Do You Need to Remove Chinese Elm With Anthracnose?

Cause

• Spores of the anthracnose fungus are generally present in the environment. They overwinter in the leaf litter beneath a tree, and in dormant buds. When conditions are right, such as during spring rains, the spores become active and infect the tree's foliage, relying on water splashing from the soil to carry them onto the tree. While healthy trees often can resist infection, Chinese elms under stress from drought, insect infestations or other damage are susceptible to anthracnose. The disease is more common when spring weather is cool and wet, or when you water the tree instead of the soil. The disease affects Chinese elms grown along the coast more than inland trees.

Symptoms

• Tiny yellow spots on the top surface of the leaves may be the first anthracnose symptoms you'll notice. The spots darken until they are black and appear dead, and the leaves may become distorted and fall from the tree. Severe infections can cause complete defoliation. The trees may develop cankers, which are sunken, diseased areas on woody parts of the tree, especially on the trunk. Chinese elms grown in cool, moist areas are more likely to die from anthracnose than are those in warmer, inland regions.

Cultural Control

• To help control anthracnose, remove leaf litter that may harbor overwintering fungus spores from beneath the Chinese elm. Don’t water the foliage on the tree. Instead, irrigate the soil out to the tree’s drip line. Remove dead branches, and cut infected branches back to healthy wood. Provide increased air circulation within the tree by removing overgrowth in the canopy. Cut out small cankers on the trunk and larger limbs until you reach one-half inch into healthy wood.

Considerations

• Large trees are expensive to treat, and plant pathologists at the University of Arkansas say treatment of large trees isn’t warranted. Instead, consider removing the large, heavily infested tree, and replacing it with a cultivar that is less susceptible to the disease. University of California specialists suggest the “Drake” Chinese elm cultivar for its disease resistance. Treat small trees with a preventive fungicide. Your local county cooperative extension office can advise you on the best anthracnose treatment for your area.