FACTORS AFFECTING INFECTION OF LOWBUSH BLUEBERRY BY ASCOSPORES OF MONILINIA-VACCINII-CORYMBOSI

Infection of lowbush blueberry (Vaccinium angustifolium) by ascospores of Monilinia vaccinii-corymbosi was examined in relation to mechanical and frost injury of the host, bud development, wetness duration, and temperatures of the wet period. Infection incidence of developing vegetative buds was low in the absence of injury but increased markedly when buds were gently pinched or exposed to freezing temperatures (-1.0 - -1.5-degrees-C) for one hour before inoculation. Ascospore germination on frosted buds was 42% compared to 2.5% on uninjured buds. Infection incidence of vegetative and truss buds increased with exposure to decreasing temperatures from 0 - -0.5-degrees-C to -1.5 - -2.0-degrees-C, but did not increase with increased exposure from 1 to 4 hours. Ascospore germination and infection incidence were highest when plants were inoculated immediately after exposure to frost and decreased daily to low levels after 4 days. The young tissues of developing buds were water-soaked following exposure to frost, but this symptom disappeared quickly and plants continued to develop normally. Some frost injury occurred at -1.5-degrees - -2.0-degrees-C. Infection incidence increased with advancing stage of development of vegetative and truss buds. Infection occurred within four hours of wetness at 6-18-degrees-C and after 10 hours at 2-degrees-C. The optimum temperature for infection was 14-degrees-C. These data are currently used in the Atlantic Provinces as a guide to time fungicide applications for effective control of ascospore infections.