Hostas are remarkably resilient plants that have become a mainstay of the shade garden. Hostas are for the most part trouble free when their basic needs are met: protection from direct sun (most varieties), ample watering, regular fertilization and division of crowded stands. However, a few issues do exist that affect the health and aesthetics of this favored perennial. Here they are:
Caused by a host of diseases occurring at once, anthracnose thrives in damp, still, part-to-full shade areas of the garden.
Signs: Tan or brown spots appear on hosta leaves and then enlarge and develop dark borders. The spots drop out, giving the leaves a tattered quality.
Action: Remove infected leaves, water at the base of the plant rather than from above, replace mulch and ensure there is room for air circulation between the plants. Treat with a fungicide to protect the remaining healthy leaves.
Formerly known as hosta crown rot, petiole rot is a serious fungal disease.
Signs: Yellowing and browning of the leaves around the margins, leaves become limp and mushy at the base of their petiole (leaf stem). The leaves are easily pulled from the main plant. White fungal threads (mycelium) may be visible. The disease fungus produces very small, round fungal seeds of sorts called sclerotia at the base of the petiole. Sclerotia can remain inactive in cold weather and are activated when the environment becomes warm and humid.
Action: Do not mound mulch around the base of any hosta, but especially those suspected to suffer from petiole or crown rot. Do not transplant any obviously infected plants or those you suspect may be infected. Remove infected tissue; taking care not to spread the fungus. Have a container handy for immediate disposal and isolation of infected plant material; seal it and place it in the trash, not a compost pile.
BACTERIAL SOFT ROT
Bacterial soft rot is caused by several types of bacteria and usually occurs where there is a wound from division or planting. Wounds may also be caused frost heaves over the winter.
Signs: Your nose will tell you that your hostas are suffering from bacterial soft rot. You will smell an offensive odor caused by the state of decay of the petioles and lower leaves. Leaves will turn yellow in color.
Action: Remove and dispose of infected plants. Thoroughly clean any tools that came in contact with the plant as well as your hands and gloves.
HOSTA VIRUS X
Hosta virus X is a vigorous spreader that may go undetected for years. The virus is often transmitted when cutting plants, during which time the infected sap of one plant comes in contact with a new plant.
Signs: Oddly patterned, yellowing tissue that looks thin and wrinkled. The colors of variegated leaves tend to blur together and lose their crisp definition.
Action: Use a discerning eye when purchasing hostas; avoid any whose leaves look suspicious. In the garden, destroy infected plants, thoroughly clean your tools and never divide an infected plant.
Signs: Older leaves develop light green to yellow stripes parallel to the major leaf vein. They take on a dry, tattered appearance.
Action: If you suspect foliar nematodes, do not water plants from above. Splattering water spreads foliar nematodes. Remove and destroy leaves with dead areas. Burn or bury infected plant material.