Cankers are defined as localized regions of dead plant tissue, or necrosis, in the bark of stems or branches of trees. Several different species of fungi cause cankers. Some cankers develop slowly over a period of several years whereas others grow rapidly once a tree has been infected. Cankers often completely girdle the stem, killing the tree. They are serious diseases and difficult to control.

FUSARIUM CANKERS,
FUSARIUM SP.

Description
    Several species of Fusarium are known to cause cankers in black walnut in the Midwest and North Carolina. Trees in other States are also probably affected by the canker.

    Elongate cankers of various lengths usually occur on the lower portions of the main stems of young trees, near the ground line. However, cankers may also occur higher on the stem or on branches in the lower crown of young trees. Cankers first appear as breaks in the bark or as expanding sunken areas. Darkly stained, diseased wood can be found beneath the bark. An affected tree often produces sprouts near the canker or at the base of the stem. Sometimes tiny pinholes caused by an ambrosia beetle can be found within the cankered area.

Injury
    Affected trees show cankered, stained areas on the stems. An otherwise normal-looking tree that is producing many basal sprouts is commonly cankered. The primary injuries caused are wilting of leaves and dieback of the top. When the top has died, a sprout may take over and replace the lost tree, but several years of growth are lost.

Control
    Cut and remove diseased trees from the plantation. Prune dormant trees and burn or remove pruning debris from the area.

PERENNIAL TARGET CANKER,
NECTRIA GALLIGENA BRESS.

Description
    Perennial target canker, also known as Nectria canker, occurs on black walnut throughout its range, but seems to be more common in the Northeast and the southern Appalachians.

    Old cankers are easily recognized because of their typical target shape, caused by rings, each of which represents a year's growth of callous tissue around the infected area. Young cankers are not as easily recognized because overgrown callous tissue may hide the affected area. Tiny, red fruiting bodies of the Nectria fungus may be present around the diseased area.

Injury
    Cankers usually occur on the main stem of the tree, often at a point where a branch broke off and left an open wound. Nectria canker results in defects in the wood, stunting of growth, or death (if the canker becomes large enough to girdle the stem). Trees may also break at canker locations during high winds.

Control
    Cut infected trees and remove from the area, including other tree species that may also be affected: yellow birch, sassafras, paper birch, northern red oak, red maple, beech, and bigtooth aspen.