Dogwoods & Black Stem Disease

Disease Identification

• Dogwoods are susceptible to the fungal disease called dogwood anthracnose or black stem disease. The infection was identified in the late 1970s and occurs in trees growing in landscapes as well in forests. Dogwood anthracnose is caused by Discula destructive, a non-native pathogen that entered the country though infected dogwood trees.

Symptoms

• Earliest sign of infection is the appearance of spots on foliage and flowers on lower tree areas in May and June. The brown, irregularly shaped spots have reddish purple borders. The infection gradually spreads upwards through the tree and to the stems. Young stems turn dark or blighted and older branches develop cankers or sunken, dead areas. The dead foliage remains attached to dead stems. Severe infection leads to branch dieback. Cankers on main trunk are likely to kill the tree.

Favorable Conditions

• Fungal growth is rapid in high humidity and in cool temperatures ranging between 60 to 70 degrees F. Trees growing in areas of full sun that are also suffering from drought and winter damage are more likely to get infected. The use of overhead irrigation in trees spreads and disperses the spores to other dogwoods in the areas. Dogwoods that are planted in heavy shade are also more prone to infection as compared to trees in filtered light.

Control

• Do not plant imported dogwood trees close to native trees as this increases chances of infection. Select an area that receives morning sun and afternoon shade for planting dogwoods. Make sure there is good air circulation around the tree. Do not use overhead irrigation to water trees and apply mulch to conserve soil moisture and reduce chances of drought. Chemical control options include the use of propiconazole, myclobutanil or chlorothalonil. All chemicals are sold under different tradenames.