Effect of orchard cover crop on incidence of low-temperature-basidiomycete rot of stored Spartan Apples

Abstract

Apples cv. Spartan from the same orchard block in Kelowna, British Columbia, were stored in a controlled atmosphere storage facility for seven to eight months each year for a period of four years from 1989 to 1993 to study the effect of nitrogen fertilization rate and orchard cover crop on the incidence of low-temperature-basidiomycete (LTB) rot. The effect of adding orchard floor litter from the cover crop was studied during the last two years of the study. Rate of nitrogen fertilization did not affect disease incidence, but cover crop influenced LTB rot in apples stored with and without orchard floor litter. White clover litter placed in apple bags from the treatment of white clover with a clean strip on the tree row resulted in 12.8% LTB rot and was significantly higher than the mixed grass treatments. The effect was not as clear for apples stored without the addition of litter, although apples from the white clover cover had a higher incidence of LTB rot than apples from the clean orchard cover. Sterilizing the orchard litter by autoclaving reduced the incidence of LTB rot compared with nonautoclaved litter, and apples stored without litter had an even lower incidence of LTB rot. Isolations from symptomatic fruit in 1992 showed that 86% of the isolates were pathogenic and caused LTB rot. Spartan apples were infected early during fruit development, because 17.2% of the apples were infected by 23 June in 1993. In the orchard, Spartlett pear was more susceptible to LTB infection than Spartan apple. The use of cover crop management for reducing the incidence of LTB rot is discussed. Key words: Coprinus rot, postharvest, storage, control, pest management