Willow trees are a favorite among tree lovers for their dramatic, elegant appearance. The willow (salix) is often found along rivers and streams, but will grow well in almost any area. Willows thrive in full sunlight and adapt well to all types of soil; they are sometimes helpful in preventing soil erosion. The willow is prone to several diseases that damage the leaves, wood and, in severe cases; may cause the death of the tree.
Caused by the fungus Fusicladium saliciperdum, willow scab is one of the more serious diseases that affect willow trees. Damp, wet weather creates favorable conditions for the spread of this infection. Oddly-shaped brown spots appear on the leaf surface along the main veins and midribs. Spots turn olive green as spores begin to form. Younger leaves are especially prone to willow scab and may have spots all along the midribs and veins. Badly infected leaves will dry up and drop. The fungus will spread into the twig or young branch and dark cankers may develop which results in the die-back of branches and twigs. Treat willow scab with a copper fungicide; always follow manufactures instructions when using chemicals. Enlist preventative measures by pruning trees of dead twigs and branches, rake up all fallen leaves and diseased matter and burn.
Crown gall is a bacterium that causes tumors, often called galls, to form on the roots and stems and sometimes, the branches of willow trees. Small, round, light-colored knots appear on the root, slowly becoming larger and more numerous as the tree develops. They eventually will encircle and surround the infected area of the root or stem and will cause developmental problems. Leaves are discolored, die-back becomes prevalent and the growth of the tree is stunted. Crown gall also makes trees more susceptible to other diseases that can enter the rotting galls. There is no known treatment of crown gall. The best recourse is to remove and destroy willow trees that have been infected with crown gall.
Various species of the fungus cytospora cause cytospora canker to appear on willow trees.The fungus will attack trees or parts of the tree that are stressed or in a weakened condition. The fungus grows in the bark and wood and eventually damages the tree. Symptoms are yellow, black or brownish-orange discolored areas on the bark of the tree. Cankers, pimple-like black speckles, appear on the bark of the tree. The cankers produce spores, which under moist conditions, will leak from the cankers in long, orange, thread like tendrils. Wood and inner bark may appear to be reddish brown in color. Dead bark will remain attached to trees for years before falling off in pieces. Controlling cytospora canker is best done by maintaining the health of your tree. Wounds caused by lawn equipment leave your tree susceptible to canker. Once canker occurs, remove all infected branches and make clean even cuts on branches that have jagged edges. Clean fresh wounds by removing diseased area, in older wounds remove loose pieces of bark. Do not apply dressings to the wounds; allow them to dry out.