Austree, a hybrid willow, is sometimes used in windbreaks, hedges, or as a shade tree. They have become popular because of their ability to grow fast, advertised as growing up to 15 feet per year. But with the good growth come the price homeowners have to deal with, a destructive leaf blight disease caused by the fungus Venturia saliciperda.
Rainy spring weather favors infection. Fungal lesions appear on the underside of affected leaves. After growth starts in the springtime, a few small leaves turn black and then die. Then, all the remaining leaves on affected twigs suddenly wilt and turn black. Affected leaves may look as if they have been burned by fire and then fall off from the tree. A heavy leaf infection in spring may lead to the formation of cankers on twigs.
Pruning dead twigs and branches, and raking fallen leaves can help reduce the source of infection for next year. Chemical sprays that are labeled for control of leaf blight include Bordeaux mixture, copper-based fungicides, and lime-sulfur. To protect new growth, two to three applications at labeled rates are recommended in spring when leaf buds begin to open.
This article originally appeared in the July 16, 1999 issue, p. 97.