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Plant NameTypeDescription 
Armillaria root rotOrnamental PlumDiseaseArmillaria root rot is a fungal disease transmitted between plants by root contact. Armillaria is often found in newly cleared soils or ones which have been flooded. Symptoms typically include sudden or gradual slowing of growth, yellowish or undersized leaves, leaf drop, dieback of branches, or gumming (sticky, oozing sap). White thread-like masses of the fungus may be found beneath the bark near the crown of infected trees, and/or as shoestring-like rhizomorphs, which are dark strands of the fungus growing on or just beneath the soil surface. Honey-colored mushrooms often grow near the base of infected trees in the fall. Infected trees may also exhibit a dark black line in the infected area encircling the base of the plant. Armillaria-infected trees have damaged root systems and are more likely to fall in high winds. It may also make trees more susceptible to insect attack
Brown rotOrnamental PlumDiseaseBrown rot is a fungal disease which initially infects the flowers. The petals turn light brown, develop water-soaked spots and may have tan or grayish areas of fungal spores. Infected flowers often remain attached to the plant, spreading the disease to small twigs and branches. Infected twigs and branches are often observed in the summer as flagged, dead leaves and twigs. Infected branches develop cankers which may produce gumming (leaking sap) or may girdle and kill the branch. Most brown rot cankers develop with a dead twig at the center where the initial branch infection occurred. Fruit can also be infected, dry out, and hang in the tree. Tan or gray fungal spores can also be found on infected blossoms, fruit, or twig cankers. Ornamental and fruiting stone fruit trees are affected.
Crown gallOrnamental PlumDiseaseCrown gall is a bacterial infection that can attack through wounds to the lower trunk, crown, or larger roots. Susceptible plants first develop soft warty or spongy swellings on the crown or roots. These enlarge over time and may reach a diameter of several inches on mature trees. Young trees can be stunted and girdled, but older trees are seldom killed by the infection. Infected trees may be more susceptible to drought and winter injury and are often weakened at the site of the gall. The crown gall bacterium survives in the soil in plant tissues and is often spread by contaminated nursery stock or cultivation equipment.
Cytospora cankerOrnamental PlumDiseaseCytospora canker infects the bark and cambium (the growing layer beneath the bark), and may be found in the outer layers of wood. Cuts into newly infected areas often reveal a reddish discoloration in the inner bark. Leaves above the infection site droop and discolor and twigs die back, resulting in "flags" of dead material. Infected branches develop cankers which may display gumming (oozing sap), a dead twig at the center of the canker, pinhead-sized bumps on the bark, and a sunken area on the surface of the branch at the canker margin. Amber to orange-colored spores may be seen oozing from the pinhead-sized bumps. The canker may girdle and kill the branch or increase in length each year, resulting in a "perennial canker". This fungal disease often infects through injury sites.
Plum pocketsOrnamental PlumDiseasePlum pockets is caused by a fungal infection of the leaves, twigs, and small branches. The fungus overwinters on twigs or bud scales. Infection occurs on young plant parts in the spring. The affected plant parts are distorted and swollen, with leaves often developing a yellowish to reddish color and blister-like distortions. Fruits (if produced) are also affected, becoming swollen, spongy, and yellow to dark brown or black in color, then turning dry and hardened (mummified). Mummified fruits serve as another source of infection.
Shothole (Coryneum blight)Ornamental PlumDiseaseCoryneum blight is a fungal disease. Lesions on leaves are initially small, purplish, round to oval areas which expand into brown spots with light centers. The lesions are typically up to 1/4" in diameter. The infected spots on leaves often die and drop out in warm weather, giving leaves the characteristic "shothole" appearance of the disease. The fungus probably overwinters on the bark and in infected buds. Spores are easily spread by water.
Silver leafOrnamental PlumDiseaseSilver leaf is a fungal disease which attacks the shoots, branches, trunk, and roots. The fungus is usually a saprophyte living on dead plant tissues, but it can attack living plants through wounds such as those made by pruning, winter injury, and insect damage. Leaves of affected twigs turn silver to ashy in color. They may turn up at the edges. The leaf discoloration spreads rapidly over whole branches and eventually to the entire tree. Affected leaves drop and the branch declines and dies. After the branch or tree dies, the fungus produces flat, crust-like or projecting fruiting bodies on the dead wood. The fruiting bodies are usually pinkish to purplish on the underside.
VirusesOrnamental PlumDiseaseVirus diseases in prunes and plums cause many variable symptoms depending on the virus strain and the cultivar affected. For instance, tomato ringspot virus can cause failure of the graft union, ultimately killing trees. Trees infected with a virus may also show various symptoms of decline, collapse, or breakage, which may be confused with root rots or other disease problems. Virus disease transmission is specific for each virus. Insects, nematodes, and grafting are possible modes of transmission.
Hop aphidOrnamental PlumInsectHop aphids are yellowish to bluish-green in color. They feed on plum, prune, cherry, and other hosts in the winter, then migrate to a summer host such as hops or sunflower. Some aphids remain on the winter host all year round. Their feeding causes leaves to roll. Typically, they are found on the underside of plum leaves, or inside the rolled leaves. Heavily infested plants may drop leaves, resulting in severe defoliation.
Leaf curl plum aphidOrnamental PlumInsectThe leaf curl plum aphid is typically pale green to yellow in color during the summer and darker green to brown later in the year. The aphids overwinter as eggs on plum and prune trees, then may migrate to various summer hosts or remain on the plum trees. Feeding by the leaf curl plum aphid causes severe curling of leaves on plum.
Peachtree borerOrnamental PlumInsectThe western peachtree borer is the larvae of a clear-winged moth. Adult moths are blue-black, about 1" across, have mostly transparent wings, and appear somewhat wasp-like. They are attracted to bark injuries. The larvae are white to yellowish with brown heads and often mine around the roots, in the trunk at ground level, or higher on the trunk. Mined trees often have gumming (sap leakage) and large amounts of a sawdust-like material present at the entrance holes. Mining can weaken and kill large branches and entire trees by girdling them.
Pear slugOrnamental PlumInsectPear slugs, or pear sawflies, are insect larvae which resemble a small greenish or black slug. They are typically 1/4" to 1/2" long, tadpole-shaped, and produce large amounts of slime on their bodies. The adult sawfly is a small, dark, wasp-like insect which is usually about 1/4" long. The larvae feed on the leaves of plum, cherry, and pear trees. Leaves are typically skeletonized (the upper layers of the leaf are eaten away, leaving only the veins and the lower leaf surface). Heavily damaged leaves may drop. The pear slug can be found from mid- to late spring and again in late summer. There are two generations per year.
ScalesOrnamental PlumInsectVarious species of scales attack ornamental plum trees. Depending on species, scales may be found on the upper or lower surfaces of leaves, or on twigs and branches. Symptoms of scale infestations may include yellowing and/or wilting of leaves on affected plant parts as well as the presence of honeydew, a sweet, sticky material produced by some species of scales. The honeydew may become covered with a dark growth of sooty mold. Scale insects are typically yellowish to dark brown or gray in color and rounded or oval in shape. They are generally 1/8" long or less.