Flowering or ornamental plum trees are attractive yard trees in spring due to the profusion of fragrant blossoms. However, the trees are short lived and prone to a wide array of diseases and insect pests. Gardeners should prune annually to promote air circulation and remove dead growth. They should also learn to identify the major diseases that affect these trees.
Caused by the fungi Verticillium albo-atrum and Verticillium dahliae, verticillium wilt can kill flowering plum trees. Symptoms of this disease include yellowing or browning of leaves, reduced growth, wilting of leaves (often only on one side of the tree) and leaf curling or drying up. Gardeners cannot cure this disease with fungicide, but may control it by fumigating the soil. Before attempting to treat for verticillium wilt, contact a plant diagnostic laboratory (often found at state universities) about obtaining a test confirming its presence.
Leaf spot occurs when a flowering plum gets a fungal infection. Although this disease won't kill the plum tree, it does affect the tree's appearance. Homeowners can treat leaf spot with fungicides. Affected leaves display dark brown spots and yellow or tan blotches. The leaves can fall prematurely. Since the fungus remains in infected leaves and can get into the ground, rake up fallen leaves frequently to prevent the spread of disease.
The United States Forest Service notes that several insect pests can harm a flowering plum tree. Aphids, borers, scales, mealy bugs and tent caterpillars are the major pests that prey on this tree, but are by no means the only ones. Gardeners can treat these pests with insecticides or horticultural oils. The University of Minnesota maintains a database of pests infecting flowering trees that can help gardeners identify insects they find on their flowering plum (see Resources).
Most commonly occurring on ornamental plum and cherry trees in the northeastern United States, black knot is caused by the fungus Apiosporina morbosa. During winter, gardeners can observe black growths on the branches of the trees. The knots grow larger each year; those found on the main trunk can kill the tree. Gardeners can manage this disease by pruning out infected limbs and spraying with fungicides containing chlorothalonil or mancozeb.