Managing hop stunt viroid

Hop stunt viroid is a serious disease you don’t want to get established in your hop yard.

Hop stunt viroid (HSVd) is a serious disease of hops that can cut yields by up to 65 percent and impact quality by reducing the percentages of alpha acids in the cones. Michigan State University Extension suggests you take advantage of a useful fact sheet, Practical Aspects of Managing Hop Stunt Viroid, developed by the National Clean Plant Network for Hops.

Keeping this disease out of your hop yard by using planting material certified to be free of HSVd is the best line of defense. Purchase your hop plants or rhizomes from a reputable source where plants have been propagated from virus-indexed stock. The primary means by which this disease is spread is by propagation from infected plants. Unintentional propagation from infected root pieces can and does occur, since it may take three to five growing seasons before obvious symptoms of the disease appear. Not all hop cultivars show symptoms equally.

Once established in a hop yard, HSVd is spread easily by mechanical means such as mowing, mechanical leaf stripping and cutting tools. Researchers are evaluating the best methods to prevent the spread of HSVd within a hop planting. Meanwhile, here are some suggestions from the fact sheet:

  • Using contact herbicides to hold back vigorous new annual growth in spring until the proper training date for that variety and removing weak shoots in the spring is preferable to the use of mechanical mowers that may transmit the viroid.
  • Removing basal vegetation later in the season by chemical rather than mechanical means also reduces the risk of transmission.
  • Thorough washing of farm equipment to remove plant residue and sap should reduce the likelihood of transmission between yards.
  • Work a known infected hop yard last.
  • Treating knives and cutting tools with a disinfectant solution such as 10 percent bleach solution for 10 minutes may reduce transmission, but results have been inconsistent.

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