Leaf blight can be a very destructive disease on pachysandra. The disease is caused by the fungus Volutella pachysandrae, and may be worse where plants are under stress.
Irregular spots or lesions are first seen in the early summer (Fig. 1). Infected leaves and stems exhibit brown blotches on leaves and/or brown shriveled stems (Fig. 2). The planting of pachysandra may become thin as the disease progresses. The leaves may appear orange due to the presence of spores of the fungus.
In the spring, the fungus produces pinkish spores (in sporodochia) on infected tissue. During wet weather in summer and fall, buff to orange colored masses of spores are produced in fruiting stuctures known as perithecia. Both spore types cause new infections and help spread the fungus. They are carried by splashing or running water or during wet weather. Weak or injured plant material is much more susceptible than healthy tissue, so damage may be very severe when plants have been stressed by excessive sunlight, winter injury, drought, or insect attack. Spread of the fungus is also more rapid in dense plantings or where heavy mulches are used.
New infections may occur any time during the growing season. These are apparent on the undersides of leaf lesions and along stem lesions. Small lesions develop and may continue to expand until the entire plant is killed. If blight is suspected, but fruiting bodies are not evident for diagnosis, placing infected material in a plastic bag with a moist paper towel for several days should cause them to develop.
Always work in plantings when they are DRY to reduce disease spread. Remove all severely infected plants. These should be buried or thrown out with the garbage. General thinning of the planting to promote good air circulation will help reduce spread by allowing plants to dry out more quickly after rain.
Disinfest pruning tools by swabbing the cutting blades with a solution of 7 parts rubbing alcohol and 3 parts water between each cut. Avoid the use of mulches that promote high moisture around the plants and remove tree leaves that cover the planting in the fall.
After the above cultural practices are completed, fungicide sprays may still be needed in some cases to prevent further spread of the disease. Homeowners in New York State may use one of the following fungicides containing the active ingredient chlorothalonil according to label directions when new growth begins in the spring: Fruit Tree, Vegetable & Ornamental Fungicide (EPA Reg # 60063-9-54705) or Garden Disease Control Concentrate (EPA Reg # 239-2522).
Since insect infestation can weaken plants and thus cause more severe leaf blight, management of insect pests is advised. The insect that most commonly causes this sort of problem is euonymus scale. If scale infestations are small, prune out affected plant parts.
This publication contains pesticide recommendations. Changes in pesticide regulations occur constantly and human errors are still possible. Some materials mentioned may no longer be available, and some uses may no longer be legal.
TK: 5/2008 #127
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