Evaluation of Insecticides for Western Tarnished Plant Bug Management in Central Coast Strawberry, 2016 *

A trial comparing the efficacy of insecticide treatments against WTPB was conducted in a first-year planting of the strawberry variety ‘San Andreas’ in Watsonville, CA. Four replicates of each treatment were assigned to six 50-ft long 52-in. bed (with two plant rows per bed) according to a randomized completely block design. The details on insecticide products, rates, and application dates are shown in Table 1 . First broadcast-spray of insecticide treatments was applied on 29 Jun 2016 followed by a second broadcast-spray application on 8 Jul 2016. The insecticides were applied using commercial tractor mounted sprayer. The water volume used for both the applications was 150 GPA and was applied at 140 psi. Dyne-Amic (surfactant) was added at 0.25% v/v to all treatments.

Beat-trays were used to sample insect populations. Twenty strawberry plants were sampled between 11 AM and 2 PM from a plot and the sampling consists of five strikes per plant with the lid of a Rubbermaid container (14.9 × 12.2 × 6.7 in. [deep]). Sampling was done a day before application then at 2 and 7 d after first application then 2. 7, 14, and 21 d after second application. The insect samples were bagged, transported to the laboratory, and stored in the freezer for later evaluation in the laboratory. The samples were evaluated for all adults and nymphs of WTPB, heteropteran predators (damsel bug, minute pirate bug, and bigeyed bug) and spiders. In addition, 60 fruits were randomly sampled from each plot on 2 Aug 2016 at 25 d after second insecticide application. The fruits were evaluated for WTPB injury or “catface”. The number of adults and nymphs of WTPB, heteropteran predators, and spiders were log-transformed (ln[ x  +1]) to establish homogeneity of variance. The proportion of strawberry fruits with catfacing injury was arcsine square root transformed. Transformed data were subjected to ANOVA using the generalized linear model (PROC GLM) procedure in SAS (SAS Institute 2012).

In the pre-count sample, WTPB adults were not significantly different among treatments ( Table 1 ). After 2 d of first application, number of WTPB adults collected in Rimon + Brigade and Actara + Danitol treatments was significantly lower than in untreated check (UTC) as well as lower rate of Avaunt, Beleaf, Rimon, and Rimon + Assail treatments. A week after first application, there was no significant difference among treatments. Two days after second application, a significantly lower number of WTPB adults was collected in both higher and lower rates of Avaunt, Actara + Danitol, Rimon, and Sequoia treatments than in UTC treatment. A week after the second application, a significantly lower number of adults was collected in Rimon + Brigade treatment than in UTC. At 14 d after the second application, higher rate of Avaunt, Actara + Danitol, Beleaf, Rimon, Rimon + Assail, Rimon + Brigade and Sequoia significantly suppressed adults than in UTC. At 21 d after the application, adults were significantly lower in Rimon, higher rate of Avaunt, Rimon + Assail, and Rimon + Brigade than in Sivanto.

Pre-count of WTPB nymphs was similar among all treatments ( Table 2 ). The number of nymphs captured was significantly lower in all the treatments than in UTC at 2 d after first application. The density of nymphs was especially low in higher rate of Avaunt and Rimon + Brigade. Similarly, a week later first application, nymphs were significantly lower in all the treatments than in UTC. Rimon + Brigade treatment had the significantly lowest WTPB density. Two days after the second application, nymphs were significantly lower in Actara + Danitol, Rimon, Rimon + Assail, Rimon + Brigade, and Sequoia treatments than in UTC as well as lower rate of Avaunt treatments. At 7 d after second application, Rimon + Assail, Rimon + Brigade, Beleaf, and Sequoia had significantly lower number of nymphs than in UTC as well as lower rate of Avaunt, and Sivanto. A week later, all the treatments except lower rate of Avaunt suppressed nymphs compared with UTC. At 21 d after the second application, there was no significant difference in the number of nymphs collected among treatments.

The number of predatory bugs (damsel bug, minute pirate bug and bigeyed bug) was significantly lower in Actara + Danitol than in UTC. Also, number of nymphs was significantly lower in Rimon + Brigade than in Rimon alone and Sivanto treatments ( Table 3 ). Spider populations were significantly lower in Rimon + Brigade than in UTC as well as other treatments except Actara + Danitol.

Fruit evaluation show that number of fruits with catface injury was significantly lower in all the insecticide treatments when compared with untreated except lower rate of Avaunt ( Table 4 ). Catface injury on fruits treated with Sequoia was lower than untreated but not different from other insecticides except lower rate of Avaunt. None of the treatments elicited any signs of phytotoxicity on strawberry plants after applications.

Author notes