Pioneer Plant-Tech, Inc.

Clean Matters

Hops are susceptible to numerous viruses, viroids, mildews, and other diseases, and an infection can cause dramatic drops in yields or even plant death.  Starting with clean, virus and disease free hops plants is a critical part of the process. We produce our hops for sale to New York, Vermont, Quebec, Ontario, and other Canadian provinces using this process. 

The Importance of Starting Clean

Perhaps the greatest danger to the Northeast's fledgling hops industry—and the individual farmers who invest in the significant start-up costs of hops production—is the prospect of disease.  Numerous viral, viroid, fungal, oomycete, and bacterial pathogens affect hops and can dramatically impact both the size and quality of yields.  In fact, the ‘Disease Management: Fungal & Bacterial Diseases” section of the Field Guide For Integrated Pest Management In Hops enumerates close to a dozen ‘major’ diseases which affect hops, as well as more than twenty additional ‘minor’ or less common conditions.  A few examples of conditions commonly transmitted through root and plant stock:

  • Hops Stunt Viroid.  Pathogen which impedes normal growth and can reduce hop yield by 60% or more. It was detected for the first time in the U.S. hop industry in 2004.  There was evidence that on-farm propagation of two different hop strains from diseased plants had resulted in large blocks of infected plants.  In the time since, the condition has been reported in locations as far away as Slovenia.
  • Carlaviruses. Viral conditions spread by infected plant stock as well as via insects and mechanical harvesting.  Some hops species are now resistant, but many critical strains can still be severely impacted in both yield volume as well as in reductions of the alpha acids and lupulin which measure hops quality.  Examples:
    •  Apple Mosaic Virus: Can reduce cone weight by 50%, and reduce alpha acids content
    • Hop Mosaic Virus:  Has been shown to reduce yield by 62% and alpha acids content by 18%.  Notably, the Chinook variety of hops is particularly susceptible to Hop Mosaic Virus. 
    • Hop Latent Virus:  Has been shown to reduce yield by 70% and alpha acids content by 44%
    • American Hop Latent Virus:  Has been shown to reduce yield by 14% and alpha acids content by 12%
  • Downey and powdery mildew (oomycetes).  Of particular concern in New York, where damp conditions encourage growth, these maladies are spread by contaminated planting stock as well as airborne/mechanically transmitted spores.  Infestations can result in yield loss of up to 100% (plant death and cone quality). Downey is the primary culprit in New York, as the powdery variety is less common.

Many factors play into a farmer’s ability to maintain a disease-free hops crop, but nothing is more important that starting with plants that are ‘clean,’ as each of the conditions described above can be transmitted through infected plant stock.  New York State authorities are extremely concerned about this aspect of the developing hops industry.  As summarized by Cornell University Cooperative Extension Hops Specialist Steve Miller:

The New York Farm Viability Institute recently provided emergency funding to help Cornell University and Cooperative Extension staff work with New York greenhouse propagators and potential importers ensuring that hop growers will have access to clean stock for planting. Hops are grown as perennials and planted with asexually propagated stock, similar to apples and grapes. It is critical that this stock be clean and free of diseases that can cause an economic impact to the individual grower as well as the potential to spread to other hop farms in the state. . . . These diseases can have a major impact on the hops industry.

Significant attention has been devoted to the issue by industry groups and even the federal government. For starters, the Pacific Northwestern states (Washington, Oregon, and Idaho) have instituted a quarantine forbidding the importation of live hops from outside the region.  Moreover, on a national level, hops are one of six plants that have been incorporated into the federally-funded National Clean Plant Network, which maintains a core stock of certified disease free plants at the Clean Plant Center Northwest station at the University of Washington in Prosser, WA.  For a fee (and subject to extremely limited availability), hops growers can obtain clean plant samples for use as a starting point for the propagation of field ready plants. 

Please review Why Our Hops Are Different to learn about how we ensure that our hops plants are free from the pathogens that typically impact hops and ready for a clean start in your hop yard when they leave our doors.