RELATIONSHIP BETWEEN FRUIT YIELD AND DAMAGE BY CODLING MOTH AND PLUM CURCULIO IN A BIOLOGICALLY-MANAGED APPLE ORCHARD

Fruit yield, codling moth (Cydia pomonella) damage, and plum curculio (Conotrachelus nenuphar) damage were monitored over an 8-year period i n a 0.5-ha, biologically-managed apple orchard in southwestern Michiga n. The relationship between yield and damage was examined for both of these pests. The orchard showed clear biennial bearing patterns of alt ernating high and low yields. A significant negative correlation was f ound for yield and percentage damage by codling moth but not for plum curculio damage. However, the estimated amount of fruit damaged by cod ling moth remained relatively stable over the period, indicating that changes in percentage damage depended on yield dynamics rather than ch anges in codling moth abundance. In contrast, the amount of fruit dama ged by plum curculio showed biennial fluctuations and a positive corre lation with yield, indicating that the population of this pest was cap able of responding with increased oviposition in years with greater fr uit yield. In addition, a comparison of codling moth fruit injury in y ears with and without the use of pheromone mating disruption showed no statistically significant reduction in damage as a result of using th is method, suggesting that the orchard may be too small or codling mot h populations too high for effective use of this management tactic.