My lily-of-the-valley ground cover appears to have died. I’m wondering what I did wrong. There are just a few leaves left and they have brown sections. Is there something that I should have done sooner or anything I can do now?
— Carrie Nichols, Grayslake
From your description, it sounds like your ground cover is showing anthracnose, which is a common disease caused by a fungus on lily-of-the-valley. It causes lesions that are often circular to oval-shaped and dark brown in color with purplish red margins. These spots can be ½-inch in diameter or larger and may fall out, exposing the veins in the leaves. Infected leaves can die prematurely. The bed of lily-of-the-valley in my garden recently died back with just a couple of diseased leaves left (like yours). My plants usually get anthracnose in late summer and look tattered from the disease, but this is the first time the plants have completely died. I am not worried about the plants nor am I doing anything special to help them. This disease is not usually fatal, but it does weaken the plant. The number of flowers is often reduced the year after infection with anthracnose.
Anthracnose will attack other plants in the garden too. It can cause brown spots that merge to form irregular dead areas on hostas that are in wet or overwatered areas. Coral bells may develop small brown spots on the leaves. Peonies get both anthracnose and botrytis. To make a precise identification, a lab would have to examine a culture from the affected plants. The diseases cause buds, flowers, leaves, and stems to die in spring and summer. Symptoms vary from plant to plant or even on the same plant depending on pathogen, host, time of infection, weather and so on. You may see large, irregular blotches on peony leaves at this time of year if a disease is present.
Anthracnose overwinters on dead plant material, so it is important to remove and destroy diseased foliage in the fall when you are doing clean-up. Badly infected foliage should be pruned out now and discarded. Anthracnose spores can blow for many miles. Wet conditions in the garden help promote infection and the spread of this disease, so site modification to improve air circulation and being careful not to overwater will help reduce the occurrence. Protective fungicide applications made in spring as the foliage emerges can be beneficial in some situations.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.