Chlorothalonil and Anthracnose on Japanese Maples

Anthracnose

• Anthracnose on a Japanese maple tree is caused by several different species of fungi and results in the scorching of sections of leaves and the formation of dead spots. The symptoms are exacerbated by wet weather in late spring or early summer as tan lesions develop on the foliage of a Japanese maple. These lesions eventually grow together and kill large sections of each leaf, with a severe case of anthracnose leading to near-total defoliation of the tree.

Significance

• Fruiting bodies of the fungi -- called acervuli -- may appear on the upper or lower surface of Japanese maple leaves. Anthracnose overwinters on twigs or fallen leaves and spreads easily through wind-blown rain. The disease will often become less problematic as summer persists and the dry season commences. While the fungus damages the aesthetic appeal of the tree, it rarely results in long-term damage to the health of a Japanese maple.

Prevention/Solution

• Because anthracnose overwinters on fallen leaves and twigs, the removal and destruction of that litter is mandatory to help prevent the further spread of infection. Fungicide is rarely recommended because the disease is usually not fatal and the cost of treating mature Japanese maple trees can be extensive. If fungicide is utilized, it should be applied immediately upon bud break and once or twice again, at intervals of approximately two weeks, to further treat the disease as new foliage expands.

Chlorothalonil

• Chlorothalonil is a general-use fungicide that is utilized to control fungi that afflict Japanese maples and a wide variety of other plants. It is sold under a variety of brand names and in different compounds with other pesticides. It is known to be somewhat toxic to mammals and can result in eye and skin irritation. People who work closely with the tree after applying chlorothalonil are likely to suffer from dermatitis and experience swollen and inflamed upper eyelids.