and bleach to a cream or white color. If the leaf remains in direct sunlight, the bleached areas then burn from overheating and die, turning tan or brown. They can tolerate more morning sun than afternoon sun, and tolerate more sun in cool weather than in hot weather.
You cannot repair the damaged leaves. Remove them if they are unsightly. To avoid further damage, move the hostas to a more protected location, or create some shade for them.