Predicting damage to hop cones by Tetranychus urticae (Acari: Tetranychidae)

Authors: WOODS, JOANNA - Oregon State University; ISKRA, ANNE - Oregon State University; Gent, David - Dave

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2021
Publication Date: 2/16/2021
Citation: Woods, J.L., Iskra, A.E., Gent, D.H. 2021. Predicting damage to hop cones by Tetranychus urticae (Acari: Tetranychidae). Environmental Entomology. 50(3):673-684. https://doi.org/10.1093/ee/nvab008.
DOI: https://doi.org/10.1093/ee/nvab008

Interpretive Summary: Twospotted spider mite is cosmopolitan pest of numerous plants world wide, including hop. On hop, the most serious damage from the pest occurs when spider mites feed directly on cones, diminishing their quality and potentially leading to loss of entire crops. We analyzed 14 years of historical data from 624 individual experimental plots in western Oregon to identified risk factors associated with damage to hop cones from spider mites. A statistical model was produced that correctly predicted occurrence and non-occurrence of cone damage from spider mites in 91% and 93% of data sets used. We validated the model in 23 commercial hop yards to ensure that the predictions were robust across a range of commercial production situations. The most predictive model correctly classified spider mite damage in 21 of the 23 yards. Using the same historical data, we also examined the risk factors and events that precede cone damage at harvest. This analysis indicated that spider mite invasion of hop cones is associated with prior occurrence of the pest on leaves in early spring and summer, which in turn influences the development of predatory arthropods that can mediate late season populations of the pest. In sum, the analyses and models developed here provide guidance to pest mangers on the likelihood of cone damage and can inform their management based on both abundance of the pest and its important predators. This is critically important because a formal economic threshold for spider mites on hop does not exist and current management may be mistimed. More broadly, this research suggests that current management practices that target spider mites early in the season may in fact predispose hop yards to later outbreaks of the pest, which tend to be the most damaging to the crop.

Technical Abstract: Twospotted spider mite is cosmopolitan pest of numerous plants world wide, including hop. On hop, the most serious damage from the pest occurs when spider mites feed directly on cones, diminishing their quality and potentially leading to loss of entire crops. We analyzed 14 years of historical data from 624 individual experimental plots in western Oregon to identified risk factors associated with damage to hop cones from spider mites. A statistical model was produced that correctly predicted occurrence and non-occurrence of cone damage from spider mites in 91% and 93% of data sets used. We validated the model in 23 commercial hop yards to ensure that the predictions were robust across a range of commercial production situations. The most predictive model correctly classified spider mite damage in 21 of the 23 yards. Using the same historical data, we also examined the risk factors and events that precede cone damage at harvest. This analysis indicated that spider mite invasion of hop cones is associated with prior occurrence of the pest on leaves in early spring and summer, which in turn influences the development of predatory arthropods that can mediate late season populations of the pest. In sum, the analyses and models developed here provide guidance to pest mangers on the likelihood of cone damage and can inform their management based on both abundance of the pest and its important predators. This is critically important because a formal economic threshold for spider mites on hop does not exist and current management may be mistimed. More broadly, this research suggests that current management practices that target spider mites early in the season may in fact predispose hop yards to later outbreaks of the pest, which tend to be the most damaging to the crop.