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Fruit Tree Fungus #632762
Asked May 07, 2020, 9:09 PM EDT
Henrico County Virginia
Expert Response
Diagnosis: Black Knot (Dibotryon morbosum)
It seems the first two pictures are of the plum and the last picture may be of the pear, but it is difficult to see details due to the small size. I can see signs of the black knot fungus on the plum; however, I cannot see what is in the third pic (?pear). Black knot does not occur on pear.This is a common disease of cherries and plums. It can be difficult to control. Galled branches should be pruned out and burned or buried as soon as galls are noticed. Prune branches 4 inches below galls. If branches are pruned out the year the galls develop, the fungus will not be able to produce its spores on the galls. Galls are the color of the bark the first year and turn black with spore development in the second year. Wild cherries are very susceptible to the disease and often serve as an inoculum source for fruit trees growing near wooded areas. Refer to pp. 3-7 and 3-14 through 3-16 for information on fungicide efficacy and the spray schedule for stone fruit diseases in the Home Grounds and Animals Pest Management Guide (https://www.pubs.ext.vt.edu/456/456-018/456-018.html). There are plum cultivars available that are resistant to this disease and since this is such a common disease, should be considered for any new plantings.