Hosta Diseases & Parasites

Viral Diseases

• The symptoms of a viral infections include circular spots with concentric rings, puckering of leaves, and discoloration. Viruses are spread through contaminated tools or by insects that pierce infected leaves then feed on uninfected leaves. Hosta X virus creates mottle blotchy coloring as well as circular spots with rings around them. On hostas with gold foliage, the virus often produces green streaks. Viruses that affect other plants can also infect hostas, such as Impatiens necrotic spot virus, tomato ringspot virus, tobacco rattle virus and Arabis mosaci virus. Viral infections cannot be cured, and once a plant contracts a virus it should be destroyed so that other plants aren't infected.

Bacterial Diseases

• Bacterias are single-celled creatures that invade hostas through some sort of injury. Sometimes, excessively cold temperatures encourage the disease. Bacterial soft rot affect the petioles and lower leaves and crowns of hostas, causing a wet decay with a bad smell, said to resemble the smell of dead fish. The disease seems to emerge more frequently during high temperatures that include high humidity. Infected plants should be destroyed to prevent passing the infection to other plants. Be sure all tools used on the plant are sterilized. Pre-treat the soil with fungicides including copper before replanting.

Fungal Diseases

• Fungal diseases grow best in moist circumstances, an environment also favored by hostas. Fusarium fungi affects leaves, crowns and roots, depending on the species. Infected plants are stunted and leaves develop necrotic zones. Anthracnose produces tan spots with dark borders. Petiole rot produces fungal growth at the base of the plant, then affects the leaf's petioles, cutting off nutrition to the leaf. Phytophthora creates watersoaked spots and affects the whole plant. The fungus remains in the soil. With all fungal diseases, remove all affected foliage and destroy, and sterilize all tools used. Most fungal infections can be avoided with regular morning irrigation, good drainage, and by keeping leaves as dry as possible.

Parasites

• Foliar nematodes are parasites that affect hostas and other plants. It's a microscopic, worm-like creature that feeds on or within the hosta tissue. Symptoms include chlorotic, linear lesions that fall between the leaf veins because the veins limit the movement of the nematodes. Nematodes are spread by splashing water or rainfall, so keeping leaves dry is one preventative measure. One last-ditch effort to save a plant that's severely infected includes drenching the leaves in hot water that's between 70 to 90 degrees Celsius (158 to 194 degrees Fahrenheit). It may save the plant, but it may also kill it. However, the plant would need to be destroyed anyway to avoid infecting other plants.