Field Evaluation of An Aqueous Formulation of Carbaryl for Rangeland Grasshopper Control, 1983
Authors: Foster R. Nelson , Onsager Jerome A. , Reuter K. C. , Roland T. 
Published: March 2022

A small plot study (see J. A. Onsager and P. C. Mazuranich, 1983, Insecticide and Acaricide Tests 8:204) indicated the potential of reduced rates of carbaryl in an aqueous formulation for control of rangeland grasshoppers. The objective of this study was to determine if lower rates of carbaryl would be effective when used in an aqueous formulation on larger plots. The Sevin FR formulation of carbaryl was applied at dosages of 0.250 and 0.375 lb (AI)/acre (8 and 12 fluid oz) to 320 acres (0.5 X 1 mile) plots near Big Timber, Montana, on 23 Jul and 24 Jul ‘83. Both treatments were applied in 20 fluid oz of mix/acre, each containing 4 oz of water plus either 8 oz or 4 oz respectively, of PA3 (an antidrift additive containing molasses). These treatments were compared to standard rangeland treatments of 0.5 lb (AI) carbaryl/acre (16 fluid oz of Sevin-4-Oil diluted with 4 oz of diesel/acre) and 0.58 lb (AI) malathion/acre (8 fluid oz of Cythion) applied to adjacent 320-acre plots (0.5 x 1 mile and 0.25 x 2 miles, respectively) on 24 and 26 Jul, respectively. All treatments were applied from a Cessna Ag Truck aircraft operating at 120 mph. All treatments were applied through flat fan stainless steel jet nozzle tips from an altitude of 50 to 75 ft with a swath of 100 ft. Seven 8006 tips directed 45° down and aft were used for the 0.250 and 0.375 lb (AI)/acre Sevin FR treatments (43 psi and 41 psi, respectively). Ten 8004 tips directed straight down and operating at 35 psi were used for delivering the Sevin-4-oil treatment and eleven 80015 tips directed straight down at 40 psi were used for applying the Cythion. Pre and postapplication grasshopper densities were ascertained by counting grasshoppers in forty 0.1 m2 rings, 5 m apart, arranged for the duration of the study in circles or diagonal transects at 8 sites within each block (1 transect contained only 29 rings). Pre-treatment counts were taken 1 to 2 days prior to treatment and posttreatment counts were conducted 5 times during a period of 21 days following treatment. Grasshopper densities from 59 counts between 20 Jul to 16 Aug ‘83, at 9 untreated sites adjacent to the treatment area were used to determine the natural change in the grasshopper population during the study. Data expressed as a percentage survival based on pretreatment counts in the same plot were adjusted for the natural population change by Abbott’s formula. Sums of the ranks of the percentage control at 19 to 21 days postapplication for each of the treatments were compared by a nonparametric multiple comparison procedure. (See J. H. Zar, 1974, Biostatistical Analysis, pp 156–157.) Mean daily percentage control values from 2 to 19 days after application for each of the treatments were also ranked and the treatment sums compared as above. The above species were mostly fourth (36%) and fifth (38%) instars and respectively comprised 43.1, 21.2, 14.1, 4.1, and 4.0 of the grasshopper population in the treatment plots before application. Pretreatment densities ranged from 2.3 to 25.3 and averaged 11.4 grasshoppers/m2 in the treated plots.