Efficacy of Pyrethroid Foliar Application Against Rice Water Weevil, 2018

The rice water weevil (RWW) is the most destructive early-season pest of rice in the United States. Foliar applications of pyrethroid insecticides are used to control adult RWW to prevent oviposition. This study was conducted to evaluate the efficacy of two pyrethroid insecticides via foliar application against RWW. Small field plots (4.1 by 18 ft, 7 rows at 7-inch spacing) were drill-seeded at the LSU AgCenter H. Rouse Caffey Rice Research Station in Crowley, Louisiana (30°14′22.406″N, 92°20′46.195″W, 7 m asl) on 23 Mar. Seeds of the long-grain Clearfield variety ‘CL153’ were drill-planted at a seeding rate of 60 lbs/acre. After planting, field plots were surface irrigated as necessary to facilitate plant emergence. Nitrogen was applied in the form of urea at 120 lbs N/acre on 16 May and permanent flood was established the following day. Foliar applications of two rates of Fastac (AI: alpha-cypermethrin), two rates of Mustang Maxx (AI: zeta-cypermethrin), and an untreated check were made on 18 May (one day after flooding) and on 29 May (Table 1). The five treatments were arranged in a randomized block design with six replicates. Treatments were applied using a backpack sprayer at 10 gpa and 20 psi with Teejet TP11001 nozzles at 19-inch spacing. Densities of immature RWW were determined on 11 and 18 Jun using a metal core sampler with a diameter of 9.2 cm and a depth of 7.6 cm. At each sampling date, two root/soil core samples were taken from every plot where each core sample contained a minimum of one rice plant with intact roots. Core samples were processed by washing the soil and larvae from roots in sieve mesh buckets. Buckets were placed in basins of salt water solution and immature weevils were counted as they floated to the surface. The number of RWW larvae in two core samples from each plot was averaged to obtain an estimate of larval density in each plot. Densities of RWW larvae from two core sampling dates were analyzed separately using one-way ANOVA with insecticide treatment as a fixed effect and block as a random effect using PROC GLIMMIX in SAS. Means were separated using Tukey’s HSD.

Results showed no significant effect of insecticide treatment on RWW larval density from the 11 Jun core sampling. Similarly, there were no significant differences among insecticide treatments on RWW larval density from the 18 Jun core sampling (Table 1).

This research was supported by industry gifts of pesticides and research funding.