Blackwelder column: Spots on dogwood blooms could be anthracnose
Dogwood blooms are blooming, painting the county with much-needed color. Our state flower actually has white bracts, similar to the Christmas poinsettia bracts. The flower itself is the green bundle of buds located in the center of the bracts.
Unfortunately, some dogwood blooms are not so beautiful. From a distance some dogwood blooms look weak and stained. Some trees may not be affected, while only parts of a tree may succumb to the disease. Closer observation reveals distorted bracts with spots. Spot anthracnose is the culprit and is rampant on native dogwood trees this spring.
Many native dogwood flower bracts are infected with small, purple haloes. These spots or halos eventually merge, engulfing an entire flower bract. Severely infected flowers usually fall from the tree, while the remaining bracts become small and distorted.
The infection moves from infested bracts to the foliage later in the spring. Leaf spots are usually circular with a chocolate-like color. These spots elongate as the season progresses and the centers turn yellow, then gray. Heavily infected leaves may be smaller than normal, distorted and often killed. Infected young shoots and berries develop elongated, scabby lesions with a purplish margin. The causal fungus produces spores on the lesions and overwinters on infected twigs and fruit
Spot anthracnose is caused by the fungus Elsinoe corni and is usually not a problem if dry weather occurs before and during the bloom period. However, our area has had its share of wet, humid weather which promotes rapid spread of this fungus.
Fungicidal sprays are not mandatory, since spot anthracnose does not significantly damage dogwood trees. In most situations fungicidal sprays are impractical; however, foliar-applied fungicides control the fungus.
Foliar applications of mancozeb, daconil or other labeled fungicides must be applied at bud break, as flower petals fall, midsummer, and after buds are formed to prevent reoccurrence.
Unfortunately, native dogwoods seem to be the most susceptible to this disease, so avoid transplanting dogwood trees from the wild. Buying healthy trees from a reputable nursery will prevent spread of the disease.
Select a planting site with good drainage and filtered light which allows the foliage a chance to dry quickly. Avoid planting in deep shade. More information on dogwood spot anthracnose and other dogwood disease problems can be found online at http://www.ces.ncsu.edu/depts/pp/notes/Ornamental/odin23/od23.htm
Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension Service in Rowan County. Call 704-216-8970.
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