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Plum Tree Fungus

By Tarah Damask ; Updated September 21, 2017
Plum trees are susceptible to fungus problems.

Your enjoyment of home garden plum trees is under a considerably dangerous threat by fungus. Fungal pathogens that invade your stone fruit tree have the capacity to cause severe cosmetic damage as well as severe decline. Avoid home orchard tree problems through careful maintenance for continued healthy fruit production and visual interest in your home landscape.


Vigorous, well-cared-for plum trees have a greater capacity for fighting off or resisting fungus problems than neglected trees, according to the West Virginia University Kearneysville. Grow plum trees in areas that offer full sunlight for optimal fruit yields and growth, according to the AgriLife Extension Texas A&M System. Sun exposure during morning hours is essential, as it aids in drying dew, which creates an ideal environment for the germination of fungal pathogens. Plum trees thrive in moist, well-drained soil; avoid waterlogged conditions that also contribute to fungal growth.


Black knot disease is a fungus problem associated with plum trees; it is caused by the fungal pathogen Apiosporina morbosa, according to the West Virginia University Kearneysville. Fungal pathogens spread sporadically on wind and water and make their appearance during heavy rain, landing on and infecting new growth. Infection reaches its peak during a temperature range of 55 to 75 degrees Fahrenheit and ends when the development of new growth reaches its completion, according to the Penn State University Department of Plant Pathology.


Black knot fungus disease attacks the woody parts of plum trees, including branches, twigs and trunks. During summer or spring, swollen growths that resemble cork-like warts grow on tree surfaces in an olive green hue that becomes black, as the name suggests. The cork-like texture hardens with these knots, or growths, measuring as small as 1 inch and as large as 1 foot, according to the Penn State University Department of Plant Pathology. Particularly when left untreated, the knots may continue developing, leading to the death of your plum tree.


Avoid planting highly susceptible trees and choose resistant options instead, when possible. Black rot fungus is also found on cherry, peach and apricot trees. Contact your local county extension agent to determine the most resistant options for other plants in your region. Avoid highly susceptible plum cultivars Stanley and Shropshire as well as Milton and Early Italian, which exhibit moderate susceptibility. Instead, opt for the resistant cultivar President, according to the Penn State University Department of Plant Pathology.


For control of fungus on plum trees, remove and destroy infected parts, including creating a radius of approximately 1 inch of healthy wood surrounding the removed knot. Remove wild stone fruit trees from an area within a 500-foot radius of infected trees to prevent further spread of disease, according to the Penn State University Department of Plant Pathology. For chemical control of black knot, apply a fungicide with the active ingredient thiophanate-methyl, according to the West Virginia University Kearneysville.


About the Author


Tarah Damask's writing career began in 2003 and includes experience as a fashion writer/editor for Neiman Marcus, short fiction publications in "North Texas Review," a self-published novel, band biographies, charter school curriculum and articles for various websites. Damask holds a Master of Arts in English and creative writing from the University of North Texas.