Major Diseases

Chestnut blight

The symptoms on Chinese chestnuts are cankered areas on the bark of a branch or the trunk. New cankers show sunken or swollen areas of bark; later, the bark may split and the foliage may wilt.

Good cultural practices and resistant varieties are the best means of control. Keep the trees growing with normal vigor and prune out cankered branches.

Pecan scab

Pecan nut husks infected with pecan scab.

Scab is a major disease on several southern pecan varieties, but northern pecan varieties, hickories, and hicans are usually not severely attacked.

Symptoms of scab are round or irregular olive-brown to black spots on leaves and young twigs and small, dark, circular spots on the husks of the plants (see image).

For home plantings, control with good sanitation. Rake up and burn or haul away all hickory, pecan, and hican leaves, shucks, and dead twigs. Where scab, leaf blotch, leaf scorch, spot anthracnose, anthracnose, or other fungus leaf spots are serious, apply 4 to 6 sprays 10 to 14 days apart. Start when the buds begin to open. Suggested fungicides include benomyl, maneb, mancozeb, and dodine. Follow label directions.

Walnut Anthracnose

Black walnut tree defoliated in late summer by anthracnose infection of the leaves.

Anthracnose is the most serious disease of black walnuts, although Persian walnuts are resistant to it. Anthracnose attacks leaves, nuts, and new shoots. Wet weather during late spring and early summer increases the severity of the infection. Severe infection causes leaves to drop prematurely, sometimes partially defoliating the trees by midsummer (see image).

Starting in May or June, small, dark spots appear on the leaves. These spots enlarge and may merge to form dead areas. Tiny, sunken, dark spots develop on the husks of the nuts. Husk infection early in the summer may cause the nuts to drop prematurely or to be improperly filled. Defoliation of the trees may also result in improperly filled nuts with dark kernels.

Sanitation and using the more resistant varieties are suggested for control. Each spring, rake up and burn or haul away all walnut leaves. The varieties in the suggested list show resistance to anthracnose.

Where anthracnose, yellow leaf blotch, and other fungus leaf spots and blights are serious, start spraying when the leaves begin to unfold and continue at 2-week intervals 3 or 4 times. Suggested fungicides include benomyl, dodine, maneb, and mancozeb.

Walnut blight

Persian walnuts are more susceptible than black walnuts to this bacterial disease. Blight attacks leaves, bark, shoots, and nuts. Infections on new shoots do not grow into older wood, so trees are not killed, but the nuts can be severely damaged and fail to fill properly. Nuts may be infected anytime during the growing season. First symptoms are small, water soaked spots on the nuts, leaves, or shoots. These spots enlarge and become dark and sunken.

Use fixed copper (50 to 55 percent copper) at the rate of 4 pounds per 100 gallons of water (3 level tablespoons per gallon). Spray 3 times: at the beginning and completion of flowering and at nut set.

Walnut bunch disease

Bunch disease affects black walnuts, pecans, and hickories and is especially serious on butternuts, Japanese heartnuts, and hybrids of butternuts and Japanese heartnuts. The causative organism and the method of transmission are not known, but some scientists suspect that a virus or a mycoplasma is involved.

Lateral (side) buds have a tendency to grow rather than remain dormant. This produces a "witch's broom" type of growth on the infected branches, characterized by bushy, closely spaced lateral shoots with undersized leaves. Upright, suckerlike shoots form on the trunks and main branches.

Infected branches frequently start growth earlier than normal in the spring and grow longer into the fall. This late fall growth retards normal cold-hardiness development, and the tips of infected branches are winterkilled. Branches infected with bunch disease do not produce normal crops of nuts.

For control, cut out the infected branches, making the cut well below the infected area. If the disease continues to spread into other branches, remove the entire tree.

Trade Names of Common Pesticides

Common Name  Trade Name
Bacillus thuringensis Dipel, Thuricide, many others
 Benomyl  Benlate, Topsin M
 Carbaryl  Sevin
 Dodine  Cyprex
 Mancozeb  Dithane M-45, Manzate 200
 Maneb  Manzate, Dithane M-22


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