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|This disease is most easily identified on peach. Symptoms are predominantly foliar, but the fruits may also be affected.
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X-DISEASE (Mycoplasma disease of peaches and nectarines)X-disease has been diagnosed in several peach orchards in northern Ohio. Once the disease is established in an area or orchard, it can be very destructive. The disease has been reported to occur primarily in the Great Lakes states and in the province of Ontario, Canada. The range of distribution for X-disease corresponds to the range of distribution of the wild chokecherry, which is a major reservoir of infection. X-disease can affect peach, nectarine, sweet cherry, and sour cherry.
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Reference: Ohio State University Extension
Symptoms on Peach
Figure 1. Symptoms of X-disease on peach leaves.
A good diagnostic symptom is the presence of apparently healthy twigs or branches with normal-looking leaves mixed with twigs or branches showing the symptoms described earlier. This mixture of healthy and diseased branches on the same tree occurs primarily during the first and second year's of infection. Two to three year's after initial infection, most branches will show symptoms.
Another important diagnostic aid is to pull a tree and examine the roots. Foliar symptoms of yellowing and stunting can also be caused by Phytophthora root rot, which has also been observed in several northern Ohio orchards. With Phytophthora root rot, the above-ground symptoms are usually fairly uniform throughout the canopy of the tree. You generally will not see a healthy branch on the tree with all other branches showing symptoms.
In addition, the crown and/or roots of a tree with above-ground symptoms caused by root rot should have visible, rotted areas. These areas are generally brick-red to brown in color and are often characterized by a sharp line of demarcation between healthy and diseased tissue. Roots on trees affected by X-disease appear normal.
Fruit set on trees infected with X-disease may appear nor-mal at first, but fruit on infected branches will usually drop prematurely.
Symptoms on Cherry
Trees on mahaleb rootstock generally react differently to the disease than do those on mazzard rootstock. Cherries on mahaleb rootstock are killed suddenly in midsummer by the disease. Trees on mazzard rootstock decline slowly. Infected sweet cherry trees on mazzard rootstocks may not show decline for many year's; often the only recognizable symptom is on the fruit. Scattered fruit on trees propagated on mazzard rootstock are small and pink at harvest and have a bitter flavor. Sour cherries seem to be a little more seriously affected in that dieback and decline are often associated with the disease.
Figure 2. X-disease on peach. Note the apparently healthy branch
among severely infected branches with strap-shaped leaves.
Spread of X-Disease
Movement of leafhoppers, and therefore X-disease, can also occur from infected sweet and sour cherry, particularly from trees on mazzard rootstock. Although the possibility of spread from peach to peach has been investigated many times, it appears to be of minor importance.
Identification of Chokecherries
Unlike black cherry and pin cherry, which grow like trees to 50 feet or more, chokecherries are shrubs up to 15 feet tall. They are usually found in clumps. The fruit of chokecherry, which is produced along a central stem, is black when mature and ripens before those of black cherry. The calyx cup on chokecherry fruit does not persist as it does on black cherry fruit. Pin cherry fruit are borne in clusters like sour cherry and in no way resemble those of chokecherry. Chokecherry leaves are wider and broader than black cherry or pin cherry leaves. Serrations along the margin of the leaves are more prominent and spreading than those of the other two species.
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|Data Source: Ohio State University Extension. Articles and resource may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide and it is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used.|