GRANULATE CUTWORM (Feltia subterranea) CONTROL IN ALFALFA: INSECTICIDE EFFICACY COMPARISON AND ALFALFA GROWTH RESPONSE
Applied Research
Michael Rethwisch
Farm Advisor - Crop Production and Entomology
University of California Cooperative Extension
Blythe
Abstract
Granulate cutworms (Feltia subterranea) can sometimes be severe pests of alfalfa grown during the summer in the low desert areas of Arizona and California with their feeding keeping alfalfa from re-greening for several weeks after a cutting when cutworm populations are high. This situation was noted in late summer 2025 in several local alfalfa fields, allowing opportunity to compare efficacy of various insecticides and document crop growth response. Seven (7) insecticides, consisting primarily of pyrethroid insecticides registered on alfalfa hay, were applied late afternoon on September 15, 2025, using a battery powered backpack sprayer equipped with a boom with 4 T-Jet 8002VS nozzle tips. Plots were 25 ft. long x 14 ft. wide and treatments had four replications, with plot design being randomized complete block. Plots were sampled the early morning of September 17 (36 hours after application). Sampling consisted of locating the row of shed leaves from the previous raking/ baling operations that ran across each plot, and removing this debris/duff from a 1 foot wide x 1 meter long area by scratching the leaves away from the soil and from within crowns and soil cracks to uncover granulate cutworm caterpillars. Numbers of caterpillars in plots (1 such sample/plot) were counted and recorded. Treatment means were statistically analyzed to determine if significant differences existed. Isocycloseram (Plinazolin technology/Vertento®) at 2 oz./acre the best initial control, with 64.9% fewer cutworms compared with untreated alfalfa. This insecticide is not yet registered for usage on U.S. alfalfa. Of the registered insecticides evaluated, products containing the active ingredients lambda-cyhalothrin (Warrior® II, Besiege®) or beta-cyfluthrin (Baythroid® XL) resulted in fewest granulate cutworms, with these providing 37-40% fewer than collected from the untreated alfalfa plot samples. The alpha-cypermethrin products (Fastac® CS, Fastac® EC) resulted in a slight reduction on granulate cutworm (5-10%). Alfalfa regrowth was not correlated with initial insect control as only Besiege® treated plots had green regrowth at 7 days post treatment. This product contains both lambda-cyhalothrin and chlorantraniliprole as active ingredients, indicating the latter active ingredient was providing additional benefit than from just lambda-cyhalothrin (Warrior® II) by itself.
Poster has NOT been presented at any previous NACAA AM/PIC
This poster is being submitted for judging. It will be displayed at the AM/PIC if not selected as a State winner. The abstract will be published in the proceedings.
Click to view Poster
Authors: Michael Rethwisch, Katelyn Bush
-
Rethwisch, M. Farm Advisor - Crop Production and Entomology, University of California Cooperative Extension - Riverside County, California, 92225
-
Bush, K. Student Assistant , University of California Cooperative Extension - Riverside County, California, 92225-1649