Evaluation of Insecticides Against Cochineal Insect on Prickly Pear Cactus, 2017

A greenhouse trial comparing the efficacy of insecticide treatments against Cochineal insect (CI) was conducted on prickly pear cactus in Salinas, CA. Ten replicates of each treatment were assigned to potted-pads, oblong to spatulate stems called cladodes of prickly pear cactus according to a randomized completely block design. The details on insecticide products and their rates are shown in Table 1. Broadcast-spray of insecticide treatments were applied on 19 Jun 2017. The insecticides were applied using CO₂-powered sprayer. The water volume used for the applications was 60 gal per acre and was applied at 30 psi. Dyne-Amic (surfactant) was added at 0.25% vol/vol to all the treatments.

The noninfested cactus cladodes were planted into 1-gal pots (one pad per pot) and irrigated twice a week for 2 min. To inoculate the cactus pads, pieces of pads with gravid CI females and eggs were collected from commercial field and were placed inside the pots, in contact with the newly planted cactus pads. These pads were infested with F1 crawlers, which developed into females in 6–8 wk in the greenhouse. Three 2 × 2 cm squares were drawn using a marker pen on each pad where no CI was present. When emergence of F2 crawlers peaked from those F1 females, insecticide spray was conducted. Number of settled crawlers within the squares were quantified before insecticide application. As time passed, the settled crawlers developed into 2–4 instars on the pads with white woolly mass on them. The number of CI nymphs on three squares was added per pad (replica) and total nymphs were square-root transformed to establish homogeneity of variance. Transformed CI nymphal data were subjected to ANOVA using the generalized linear model (PROC GLM) procedure in SAS (SAS Institute 2012).

Precount of CI nymphs was similar among all the treatments (Table 1). After 7 d of application (DAA), the number of nymphs settled was significantly lower in Sevin treatment than in untreated check or in other treatments. Two weeks later, number of CI nymphs was not significantly different among treatments (P < 0.05). At 28 d after application, all the insecticide-treated pads had significantly lower number of nymphs than in the untreated check. After 35 d of application, there was no significant difference in number of nymphs among insecticide treatments. Overall, all the insecticide treatments tested in the trial were effective. The number of developing nymphs on all pads declined as the quality of cactus pads started to deteriorate. Also, none of the insecticide treatments showed evidence of phytotoxicity.

This research was supported by a grant from 2017 IR4 Grant Program.