Miticide efficacy for control of two-spotted spider mite in strawberry, 2024

The efficacy of multiple organic and conventional miticides on two-spotted spider mites (TSSM) was evaluated at the Cal Poly Strawberry Center. The experiment was conducted at Field 25 at Cal Poly (GPS coordinates: N35º18′19.06″; W120º40′33.44″) in San Luis Obispo, CA. Bare root strawberry transplants (Albion) were planted into raised beds on 2 Nov 2023. Beds were covered with 1.1 mm black TIF (totally impermeable film) polyethylene mulch (TriCal Inc., Hollister, CA). The experimental area consisted of 5 beds, 140 ft long. Each strawberry bed was 64 in. center to center, with 4 rows of plants spaced 12 in. between rows and 15.5 in. between plants within a row. Plants were irrigated and fertilized via 3 lines of drip tape per bed. The plot size was a 20 ft long section of a strawberry bed, replicated 4 times and arranged in an RCB. Treatments were applied using a backpack sprayer calibrated to deliver 150 gal/A using compressed CO₂ at 60 psi. The sprayer was equipped with a custom 48-in. handheld boom. The boom had 5 14 in. dropdown tubes and 8 nozzles (ALBUZ ATR 80 red hollow cone, Kisco Sales, Santa Maria, California) in total. The outer 2 dropdown tubes contained a single nozzle angled inward at 45 degrees and the 3 inner tubes contained 2 nozzles, with each nozzle at opposing 45-degree angles. The Broadspred treatment was calibrated to deliver 200 gal/A and contained Mixwell at 24 fl oz/A and Acadian at 64 fl oz/A. Applications were made on 26 Mar and 2 Apr. A presample of 10 mid-tier leaflets was taken the morning prior to the first application. Five mid-tier leaflets were collected per plot 3 days after the first treatment (DAT1), 7 DAT1, 4 days after the second treatment (DAT2), and 7 DAT2. Leaflets were placed in paper bags and transported to the lab. Nymph and adult TSSM were counted under a dissecting microscope within 5 days of sampling. Adult and nymph data were analyzed with ANOVA and Generalized Linear Mixed Model (PROC GLIMMIX) following a normal distribution in SAS (SAS Institute, version 9.4). Means were separated according to Tukey’s HSD.

In the presample, Acramite had significantly fewer nymphs than Kanemite (Table 1), but no significant differences were observed in adults (Table 2). Three days after the first treatment, adults for Kanemite, Acramite, Nealta, and Hop Oil EC statistically separated from the non-treated control. Seican and Saponified Hop Oil were the only treatments that did not separate from the control for nymphs 3 DAT1. Kanemite, Acramite, and Nealta had significantly fewer adults than the control at 7 DAT1, 4 DAT2, and 7 DAT2. Nymphs at 7 DAT1 only separated from the control with Kanemite and Nealta, but at 4 DAT2 Acramite also separated in addition to the latter 2 products. No treatment separated at 7 DAT2 for nymphs, potentially due to outliers in the Hop Oil EC. Phytotoxicity was observed in the Hop Oil EC plots after the first spray, so the rate was dropped to 1.25% v/v for the following spray.