Extension Educator, Horticulture
Except for slug and vole feasts, hostas are generally considered disease and insect free. However over the last few years we are getting more than just slug complaints. Hosta problems may be showing up now.
Anthracnose is a fungal leaf disease of hosta that thrives in warm, wet weather. This is not the same fungus that causes anthracnose on sycamore and ash.
Symptoms of hosta anthracnose include large, irregular spots with darker borders. Eventually the centers of the spots fall out, and leaves become ragged. Usually this disease doesn't mean "hosta la vista baby," but it sure makes them look like they were in a gunfight.
Try to keep leaves as dry as possible by using soaker hoses or watering the soil rather than the plants. Improve air circulation as much as possible by dividing plants or selectively thinning trees. If anthracnose still seems to be a problem, it may be worth beginning a fungicide spray to protect the emerging leaves. Ideally fungicide application should begin in spring as new leaves emerge and as long as wet weather continues. Look for fungicides containing thiophanate methyl as the active ingredient. Always read and follow pesticide label directions. Check to see that the fungicide is labeled for hosta to control anthracnose or leaf diseases.
Although more common in southern states, Sclerotium blight can be a serious disease of hostas. Symptoms first appear as lower leaves wilt and brown. Eventually upper leaves wilt and show a soft, brown rot of the base of petioles. This disease is difficult to control since the fungus can reside in the soil.
Leaf nematodes can also be a problem on hosta. Damage appears as brown areas between veins. Sunburn is not an infectious disease and appears as tan or whitish areas on the leaves.
Get an accurate identification of the problem before starting any control measures. Avoid wetting leaves and crowded plantings. Check out Focus on Plant Diseases for some great pictures of hosta problems. Contact your local Extension office or the U of I Plant Clinic for assistance.