Influence of Nitrogen Fertilizer Rate on Hop Looper

• Published in: Journal of economic entomology 2018-09, Vol.111 (5), p.2499-2502
• Main Authors: Iskra, A. E, Woods, J. L, Gent, D. H
• Format: Article
• Language: English
• Subjects: Abundance; Agricultural chemicals; Ammonia; Annual variations; Cones; Crop damage; Data processing; Defoliation; fertilizer; Fertilizers; Humulus lupulus; Hypena humili; Hypena humuli; integrated pest management; Larvae; Leaves; Nitrogen; Nitrogen fertilizers; Plants (Organisms); SHORT COMMUNICATION
• ISSN: 0022-0493; 1938-291X
• DOI: 10.1093/jee/toy229

Hop looper, Hypena humuli Harris, can cause substantial defoliation and crop damage by feeding on hop leaves and cones. A 4-yr field study conducted in western Oregon evaluated the abundance of hop looper larvae and associated defoliation of leaves on plants fertilized with nitrogen rates ranging from 44.8 to 269 kg/ha. There was annual variation in abundance of hop looper and defoliation, with a tendency for increasing nitrogen rate to increase both abundance of hop looper and defoliation. A mixed model analysis with data combined from 2014 to 2017 found that abundance of hop looper was linearly related to nitrogen fertilizer rate, with a 2.5 increase in hop looper-days per kilogram of nitrogen fertilizer applied. Similarly, based on data from 2015 to 2017, defoliation associated with hop looper increased 0.031 percent with each kilogram of nitrogen fertilizer applied.Therefore, avoiding unduly high rates of nitrogen fertilizer may reduce the abundance and defoliation caused by hop looper. Further studies are needed to understand the mechanisms associated with nitrogen stimulation of hop looper.