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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #357190

Title: Influence of nitrogen fertilizer rate on hop looper

item ISKRA, ANNE - Oregon State University
item WOODS, JOANNA - Oregon State University
item Gent, David - Dave

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2018
Publication Date: 9/26/2018
Citation: Iskra, A.E., Woods, J.L., Gent, D.H. 2018. Influence of nitrogen fertilizer rate on hop looper. Journal of Economic Entomology. 111(5):2499-2502.

Interpretive Summary: In this research, we evaluated the impact that nitrogen fertilization practices may have on an important pest of hop, the hop looper. Over a period of four years, plants received varying levels of nitrogen fertilizer spanning the range of fertilization that could be observed in commercial production and levels of the hop looper larvae and their associated feeding damage to the plant were quantified. There was a direct relationship between the amount of nitrogen applied and both the number of hop looper larvae on plants and the amount of defoliation. Moderation of nitrogen fertility could be a component of an integrated pest management system for hop looper.

Technical Abstract: Hop looper, Hypena humuli Harris, can cause substantial defoliation and crop damage by feeding on hop leaves and cones. A four year 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 looper-days per kg of nitrogen fertilizer applied. Similarly, based on data from 2015 to 2017, defoliation associated with hop looper increased 0.031 percent with each kg 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.