Annemiek Schilder of Michigan State University Extension, Department of Plant, Soil and Microbial Sciences, notes the recent humidity and rainy periods have created ideal conditions for leaf rust development. Schilder cautions growers to survey plants for orange pustules or small, yellow spots that begin in mid- to late summer.
“It generally has little impact on current-season yield, but may cause premature defoliation. Severe defoliation has the potential to reduce fruitfulness of new buds or winter hardiness of the canes,” she writes.
Management tips, and the life cycle of the bacteria are found here.
Source: Michigan State University Extension