"Gummosis" and "canker" are both terms used to describe various bacterial or fungal diseases that cause oozing, sunken lesions on trunks or limbs of afflicted trees and shrubs. The problem is most commonly seen on fruit trees, and often gets its start when the disease organism enters through a wound or borer entry hole. Wounds are often caused by weed whips or lawn mowers; trunk sunburn may also damage the bark and allow entry. Keeping the plant too wet makes it easier for bacteria or fungi to establish themselves.
To prevent the problem, avoid overwatering and take care not to injure plants. Protect young trees from sun scald by wrapping the trunks loosely in burlap. If the plant is generally healthy, it will usually seal off the cankers. If the canker appears on a small limb, prune it out well below the canker; disinfect tools between cuts.
There is no chemical control.