Oil Sprays for California Red Scale Control, 1986

Abstract

Abstract A randomized complete block experiment with 11 single-tree replicates and 3 treatments was conducted in a field of mature lemon trees (ca. 40 yr old) at the University of California, Riverside. Pretreatment densities of California red scale (CRS) were evaluated in mid May by examining in each plot, 75 9-inch twigs (ca. 1 yr old). Each twig was scored in situ as being infested or not infested with live CRS. Plots were assigned to the 11 blocks on the basis of pretreatment CRS density so that within each block initial CRS density was similar among plots. Treatments then were assigned randomly within each block. The 3 treatments were applications of a new formulation and the old formulation of Chevron’s Volck Supreme oil at a concentration of 1.25%, as well as an untreated control. The major differences between the old and new formulations, respectively, are unsulfonated residue (UR rating): 94.3% vs. ≥ 99%; aromatic carbon: 3.9% vs. 0%; naphthenic carbon: 72.5% vs. 31.36%; paraffinic carbon: 23.5% vs. 68.64%; difference between 10% and 90% boiling points at 10 mm Hg: 122° vs 85°F. Applications were made with hand guns from ground level and from a tower at ca. 505 psi at ca. 18 gal/tree, which soaked the trees to the point of runoff. Measurements of the amount of spray in the tank after application of the two oils indicated that either the gallonage per tree or the initial concentration of the oil in the finished spray was 5% greater for the new formulation than for the old formulation. Posttreatment samples were taken in Nov 1986 and again in Jan 1987 by in situ examination of 75 9-inch twigs and 100 fruit in each plot. Twigs were scored as infested or not infested with live CRS. Fruit were scored as having 0, 1-10, or >10 live and/or dead CRS since fruit are downgraded in the packing house when infested with approximately 10 or more live or dead scale.