Acer palmatum atropurpureum or Japanese red maple is a small, slow-growing ornamental tree or a multstemmed shrub. Leaves are red to reddish-purple in both the spring and fall. This lovely tree does well in full to partial shade. A mature Japanese red maple will reach a height of 15 to 25 feet, and a spread of 20. It is susceptible to verticillium wilt, phytophthora root rot, anthracnose, phyllosticta leaf spot and pseudomonas tip blight.
The fungus Verticillium dahliae is the cause of verticillium wilt. It survives in the soil as well as in the roots of an infected tree. Verticillium wilt spreads when the soil is cultivated, when infected pruning tools are used and by irrigation. Symptoms of the disease are wilting and sticking of leaves on branches. It occurs during the growing season and slowly progresses to other branches. Verticillium wilt can kill the tree--there is no known control or treatment method. The best way to manage verticillium wilt is to avoid planting in an infected area.
Phytophthora Root Rot
This disease begins below ground level with the fungus attacking the fine roots of the tree or shrub. The roots die because of the fungal attack, and the fungus then spreads to the larger roots, moving up to the root crown. As phytophthora root rot progresses, it spreads up through the stem or trunk, destroying tissue. Symptoms are chlorotic leaves (turning a lighter color and wilting). Above soil symptoms may not appear, and in some instances the tree or shrub could have symptoms for a year before dying. The best way to prevent phytophthora root rot is to maintain a healthy plant, which includes planting it in well-drained soil and not overwatering.
Anthracnose is a fungal disease caused by the fungus Gloeosporium apocryptum. The disease thrives in hot/wet weather and is characterized by round, slightly irregular brown spots on the leaves. Maintaining a healthy tree is the best way to control anthracnose. Opening up the crown by pruning select branches will allow better air circulation, which lessens the wet conditions that lead to anthracnose. Fertilization is also important as well as watering when necessary. Infected leaves should be raked up in the fall and disposed of to avoid further spread of the disease. Severe cases of anthracnose can be treated with a fungicide (following the manufacturer's directions).
Phyllosticta Leaf Spot
Signs of this fungal disease are tan circular spots outlined in purple or red. As the season progresses, the spots may also contain small black spots. This disease is cosmetic and causes very little damage. Fungicides are seldom necessary.
Pseudomonas Tip Blight
This is caused by Pseudomonas syringae, which develops in wet, cool weather. The bacteria is active in the winter, when the temperatures are below freezing. When freezing and thawing take place, cracks often are created in the trunks of plants, creating an entry way for the bacteria. Symptoms in early spring (late winter) are blackened stems, wilting/withering leaves and dieback of shoots. Control by chemicals is possible but expensive. Caution should be taken when purchasing a Japanese red maple--an infected plant can spread the disease to other plants in your landscape or garden.