Evaluation of Materials for Control of Citrus Thrips

The control of citrus thrips is a major concern for citrus growers in the Yuma area. Five materials were evaluated for control of citrus thrips on Lisbon lemons at the Yuma Mesa Agricultural Center during July and August of 1985. Although there was no statistically significant differences between treatments, Mavrik appeared to provide the best control of the materials tested. Dimethoate (Cygon) and formetanate hydrochloride (Carzol) were not tested. INTRODUCTION Citrus thrips are the most serious general pest of citrus in Arizona. Both the developing fruit and leaves of all citrus varieties may be injured and reinfestation on new growth may occur at intervals during the growing season. Feeding on new growth causes distortion, thickening, dwarfing and silvering of the leaves. Attacks on fruit from the time of formation until they reach an inch or more in diameter results in scarring and a lower harvest grade. Treatment of mature trees after the fruit has sized is seldom necessary. Materials commonly used include dimethoate (Cygon) and formetanatc hydrochloride ( Carzol). Although acephate (Orthene) has at times been used in the past, there does not appear to be much hope for its release in the future. There has been much concern about the increase of resistance shown by thrips to the materials in use, which could leave growers without effective control measures. In an effort to find new materials which may be effective in controlling citrus thrips, five compounds were evaluated during July and August of 1985. This was done in cooperation with David Byrne, University of Arizona entomologist, who was evaluating the effectiveness of nine materials for use against citrus flat mites. Unfortunately, since this study was conducted in conjunction with a flat mite study, none of the commonly used thrip materials were included as a standard of comparison. METHODS AND MATERIALS A block of Lisbon lemon trees at the Yuma Mesa Agricultural Center was used for the study. Each treatment was replicated on 3 different trees in a completely randomized design. The citrus thrips population was determined by counting the number of thrips per terminal with new growth. Counts were made on 6 terminals per tree by using a counting box. The test materials were applied July 23, 1985, with a handgun from a John Bean sprayer operating at 300 psi at a rate of 100 gallons per acre. Precounts were taken before application of the test materials and 1, 3, 5, 7, 14, and 21 days afterward. All counts were made between 8:00 and 10:00 A.M. to reduce variation due to migration of the thrips to the interior of the trees. November, 1986 Citrus Report Page 74 RESULTS The only statistically significant differences in treatment means were observed on August 13. Although no treatment was clearly superior, Mavrik appeared to provide the best control of the materials tested as shown in Figure 1. Additional research which includes dimethoate and Carzol as standards of comparison will be necessary to draw any major conclusion. Table L Mean thrips count for each treatment Observation Dates Treatments 7 -23 7 -24 7 -26 7 -30 8 -6 8 -13 8 -20 Danitol 7.1 2.5 1.8 6.5 14.4 14.1 12.5 (2.4 EC) DPX-Y 5893 2.8 4.0 3.3 9.7 13.7 17.0 12.5 (50 WP) Pyrenone 2.4 3.3 5.0 6.2 12.4 18.6 15.8 (CS) Apollo 7.0 11.3 6.8 4.5 14.3 10.3 11.1 (50 SC) Mavrik 5.1 3.1 3.9 3.6 11.3 11.9 12.9 (2 EC) Control 4.3 6.6 4.1 6.6 15.5 14.7 12.9