Dogwood Decline

Since the late 1970s, dogwood trees (Cornus florida L.) throughout their range have suffered from severe twig dieback, trunk cankers, and general decline, in addition to the anthracnose (petal, leaf, and fruit spotting). Yearly growth in trunk diameter has decreased markedly since 1976. The anthracnose and canker-causing fungus Discula destructiva is a very important part of the tree decline and death. Trees in exposed sites as well as in the forest are dying. Anthracnose is particularly severe when wet weather coincides with bud break and leaf enlargement. The fungus overwinters in infected twigs, in cankers (dead bark areas on the trunk), on dead leaves that remain on the tree during winter, and on infected fallen leaves. It is thought that Discula was inadvertently introduced into the U.S. on infected, symptomless trees in the 1970s and that migrating songbirds, having eaten Discula-infected dogwood fruits, spread the fungus throughout the natural range of Cornus florida. Prior to the 1970s, spot anthracnose (caused by the fungus Elsinoe) was the main leaf spot on dogwoods. That fungus was also inadvertently introduced to the U.S., probably in the 1940s. However, Elsinoe does not cause a branch dieback.

Symptoms of Decline

• Twigs and lower branches die.
• Cankers (abnormally roughened areas, either slightly sunken or raised) form on twigs, branches, and trunks.
• Secondary fungi and dogwood borers are in the trees.
• Water sprouts develop at the base of the tree. Sprouts die.
• Tree growth slows and tree dies.

Management of Dogwood Decline

The following steps are recommended to protect healthy trees.

• Promote tree vigor.
  • During dry summer and autumn weather, water once every 7-10 days to supply 1 inch of water.
  • Fertilize moderately in the spring. Do not apply excessive nitrogen.
  • Do not injure trees with lawnmowers.
• Remove sources of fungus.
  • Rake and remove fallen leaves and twigs.
  • Prune water sprouts and dead twigs and branches and dispose of them. Do this only during dry weather when plant surfaces are dry.
  • Remove severely affected trees.
• Protect trees from pests.
  • As buds begin to open and until leaves are fully expanded or the weather dries, apply a fungicide that contains chlorothalonil, propiconazole, or mancozeb to control anthracnose.
  • In May and early June, control dogwood borer.

When purchasing dogwoods, examine the lower trunk and branches and reject those with any abnormal blemishes, cankers, or dead areas. Petal and leaf spots may be small (1/25-1/16 inch), circular to elongated and reddish-purple. Centers turn pale yellow-gray and drop out (spot anthracnose, caused by Elsinoe), or damaged areas may be large, brown, irregularly shaped spots with dark gray-green, purple, or brown margins. Tiny brown dots are seen inside some spots. Dead leaves often remain attached to the tree.

Fungicides mentioned above:

COMMON NAME	TRADE NAME
chlorothalonil	Daconil 2787
mancozeb	Dithane, Penncozeb
propiconazole	Banner