Black Knot-Resistant Plum Varieties

Resistance

• American plum tree varieties appear to be more susceptible to black knot fungus than Japanese or European trees. Japanese plum trees tend to have the best resistance of all the plum trees. The cultivar President offers complete resistance to black knot, according to Ohio State University. An English tree, it was developed at the beginning of the 1900s by Rivers Nursery, in Hertfordshire, England. It produces a heavy crop of bluish-purple fruit.

Slightly Susceptible Trees

• The Shiro plum tree has only a slight bit of susceptibility to black knot. A Japanese plum tree, the Shiro depends on other Japanese plum types for pollination. The tree produces a yellow plum that is good for cooking and fresh eating. The Burbank plum -- a Japanese tree -- has considerable resistance to black knot. It produces a mottled yellow and red plum that is superior when eaten fresh.

Moderately Susceptible Trees

• The Europen plum tree Vanette has only moderate susceptibility to black knot. The tree bears deep purple sweet fruit. The Valor plum tree is self-pollinating and has only moderate susceptibility to the fungus. It produces large, deep purple fruit that have a bright yellow interior. A sweet plum, it is widely consumed fresh. A European plum tree, the Voyageur has moderate resistance to the fungus. The tree's fruit appears medium purple and moderately sized.

Prevention

• Plant only plum trees that have complete to moderate resistance to black knot. The gardener should always avoid planting a plum tree near other trees that may have black knot fungus. Use a fungicide to help prevent the tree from becoming infested with the black knot fungus. Applying a single lime-sulfur spray before the tree's buds open has been shown to help prevent black knot fungus, according to the Connecticut Agricultural Experiment Stataion.