alternatives to pesticides - plant disease - Dogwood anthracnose
Not to be confused with the disease of oaks, maples, sycamores, and other plants, anthracnose is a common name used for many unrelated plant diseases that cause leaf spots and dieback. Because of its lethal effects on many species of dogwood, this particular fungus has earned the scientific name Discula destructiva. It attacks most species of dogwood, including flowering dogwood and our native dogwood, but does not occur on Korean (also known as kousa) dogwood. Diseased plants typically have spots on the leaves and flowers that are light to dark brown with purplish margins. These spots produce spores, which spread via wind and rain to other leaves and create more spots. Severely infected trees will have poor growth, produce few leaves, small leaves and many sprouts at or near the base of the tree, and will eventually decline and die.
Whenever possible, you should plant kousa dogwoods. They are lovely trees, with dark, glossy green leaves and creamy white flowers. There is at least one pink-flowering variety available as well. They bloom after other dogwoods, usually in June.
Rake up diseased leaves and remove them. Prune the tree to increase air circulation, which may lessen the occurrence of leaf spots. Also, infected trees often produce many sprouts at or near the base of the tree, which are especially susceptible to infection. These should be removed. Finally, be sure the tree receives adequate water, preferably from an irrigation source that does not wet the leaves.
Least-toxic chemical control
The only effective control is a chemical leaf spray available only through tree care companies. It must be applied several times a year, beginning in early spring.