Many types of plants are susceptible to diseases that can alter their health, sometimes causing them to die prematurely. Black spots are a common occurrence on a sick or diseased plant, and can be a symptom of several different diseases. Some of these are curable, while some may permanently alter the plant’s health. Even sturdy plants, such as grapevines, are not immune to such diseases. Some causes of black spots in grapevines are black rot, downy mildew and Eutypa dieback.
Black rot is a disease that is caused by a fungus, and is commonly found infecting grapevines throughout the Eastern United States and Canada. The characteristic symptoms of this disease include leaf lesions that develop a black border, with a pimple-like bump in the center of the lesion. Grape orchards that are infected with this disease can experience devastating loss. Luckily though, the disease can be controlled through the spraying of fungicide on the grapevines. With effective treatment, grapevines infected with black rot can usually be saved.
Downy mildew is another fungus-caused disease that can result in devastating crop loss. Symptoms of downy mildew include the appearance of small, yellow lesions on the leaves of grapevines that later turn black as a result of the death of the leaf. The disease tends to spread to other plants during rainy periods. Downy mildew can be controlled through the application of fungicide just before blooms appear on the plants. Usually, the same fungicide can be used to treat and prevent both black rot and downy mildew.
According to canr.msu.edu, Eutypa dieback is a very common disease that is found in about 10 percent of all concord grapevines in the state of Michigan. As with black rot and downy mildew, a fungus causes Eutypa dieback. The origination of the disease is usually a pruning cut on the plant. Fungus that is introduced into the plant through the cut causes the inner sections of woody grapevine canes to rot and die. Usually, symptoms do not appear until two to three years after the plant’s infection. Eutypa dieback can cause large sections of the grapevine to die, and may eventually kill the entire plant. There is no known treatment for this often costly disease, which can lead to the loss of many grapevines in an orchard.
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