In the past two weeks, I discussed powdery mildew and spot anthracnose, which are diseases affecting dogwoods. Therefore, this is the third and final article focusing on the details about dogwood anthracnose.
Dogwood anthracnose is a relatively new disease of dogwood. It is a serious disease capable of killing large numbers of trees and most dogwood species can become infected.
Dogwood anthracnose is most severe in areas of the state higher than 2,000 feet in elevation. A few cases have been reported at lower elevations where dogwoods are grown in very cool, moist, shady locations.
The first symptoms are spots on the leaves and flower bracts that appear in the spring. Infected leaves have tan spots with purple edges, dry brown margins or large blotches on them. Blighted gray or drooping leaves hang on the twigs and are often the first symptoms noticed during cool, wet weather.
The infection spreads into the shoots, main branches and trunk, causing brown sunken areas (cankers) to occur. Cankers can girdle and kill individual branches or twigs. Multiple cankers can girdle the main trunk and eventually kill the tree.
Planting resistant species and cultivars is one of the better ways to manage this disease in the landscape.
Kousa dogwood (Cornus kousa) is generally resistant to dogwood anthracnose and is a better choice for replanting in sites where dogwoods have died from this disease.
Crosses between Cornus kousa and Cornus florida (Rutger’s hybrids) have greater disease resistance to dogwood anthracnose and include: “Aurora.” “Celestial,” “Galaxy,” “Ruth Ellen,” “Star Dust,” “Stellar Pink” and “Constellation.” Cornus florida “Appalachian Spring” has a high level of resistance to anthracnose.
A combination of cultural and chemical measures is necessary to control the disease. Effective control may be possible if the disease is detected before branch dieback begins.
During hot, dry summer weather, prune and dispose of all dead or cankered twigs and limbs. Remove all water sprouts. Rake and remove fallen leaves. Do not leave dead leaves attached to the tree. Improve air circulation and light penetration by removing understory plants and crowding vegetation.
Avoid high applications of nitrogen fertilizer, since this can promote very succulent but susceptible new shoots. Maintain healthy dogwoods by following recommended cultural practices.
Avoid transplanting dogwood seedlings from the woods as these plants may harbor the fungus.
Fungicide sprays to protect the new leaves and shoots need to begin at bud break in early spring. Fungicides for spot anthracnose also will help control dogwood anthracnose. These include: chlorothalonil, mancozeb, maneb, propiconazole, thiophanate-methyl or copper fungicides. Maintain a protective covering of fungicide when new growth is present. Apply all chemicals according to directions on the label.
Dogwood diseases can really be a problem in keeping trees looking good, but in general they can be kept to a minimum if we create an environment unfavorable for the disease. And if all else fails, use of fungicides is always a good management option.
Michael Wheeler is county extension coordinator for the UGA Cooperative Extension office in Hall County. You can contact him at 770-535-8293, www.hallcounty.org/extension. His column appears weekly and on gainesvilletimes.com/life.