PEACH CANKER INVESTIGATIONS: III. FURTHER NOTES ON INCIDENCE, CONTRIBUTING FACTORS, AND RELATED PHENOMENA

Abstract

The relative importance of the different sources of canker varies from year to year. Some, e.g., pruning wounds and injuries from verticilliosis, become less, while others, such as dead twigs and fruit pedicels, become more significant with time. Still others show no definite trends but fluctuate according to conditions.Leaf scars are vulnerable for a time after leaf fall, because of a temporary absence of wound periderm in the leaf base, but the development of cankers from leaf scar infection is determined by an infrequent coincidence of physiological and meteorological factors.Some insects such as the oriental fruit moth (Laspeyresia molesta Busck.), the shot-hole borer (Scolytus rugulosus Ratz.), and the peach borer (Synanthedon exitiosa Say.) can cause injuries which frequently become cankered afterwards. The lesser peach borer (Synanthedon pictipes G. & R.) is seldom a primary parasite but may stimulate necrotic processes through its destruction of callus in cankers. The peach is most susceptible to canker in the fall, and injuries such as pruning cuts made at that time are much more subject to infection than those made at any other time of the year. The incidence of peach canker and of winter injury can also be increased significantly by prolonging the period of open cultivation. At least three types of winter injury have been observed, all of which may give rise to serious cankers.From 75 to 85% of the open cankers of all ages overwintering on the tree remain active. There is also a tendency for cankers to become less active with increasing age. Surgical treatment of important cases is of considerable value.