Roundup

Spider mites drink up hops profits

With world markets afloat in the alpha acids that add flavoring, bittering, and foaminess to beer, Idaho hop growers have been unable to keep a head on profits. Under pressure from low prices, Idaho production has flattened 20 percent since 1991Ñto just 3,300 acres in Boundary and Canyon counties this year. All the loss has come from Canyon County, just west of Boise.

At Parma, UI hop entomologist Jim Barbour is looking for ways to head off further drainage of acreage. "Either costs have to come down or prices have to go upÑand the growers don't control the price," he says.

At anywhere from $170 to $550, pest control represents a significant portion of the $2,600 to $3,000 expense of producing an acre of hops. The insecticides that control the two-spotted spider mite, the number one pest in Idaho hops, soak up $100 to $300 in an average year. Untreated, spider mite numbers can reach 3,000 per leaf at the tops of hop plants, tinting the leaves and cones a menacing red and producing off-odors and off-flavors that render the cones unmarketable. Cones, the plant's female flowers, are the source of the alpha acids for which hops are primarily grown.

"Spider mites are here every year in every field, and our arsenal of treatment options is far from optimal," says Barbour.

Hop entomologist Jim Barbour samples the tops of 18-foot-tall hop plants.

To expand that arsenal, he is testing the effectiveness of three new-generation, lightweight, mite-smothering horticultural crop oils. Not only do the oils cost just $15 to $25 an acre, but they leave behind no toxic residues and allow immediate re-entry into fields.

The western predatory mite, a native beneficial insect, can keep spider mite populations in check until 90-degree-plus temperatures begin to double spider mite numbers as rapidly as every three days. Barbour is testing whether predatory mite releases, before and after different kinds of annual crown pruning, can give them an earlier and stronger start and extend their effectiveness.

He will also evaluate pest populations on the wild hop plants growing in ditch banks where old hop roots were once tossed. "The wild plants aren't totally decimated by pests," he says. "Are they not attractive to pests, are they nutritionally inadequate for their growth and development, or do they harbor more natural enemies?" The answers could point scientists to changes in production practices, or in cultivated hops themselves, that allow growers to rely more heavily on natural controls. --Marlene Fritz