Eastern comma larvae (Polygonia comma) were found to be a minor hop pest in the northeastern U.S.

But this is changing. According the U.S. Hops Association, hop production in non-traditional regions, such as the Northeastern U.S., now accounts for more than two percent of the total hop acreage in the country.

However, hops aren’t the only thing making a comeback — so are hop pests. Dr. Lily Calderwood, a researcher at the University of Vermont, has observed as much as 80-90% yield loss in northeastern hop yards due to arthropod pests.

Calderwood and a team of researchers decided to step in and try to help farmers manage pests by providing a comprehensive assessment of hop pests and how to manage them. Their results are published in an open access article in the Journal of Integrated Pest Management.

In the Northeast, commercial hop production had been in decline since 1860, and the decline was accelerated in the early 1900s by both prohibition and hop downy mildew, a fungus-like disease that infects hops. However, over the past five years, the crop has started to make a comeback, and many local breweries are eager to use them.

“With the increased interest in growing hops, arthropod pests became prevalent,” said Calderwood. “Locally sourced hops are in high demand from brewers, and the current regional hop acreage cannot provide enough hops at high enough yield and quality to meet the demand. This is due in part from both arthropod and disease pest pressure.”

Over the course of three growing seasons, the team observed seven farms growing commercially available hops of different varieties. They documented the pests present, the predators of pests present, the phenology of the insects, and the plant symptoms of infestation. They also provide management options for each of the pests.

The researchers were surprised by two discoveries. First, the two main pest of hops — the twospotted spider mite (Tetranychus urticae) and the hop aphid (Phorodon humuli) — might not require insecticides to be controlled. And second, insecticides might actually cause more harm than good.

“Natural enemy populations can actually manage twospotted spider mites and hop aphids,” said Calderwood. “We no longer spray any insecticide in our research hop yard for these pests that are typically economically damaging in other hop-growing regions.”

In two of the hop yards, the researchers found that insecticides “kill natural enemies and increase the risk of a twospotted spider mite outbreak.”

A complete breakdown of the pests, predators, and suggested management tactics can be found in the open-access article “Survey of Northeastern Hop Arthropod Pests and Their Natural Enemies.”