California Red Scale Insecticide trial, 2017

CRS infestations cause downgrading of fruit and in extreme cases yield loss due to twig dieback. A field trial was conducted in a 21-yr-old ‘Powell’ navel orange orchard near Sanger, California, to test the efficacy of various pesticide treatments and water volumes applied to control CRS. CRS densities were determined by counting all live first- and second-instar scales as well as third-instar and mature female scales on five 1-yr-old twigs (23 cm long) and five fruit (when available) randomly selected from around the outside canopy of each tree. There were 10 trees per treatment assigned in an RCB with 10 reps per block based on pretreatment scale densities found on twigs on 2 May 2017. Treatments were applied using a 100-gal high pressure D30 diaphragm pump sprayer with mechanical agitation and a hand wand with a D6 nozzle. The treatments were applied with 0.5% or 1% Omni Spray Oil at 250 psi in 250 or 750 gal of water per acre. The Movento treatments were applied on 6 May, timed for the first generation of crawler emergence. The Centaur treatments were applied on 11 Jul, timed for the second generation crawler of emergence. One set of trees received both Movento in May and Centaur in Jul. Generations were determined by trapping and counting crawlers on double-sided tape wrapped around 1-yr-old wood. CRS densities were evaluated on 26 Jun and 17 Aug on twigs. On 26 Sep, all fruit within reach on the outside of each tree were rated as 0, 1–10, or >10 scaler per fruit to determine the percentage of scale-infested fruit. Data were analyzed using ANOVA and the means were separated according to Fisher’s LSD (P = 0.05) after log₁₀ (x+1) of mean scales per fruit or twig or arcsine (square root (x)) transformation of proportions.

All treatments significantly reduced the mean CRS per twig or fruit compared with the untreated control (Table 1). The treatments with Movento resulted in the lowest densities of CRS.

This research was supported by the California Citrus Research Board and industry gifts of pesticides and funding.