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• Hop powdery mildew is a high-risk disease that demands timely, aggressive management: Yield losses can reach 50–80% under moderate to high pressure, especially from bloom through cone set, making disease timing, cultivar susceptibility, and pressure monitoring critical for protecting cone quality and yield.
• Integrated IPM programs outperform single-tool approaches: Combining biologicals and conventional chemistries, rather than relying on a single product, improves efficacy, reduces resistance risk, and allows growers to balance cost, sustainability goals, and disease control throughout the season.
• Essential oil–based fungicides enhance performance and sustainability in powdery mildew control: Field trials show that thyme oil–based PathoCURB, when tank-mixed or rotated with standard fungicides, can improve cone protection, reduce disease incidence, lower input rates, and extend the useful life of conventional chemistries, making it a strong fit for long-term hop IPM programs.
Powdery mildew on hop is caused by the fungal species Podosphaera macularis. The disease is identifiable by a white, powdery substance coating the leaves and cones of the hop plant. As the fungus steals plant resources, infected hops can experience ripening issues, color loss, browning, shattering, reduced cone quality, and yield losses¹.
Why it Matters?
Yield loss can reach 50-80% under moderate to high pressure.
Fortunately, hop powdery mildew is well studied2,3,4 , and this information can be leveraged to develop effective treatment plans. Powdery mildew pressure fluctuates with environmental factors and can affect critical growth stages. Specifically, during growth periods of blooming through cone set, regular, often aggressive treatment is required to best protect the cones from powdery mildew damage.
Additionally, some hop cultivars are more susceptible to disease onset. Understanding the disease cycle, the level of pressure, and crop susceptibility will help growers time interventions more effectively.
There are several treatment options to consider, from biologicals to conventional chemistries. Input costs, disease pressure, and individual farming goals all play a role in choosing the correct approach to powdery mildew control. These goals may include:
Growers often begin with cost-effective sulfur-based applications in early growth stages and then transition to essential oil-based formulations or conventional chemistries as disease pressure increases throughout the season. Based on these considerations, an integrated pest management (IPM) program should be developed to achieve the most effective control of powdery mildew.
It is important to note that standard chemistries and biological formulations can complement one another in an IPM program, given that label restrictions and local regulations are followed. When choosing which biologicals to include, essential oil–based biopesticides are valuable tools for IPM programs. The naturally complex mixtures of volatile compounds found in essential oils provide multiple simultaneous modes of action, such as disrupting cells, inhibiting enzymes, and suppressing disease development.
Growers can take advantage of the benefits of essential oil-based formulations by combining or alternating them with conventional chemistries to:
Kemin Crop Technologies is an expert in the research and development of essential oil–based crop protection products, including a thyme oil–based fungicide-bactericide, PathoCURB. PathoCURB has been extensively field-tested across crops, diseases, and growing conditions, demonstrating strong efficacy against powdery mildew.
We partnered with the Washington Hop Commission to determine how our thyme oil-based fungicide, PathoCURB, performed against hop powdery mildew as a single tool and when added to an IPM program across three trials conducted in 20226, 20247, and 20258
In the first two trial years, PathoCURB was applied every 2 weeks at 1%, and helped reduce powdery mildew incidence by up to 50% under moderate-to-high disease pressure6,7. However, a single-product program can be costly and labor-intensive, so an additional trial was conducted in 2025 to evaluate the product's performance in two standard rotation programs:
The 2025 trial found that all disease treatment programs significantly reduced powdery mildew incidence compared with untreated plots. The plants treated with the tank mix of PathoCURB and Fluopyram/tebuconazole had significantly less powdery mildew on their cones than in the grower's standard rotation8 – ultimately protecting the grower's yield.
Pairing PathoCURB with conventional chemistries can improve cone protection while reducing input rates.
Essential oil-based formulations can enhance the effectiveness of standard fungicides
Tank mixes add valuable MoA diversity to extend chemical resistance development timelines
This approach fits well within hop IPM programs focused on sustainable powdery mildew management
How to adapt this learning to your commercial hop yard?
▪Understand how powdery mildew can impact your crop
▪Consider your goals and priorities to select appropriate inputs (organic production, cost control, resistance management, quality, etc.)
▪Stay ahead of the disease pressure cycle to mitigate damage
▪Choose your chemistries and rotation program with diverse MoAs in mind
▪Consider integrating an essential oil-based chemical into your IPM program for improved control.
Bridget is a technical services manager and trained microbiologist in Kemin Crop Technologies with over 10 years of experience working in Plant Pathology, Microbiology, and Genetics with a passion for aiding sustainable crop protection and nutrition.
