Predicting Damage to Hop Cones by <i>Tetranychus urticae</i> (Acari: Tetranychidae)

Abstract Twospotted spider mite (Tetranychus urticae Koch) is a cosmopolitan pest of numerous plants, including hop (Humulus lupulus L.). The most costly damage from the on results infestation cones, which are harvested product, can render crops unsalable if cones become discolored. We analyzed 14 yr historical data 312 individual experimental plots in western Oregon to identify risk factors associated with visual T. urticae. Logistic regression models were fit estimate probability cone damage. predictive model was based urticae-days during mid-July harvest, correctly predicted occurrence and nonoccurrence 91 93% sets, respectively, Youden’s index. A second ratio predatory arthropods late season 92% sets 77% sets. abundance performed similarly when validated 23 commercial yards, whereas predator:prey relatively conservative yielded false-positive predictions 11 yards. Antecedents these explored quantified by structural equation modeling. simple path diagram constructed that conceptualizes invasion as dependent prior density leaves early spring summer, turn influences development mediate late-season pest. In summary, biological insights developed here provide guidance managers likelihood inform management both its important predators. This critically because formal economic threshold for does not exist current efforts may be mistimed influence crop probable. More broadly, this research suggests practices target fact predispose yards later outbreaks