Citrus Thrips Control and Impact on California Red Scale, 1988

Abstract

Abstract Insecticides for the control of citrus thrips populations were evaluated during spring, 1988 in Field 93 (5-yr old Washington Navel oranges) located at the University of California Lindcove Field Station near Exeter, Calif. The effect of these pesticides on California red scale was also evaluated. Pesticides were applied one d after petal fall (on 26 Apr) with a Bean hand sprayer set at 500 psi, outside coverage, and 200 gal/acre. Seventy-seven single tree plots were assigned to 11 blocks (7 trees per block) based on California red scale pretreatment levels so that the 7 trees within each block had similar pretreatment infestations of California red scale. One tree in each block then was assigned randomly to each treatment. Thus, the experimental design for California red scale data was a randomized complete block which was analyzed by 2-way ANOVA. However, the criterion for blocking was irrelevant to thrips populations, therefore the thrips data was analyzed by 1-way ANOVA and included 4 additional untreated control trees that were not included in the randomized complete block design for red scale. California red scale levels on twigs were monitored prior to treatment (in early Apr, 1988) and two mo after treatment by recording the number of twigs (9 inches long, twigs approximately 1-yr-old) infested with live adult female California red scale (n = 75 twigs per plot). Citrus thrips fruit scarring counts were taken prior to harvest (25 Nov) on all fruit on the exterior of the tree from knee to eye level. Scarring was rated as: (a) none, (b) slight (any citrus thrips scarring), or (c) severe (complete ring scar or extensive surface scarring at a level that would cause downgrading of fruit in a commercial operation). Economic scarring levels in a normal yr are approximately 5% severe scars.