Hop Powdery Mildew Control Through Alteration of Spring Pruning Practices

Area of Science:

• Plant Pathology
• Horticultural Science
• Agronomy

Background:

• Powdery mildew, caused by Podosphaera macularis, significantly threatens hop production in the Pacific Northwest, impacting yield and quality.
• Early-season pruning is a standard horticultural practice in hop cultivation.

Purpose of the Study:

• To quantify the impact of pruning timing and method on hop powdery mildew development.
• To assess the effects of pruning on hop cone yield and quality factors.

Main Methods:

• A 3-year study in a commercial hop yard evaluated delayed pruning (4 weeks) versus standard timing.
• Compared mechanical pruning with chemical desiccant pruning.
• Monitored disease incidence on leaves and cones, yield, bittering-acid levels, and cone color.

Main Results:

• A 4-week delay in pruning reduced leaf powdery mildew from 46% to 10% and cone incidence from 9% to 1%, with seasonal variations.
• Chemical pruning showed a slight but significant reduction in cone powdery mildew compared to mechanical pruning.
• Pruning treatments did not negatively affect cone yield, bittering-acid levels, or color over the study period.

Conclusions:

• Delayed pruning is an effective, low-cost strategy to manage hop powdery mildew and reduce early-season fungicide applications.
• This practice can be integrated into hop production without compromising yield or cone quality.