See:
Peach (Prunus persica) - Wood Decay
Cause Most fungi that cause wood decay of stone fruit trees are those that produce mushrooms and conks, which are the bodies that produce spores. The spores are forcibly discharged from the mushrooms or conks, and usually are disseminated by air currents. Wood decay fungi enter trees primarily through wounds that expose sapwood or heartwood. Injuries from improper pruning (large stubs and horizontal cuts), sunburn, or damage from cultivating equipment can expose susceptible wood. Affected branches decay while the fungus continues to grow out in either direction from the original wound. Mushrooms develop after extensive colonization of the wood after conducive environmental conditions.
Wood decay is generally observed in older trees after extensive fungal colonization, but it also occurs in young trees. Decay fungi frequently function as secondary invaders following a succession of microorganisms, including bacteria, yeasts, and other fungi. Decay in a single tree may be caused by more than one fungal species.
Symptoms Wood decay leads to limb breakage, uprooted trees, trees broken at the soil line during windstorms or decreased tree vigor, and dieback. Infected wood is a different color than sound wood. White rots cause moist, soft, or spongy wood that is of a lighter color that sound wood. Brown rots of wood are brown, dry, and crumbly, with longitudinal and transverse cracks.
This means pruning out the affected branches will help prevent further spread. Prune until there is no evidence of discolored wood; don't leave prunings in the orchard, as the infected wood can eventually result in spread of the fungus.
Chemical control
- Prevent wood decay by using practices that promote tree growth and vigor while minimizing injuries that expose wood.
- Irrigation water, especially from sprinklers, should not wet the trunks.
- Cultivation and mowing equipment should not injure the roots, crown, or lower trunk.
- Make pruning cuts adjacent to, but not into, the supporting branch; prune when the branches are small, to enhance callus formation and wound healing.
- Tree paints for protecting wounds must provide complete coverage and maintain an intact layer to be useful. Sealants often crack and expose unprotected wood to decay fungi.
Reference Adaskaveg, J.E. and Ogawa, J.M. 1990. Wood decay pathology of fruit and nut trees in California. Plant Disease 74:341-352.