The Q&A Archives: Mottled Dogwood

Question: My young tree is being attacked by something. It started two weeks ago & my gardener told me to spray for various insects. I'm not sure this helped. The young leaves are turning brown on the edges & other leaves are shriveling up. Please help!!!

Answer: Browning leaf edges are rarely caused by insects, but can indicate either a disease or over- or under-watering. Here are some of the more common maladies of dogwoods:

The poor appearance of dogwood trees is often due to factors or conditions other than diseases, with symptoms the same as might be expected with a damaged or inefficient root system. These include stunting or slow growth, light green to yellow foliage, dead leaf margins, dieback of branches or even death of the plant. Marginal leaf burn and premature reddening of the leaves are common symptoms on dogwoods during the summer months when rainfall is below normal. Any situation in which the leaves are losing water faster than the plant can take it up can result in these types of symptoms.

Dogwoods are susceptible to several root and crown rot fungi. These fungi may be present in the soil and attack the roots when the vigor of the tree is reduced by unfavorable soil conditions or by some type of injury. Often the first symptom observed is the drying of the leaf margins followed by death of the plant during the summer months. This is the final stage of a disease that began with an infection of one or more of the lateral roots. After infecting a part of the root system, the fungus spreads along the roots to the basal portion of the tree, which is often girdled. As the fungus progresses, the tree may show symptoms of decline, such as yellowing of the foliage, dying of the leaf margins, branch dieback, and a general unthriftiness. One of the most common root rots on dogwood is caused by Armillaria sp. This disease is characterized by a relatively thick, white, fan-shaped mass of fungal tissue (mycelium) beneath the bark at the base of the tree or on large roots, and by black, shoestring-like structures (rhizomorphs) that can be found on or under the bark and in the adjacent soil. Another root rot, caused by Phytophthora cinnamomi, usually affects the smaller roots and occurs most commonly in poorly drained soils. This disease can be diagnosed only by laboratory tests.

To prevent root rot, plant only in well-drained soils where root rot has not been known to occur, preferably away from areas where large trees have been removed. Fertilize and water during dry periods and control foliage diseases to maintain the vigor of the tree. By the time a general decline of the tree is observed, it is too late to save it. Remove the tree and all roots possible from the soil, since the fungi can persist in dead roots and infect nearby shrubs or other plants set in the same site.

Powdery mildew, caused by Microsphaera pennicillata, produces a whitish growth over leaves, buds and young shoots. Young plants and actively growing plant tissues are more severely damaged than older plants or tissues. Infected leaves may be dwarfed, curled, or otherwise deformed. The disease may occur throughout the growing season.
Crown canker, caused by Phytophthora cactorum, is characterized by a slowly developing canker on the main trunk near the soil line. The disease usually occurs on newly transplanted trees or those that have injuries to the roots, and is more common on poorly drained areas. Cankers appear as constricted or sunken areas that may eventually girdle the stem and kill the top of the tree. Leaves on diseased trees may be smaller than normal, become chlorotic and be shed prematurely.

Hope this information is helpful and helps you discover the problem with your dogwood.

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