Comparison of Neonicotinoid Foliar and Seed Treatments for Management of Rice Water Weevil in Three Commercial Rice Varieties, 2016

The rice water weevil (RWW) is the most damaging insect pest in Louisiana rice. The objective of this experiment was to compare the efficacy of a neonicotinoid seed treatment and a neonicotinoid foliar treatment against RWW in a hybrid and two conventional varieties of rice. Field plots, 4.1 by 18 ft, 7 rows at 7 in spacing, were drill seeded at the LSU AgCenter H. Rouse Caffey Rice Research Station on 9 May. Each variety was seeded at its recommended rate, Gemini at 25 lbs/acre, CL161 at 50 lbs/acre, and Cheniere at 75 lbs/acre. Plots were fertilized with 120 lbs N per acre on 2 Jun, and flooded immediately after fertilization. Seeds were treated with CruiserMaxx at a rate of 7 fl oz per 100 lbs seed before seeding. Foliar applications of Belay were made on 1 Jun, one day before flooding. Belay was applied with a backpack sprayer at 15 GPA and 20 psi, with 8002 Teejet nozzle, and a 3.2-ft boom. There were nine total treatments. Treatments were factorial combinations of the three varieties and three insecticide treatments (CruiserMaxx seed treatment, Belay foliar treatment, and untreated). There were four replicates of each treatment arranged in a RCBD. Weather and soil conditions were normal for the test location. The procedure for counting RWW involves taking soil core samples using a soil coring tool, diameter 9.2 cm depth 7.6 cm, which allows equally sized samples of soil and rice roots to be collected. Subsequently the roots are rinsed through a mesh screen bucket. The screen bucket is placed in salt water and floating larvae and pupae are counted. Soil core samples were taken on two dates, 24 Jun and 6 Jul, 22 and 34 days after flooding respectively. On 24 Jun, three cores per plot were taken, and on 6 Jul, two cores per plot were taken. Yields from whole plots were collected. The average number of RWW larvae per plot, and the total yield per plot were used in analysis. Treatment differences were analyzed using SAS software PROC GLIMMIX, with block used as a random effect. Fixed effects were variety, insecticide, and the variety by insecticide interaction. Means were compared by Fisher’s LSD (P ≤ 0.05).

Results from the 24 Jun sampling date showed no significant effect of variety (F = 0.92, P=0.41) or variety by insecticide interaction on RWW (F = 2.48, P = 0.07). On the 6 Jul, sampling date there was no significant effect of variety (F = 0.26, P = 0.7748). However, there was a significant variety by insecticide interaction on RWW (F = 5.03, P < 0.01). The interaction arose from the lack of effect of insecticide on RWW in CL161, and the presence of this effect in the other two varieties. On both 24 Jun and 6 Jul, insecticide treatments had a significant effect on RWW densities (F = 7.94, P < 0.01; F = 18.49, P < 0.0001). Untreated plots were found to have significantly higher numbers of RWW. RWW densities did not differ among CruiserMaxx- and Belay-treated plots. Yield was significantly affected by variety (F = 75.97, P<0.0001). Yields of all ‘Gemini’ plots were significantly higher than yields of the other varieties. Yields were also significantly affected by insecticide treatment (F = 4.10, P=0.03). Cruiser-treated plots of ‘Gemini’ had significantly higher yields than untreated and Belay-treated plots. The interaction was not significant (F = 0.58, P = 0.68) (Table 1). This research was supported by industry gifts of pesticide from Valent and Syngenta.

Author notes