Peach canker is a fungus disease common on apricot, prune, plum, and sweet cherry trees as well as on peach trees. The disease is common in peach orchards and is a frequent cause of limb dying and death of peach trees. Other common names for peach canker are perennial canker and Valsa canker. The fungi that cause this disease enter the plant through wounds. Infection results in dead and weakened twigs and branches, and in reduced yields.
|Figure 1. Peach canker in a narrow-angled crotch. Gummy exudate is present.|
The first symptoms appear in early spring as gummy drops of sap around wounded bark. The diseased inner bark begins to break down, causing the cankered surface to appear depressed. Black specks, which are fungal spore producing bodies, appear on the bark surface or under the bark tissue. During wet periods spores ooze out of these fungal bodies in tiny orange or amber colored, curled strands.
During the summer, healthy bark (callus tissue) grows over the edges of the narrow, oval shaped cankers. In the fall, the fungus resumes growth, attacking and killing the new callus tissue. Over a period of years, a series of dead callus ridges form as the canker gets larger. Eventually, the canker may completely surround a branch. The portion of the branch beyond the canker then dies. Large amounts of gum are usually produced around cankered areas.
Peach canker is often confused with other problems which cause cankering and gumming. Among these are bacterial canker, insect borer injury and mechanical injury. When insects are involved, chewed-up wood dust is usually visible under the gum. Mechanical injury can often be verified by carefully reviewing recent operations in the area.
Peach canker is caused by the fungi, Cytospora leucostoma and Cytospora cincta. These fungi are weak pathogens and generally do not attack healthy, vigorous peach bark. Winter injury, insect damage, and mechanical injury are common types of wounds serving as entry points. The fungi survive the winter in cankers or in dead wood. During spring and summer, spores produced in the cankers are spread by wind and rain to wounds on the same or nearby trees. The spores are not blown over long distances in the wind. Infection and canker development depend on temperature and the species of fungus involved. Cytospora cincta is favored by lower temperatures than Cytospora leucostoma. Because of the manner of infection and development of this disease, no single control measure is adequate. Most known control methods act indirectly by reducing points of entry or by reducing the level of inoculum. Fungicides are generally ineffective for controlling this disease.
Control can be facilitated by following these guidelines:
|Figure 2. Peach canker.|
- Prune young trees carefully to avoid weak, narrow-angled crotches. Narrow-angled crotches are frequent sites of breakage and winter injury.
- Delay pruning until early spring. This promotes quick healing. Remove cankered branches and dead wood while pruning. Do not leave protruding pruning stubs. Cut flush to the next larger branch.
- Eradicate cankers and remove badly cankered limbs, branches or trees. Burn or remove all cankered limbs soon after pruning. These limbs or branches serve as a reservoir for the disease causing fungi. Sanitation is critical, especially during the early life of the orchard.
- Do not plant new peach trees near established trees with canker.
- Avoid mechanical and insect injury.
- Promote vigorous, healthy peach trees with proper fertilization, pruning, and water.
- Do not over-fertilize late in the season. Winter injury is more common on these trees because winter hardening is delayed.
- White latex paint applied to the southwest side of trunks and lower scaffold branches may help avoid cold injury.
- Maintain a good control program for other diseases and insect pests, especially borers.
For the most current spray recommendations, commercial growers are referred to Bulletin 506, Midwest Fruit Pest Management Guide, and backyard growers are referred to Bulletin 780, Controlling Diseases and Insects in Home Fruit Plantings. These publications can be obtained from your county Extension office or the CFAES Publications online bookstore at estore.osu-extension.org.