How To Keep A Dogwood Tree Healthy

QI have a 20-foot dogwood with the anthracnose disease problem, and the leaves curled up last year despite my use of a timed, quarterly spray service in my yard; I think they spray a combination insecticide and fungicide. What can I do to protect my dogwood?

A: Often the timing of a set spray will not occur when the protection is needed for your plants. WSU Extension specialists suggest that it is more effective to aim your control measures at a specific pest, with an understanding of the pest's biological cycles, than it is to have a nonspecific spraying done.

Pests, including fungal diseases, do not read the calendar; they are triggered by temperature, light intensity and other weather conditions.

Dogwood anthracnose is caused by a fungus that overwinters in the fallen leaves and dead twigs of affected trees. Your first line of defense is to prune out the dead twigs and branches and to rake up and dispose of all fallen leaves under the tree. Don't compost them; get them out of your yard.

Some gardeners, after raking up the dogwood leaves, mulch under the trees with leaves or organic materials that have not been affected by the fungus to offer further protection from rain-splashed fungal spores. Continue raking as leaves fall during the growing season; affected leaves will frequently fall off.

Having the tree planted where it gets good air circulation and sunshine will also help by allowing the branches and leaves to dry off. Keep your tree healthy - water it during the summer if it is an Eastern dogwood (Cornus florida). The Eastern dogwood is native to woods that receive considerably more summer rain than we do here in the Pacific Northwest. Many dogwood can survive these infections even if they recur for years.

To use a fungicidal spray for anthracnose control, watch the tree carefully. Spray at bud break (many dogwood have already begun to open their buds) and at 10-14 day intervals until the weather is dry. As you can see, one spray only or a spray at the wrong time wouldn't retard the infection. Microcop is one fungicide registered for this purpose.

Choosing the Kousa dogwood, Cornus kousa, may also reduce your likelihood of serious infection; while these dogwood, which beautifully bloom in June, occasionally get a touch of the disease, they are not as severely affected as either the native Western dogwood (Cornus nuttali) or the Eastern dogwood (Cornus florida).

Gardening runs Friday in Scene and Sunday in Home/Real Estate. It is prepared by George Pinyuh and Holly Kennell, Washington State University/King County Cooperative Extension agents, Mary Robson, Master Gardener program assistant, and volunteer Master Gardeners.