Hops - Powdery Mildew Management

February 23, 1998

TO: Washington Hop Producers

FROM: Ann George

RE: Recommendations for Hop Powdery Mildew Management

At their February 11 meeting the Washington Hop Commission appointed a subcommittee of growers, representing each local growing area of the Yakima Valley, to meet and develop a set of recommendations for "Best Management Practices" for hop powdery mildew prior to the 1998 growing season. The subcommittee met today, and prepared the following recommendations.

Powdery Mildew Control will be expensive. Powdery Mildew is more expensive. Full cooperation of all Yakima Valley hop producers is necessary!

Recommendation for Idle Yards:

  1. Take them out! Remove crowns and aggressively control volunteers.

  2. Burn the roots.

Recommendation for ALL PLANTED ACREAGE (strung or unstrung):

  1. The most important time period is emergence to training. Timing is critical! If we can't control it during this time period, the remainder of the season will be disastrous! This is the cheapest and most effective time to spray. 100% of Yakima Valley planted hop acreage (strung or unstrung) must be treated during this time period!

    • Vigorous mechanical pruning - scratch this year, and begin to hill yards in order to implement crown pruning (cutting) next year.

    • Disc and cross-disc where possible.

    • Incorporate trash and residues into the soil.

    • Chemical burnback or flaming to eliminate all growth.

    A recommended regimen for all varieties (regardless of whether they are anticipated to be susceptible or tolerant to powdery mildew) includes: It may be possible to delay the first fungicide application with early mechanical pruning or flaming. Continue spraying every 7 to 10 days until your normal training schedule requires burnback.

    If you see flag shoots at any time? Burn down with chemical desiccant OR Cut off flag shoots by hand with a knife, as far below ground as possible; bag cuttings and remove them from the yard. Burn or bury infected cuttings. At the normal time for your training schedule, burn back 100% of the foliage.

    Upon re-emergence of shoots for training, resume fungicide treatments on a regular schedule (every 7-10 days, or as allowed on the approved product label). Continue to use sulfur and available biocontrol options for resistance management (provide an alternative mode of action to control "escapes" that can start to develop resistant populations).

    At training time there should be no powdery mildew present in a yard. If infection is present, burn back chemically and start over. If the subsequent regrowth is infected, this yard is probably not economic to produce!


  2. Aggressively rogue off-types from yards, and kill wild hops on ditchbanks, old hop land converted to other crops, etc. Talk to your neighbors. Discuss the issue with public rights-of-way managers. Dig out and kill these hops.


  3. Hilling - begin to build up hills to prepare yards for crown pruning next year and beyond.


  4. Flag shoots - Desiccate or prune immediately.


  5. Don't treat "tolerant" varieties any differently than "susceptible" varieties.

    We may have other disease strains that were not fully dispersed throughout the Yakima Valley last season, capable of overcoming resistance genes.

    Environmental conditions may not allow resistance genes to be fully expressed.

    "Off types" in yards may contribute significantly to the airborne spore load.

    (NOTE: Nugget has the R6 resistance gene. Germany has powdery mildew strains that have overcome the R6 gene, and Nugget is considered to be highly susceptible to powdery mildew there).


  6. Treat baby hops the same way as mature hops.


  7. When vines are high enough (June)?basal burnback and strip lower leaves to the 3-4 foot level.