The primary arthropod pests of hops, Humulus lupulus L., in the Pacific Northwest are twospotted spider mite TSSM, Tetranychus urticae Koch, and the hop aphid, Phorodon humuli (Schrank). We have played a major role in developing tools for growers to use in controlling these pests.

Two-spotted spider mite is a major pest of hops in the Yakima Valley, piercing leaf cells and extracting juices, causing leaf mottling and reducing production. TSSM has a life cycle of only about 8-12 days and may have as many as 20 generations in a single season, each female laying 60 to 120 of the whitish, spherical eggs in her life time. Adults are very small (0.5 mm long) and difficult to see with the unaided eye but their webbing and cast skins are evident on the underside of leaves.

The hop aphid overwinters in the egg stage on plum trees. In the spring after 2-3 generations winged aphids appear and migrate to the summer host, hops, where they can cause major damage, usually on young and yellow green leaves. The damaged leaves turn brown, curl downward and are brittle and easily broken. The commercial value of the crops is reduced as the quantity and quality of the beer brewing components are negatively affected by the damage induced by the hop aphid.

Our poster presentation details the work we have completed for pest control on hops.