s Sulllnst Monty 632.6 A field 3232 comparison of A3tr81-30.20, 0.35f and 0.50 percent MONTANA DEPARTMENT OF AGRICULTURE haits^fir® ®**“^"-NVIRONMENTAL MANAGEMENT DIVISION TECHNICAL SERVICES BUREAU HELENA, MONTANA 59620 STATT DOCUMENTS COLLECTION DECl 1988 MONTANA STATE LIBRARY 1515 E. 6th AVE. HELENA, MONTANA 59620 A FIELD COMPARISON OF 0.20, 0.35, AND 0.50 PERCENT STRYCHNINE GRAIN BAITS FOR CONTROLLING RICHARDSON GROUND SQUIRRELS by Monty Sul 1 ins Rodent Control Specialist MONTANA STATE LIBRARY S 632.63232 A3tr81-3c.1 Suilins A field comparison of 0.20, 0.3S, and 0. 3 0864 00061489 4 ABSTRACT A field investigation conducted in Wheatland County, Montana, during July 1981, determined that 0.20 percent strychnine grain bait adequately reduced Richard- son ground squirrel activity. Application rates of one tablespoon or one tea- spoon per burrow of 0.20 percent strychnine bait appeared to be equally effec- tive. An accurate comparison among the efficacies of 0.20, 0.35, and 0.50 percent strychnine baits was not possible because of unusual variations and growth of vegetation which adversely affected bait acceptance. Tablespoon quantities of applied bait per burrow left excessive amounts of residual bait under the conditions of this study. One apparent nontarget species fatality, a jackrabbit, was observed on a plot treated with 0.20 percent bait. Technical Report 81-3 July 1981 INTRODUCTION In 1976, strychnine, as a field rodenticide, was placed in the Rebut- table Presumption Against Registration (RPAR) process because of potential hazards to nontarget species, accident history, and acute oral toxicity. As a result, in 1980, the U.S. Environmental Protection Agency released the Strychnine Position Document 2/3 (U.S. Environmental Protection Agency 1980) with recommendations concerning the continued above ground uses of strych- nine. Among EPA's recommendations were standardization of ground squirrel baits at 0.20 percent strychnine and increasing the rate to one level table- spoon of bait per burrow. Montana agricultural interests are concerned that the recommended concentration and rate would not be efficacious, and that alternative rodenticides for ground squirrel control are ineffective. Several Montana agencies requested that EPA delay its final decision until studies could be conducted to investigate effective concentrations and rates of appli- cation. Strychnine grain baits currently registered in Montana have concentrations of 0.35, 0.44, and 0.50 percent active ingredient. The application rate is one teaspoon per burrow for ground squirrels. These baits provide the only effective and economical method for managing Richardson ground squirrels at this time. Alternatives including zinc phosphide, anticoagulants, 1080, and gas cartridges have been ineffective, unproven, not registered, or too expen- sive (Swick 1976, Sullins 1977, Albert and Record 1979, Swick 1980). Until such time as viable alternatives are developed and registered, it is imperative that strychnine bait be available for management of damage caused by Richardson ground squirrels. This study was conducted to help determine the minimum concentrations and rates of active ingredient that will provide consistent economic control of Richardson ground squirrels. A variety of currently used strychnine concen- trations were tested along with EPA's recommended 0.20 percent. OBJECTIVES The objectives of this study were to determine if 0.20 percent strychnine bait would provide efficacious control of Richardson g'round squirrels and to compare observed control with that obtained with 0.35 and 0.50 percent strych- nine grain baits. STUDY AREA Nine study plots were selected on privately owned property approximately 20 miles north of Harlowton, Montana. The plots were located on dryland alfalfa- grass pasture and were similar in vegetation type and physical aspects. Unusu- ally wet spring and early summer conditions (over twice the normal amount of precipitation) resulted in above normal amounts of vegetation on the study area. METHODS AND MATERIALS Using three concentrations of strychnine grain bait, 0.20, 0.35, and 0.50 percent active ingredient on slightly crimped whole oats, field efficacy tests were conducted on eight separate plots (two replications for each test) in- habited by Richardson ground squirrels. A ninth plot received no treatment and was used as a control. Plots varied in size from 0.7 to 3.3 hectares (1.7 to -1- 6.6 acres) and each plot was surrounded by a treated buffer zone (100 yards) to prelude reinvasion. Baits were applied by hand using calibrated clippers, the application rates for the 0.20 percent bait were both one teaspoon and one table- spoon per burrow (on separate plots). For the 0.35 and 0.50 percent baits, the application rate was one teaspoon per burrow as per labeled instructions. These baits were applied in late July after juveniles reached adult size. To quantify the effectiveness of each treatment, visual counts were con- ducted with binoculars pre-and-post treatment to generate activity indices (AI). Visual counts consisted of three counts at five minute intervals on each plot for three consecutive days pre-and-post treatment. Counts were conducted early in the morning during peak periods of foraging activity. Pre-and-post treat- ment activity indices were than computed by averaging the 9 pre-or-post treat- ment visual counts. Precent reduction in activity due to strychnine baiting was computed as follows: Pretreatment AI - Post treatment AI Percent Reduction in Activity = Pretreatment AI X 100 Residual bait counts were conducted one day and seven days post treat- ment to determine amounts of unconsumed bait remaining on the ground. In one plot of each treatment, bait kernals were counted at each of 20 randomly selec- ted burrows. Post baiting searches were conducted to determine nontarget mortalities resulting from strychnine poisoning. RESULTS AND DISCUSSION A comparison of pre-and-post treatment activity indices (Table 1) indicate that the treated strychnine baits reduced Richardson ground squirrel activity within a range of 66 to 86 percent. This reduction was considerably less than the preferred 90 percent or greater. Unusually lush green vegetation was present throughout western and central Montana due to much higher than normal precipitation in the spring and early summer months. The abundance of vege- tation on the study site may have been a major factor in reduced overall bait acceptance. While some livestock grazing had previously occurred on some of the study plots, abundant vegetation was still present. The 0.20 percent treatment with the one teaspoon per burrow rate reduced activity by 85 and 86 percent as compared to 84 and 86 percent for the one tablespoon per burrow rate. These reduction rates were considerably greater than the 0.35 (74 and 66 precent reduction) and 0.50 (79 and 80 percent reduc- tion) percent strychnine baits. However, it should be mentioned that green vegetation was much more abundant on the 0.35 and 0.50 treatment plots, which may have influenced bait acceptance. There was no apparent difference in the reduction of ground squirrel activity between the one teaspoon and one tablespoon rates of 0.20 percent strychnine baits. Although vegetation prevented accurate counts of residual bait left after baiting operations, it was evident that far too much bait remained on the ground four days after bait application with the one table- spoon rate. Considerable amounts of residual bait were also left on the ground on plots treated with one teaspoon rates where hole density was great. This residual bait could be decreased by properly scattering one teaspoon of bait near several closely adjacent holes rather than placing one teaspoon at each hole. Post treatment searches revealed only one apparent nontarget fatality - a whitetail jackrabbit was found on a plot treated with one tablespoon of 0.20 percent strychnine bait. -2- CONCLUSIONS Under the environmental conditions of this study (above normal precipita- tion and vegetative growth), 0.20 percent strychnine grain bait appeared to be effective in reducing Richardson ground squirrel numbers. However, a direct comparison in efficacy between 0.20, 0.35, and 0.50 percent strychnine grain baits was not possible in this study due to variations in and above normal vegetative growth on the various test plots. An application rate of one table- spoon of bait per burrow was considered to have left excessive residual bait on the ground after baiting operations. It is recommended that this study be continued to obtain data under more normal field conditions, perhaps in early spring after the squirrels emerge from hibernation but before green vegetative growth becomes a controlling factor. The bait concentrations used in this study should also be field tes- ted on other pest rodent species to determine comparative efficacy. TABLE 1. ACTIVITY INDICES, PERCENT REDUCTION IN ACTIVITY, AND NONTARGET MORTALITIES ON PLOTS TREATED WITH 0.20, 0.35, AND 0.50 PERCENT STRYCHNINE GRAIN BAITS TO CONTROL RICHARDSON GROUND SQUIRRELS (July 1981). TREATMENT Control 0.20% Strychnine 1 Teaspoon per burrow 0.20% Strychnine 1 Tablespoon per burrow 0.35% Strychnine 1 Teaspoon per burrow 0.50% Strychnine 1 Teaspoon per burrow INDICES Plot A Plot B Plot A Plot B Plot A Plot B Plot A Plot B Pre-Treatment Activity Index 15 26.5 25.0 26.0 35.3 14.3 21.3 23.5 21.2 Post-Treatment , Activity Index 16 4.0 3.5 4.2 4.8 3.7 7.3 5.0 4.3 Q Percent Reduction -- 85.0 86.0 84.0 86.0 74.0 66.0 79.0 80.0 Nontarget Species^ -- -- -- -- 1 white-tailed jack rabbit -- -- -- -- a) b) c) d) Average of 9 counts of active squirrels per plot during 3 days prior to baiting. Average of 9 counts of active squirrels per plot during 3 days after baiting. P re -Treatment AI - Post-Treatment AI Formula: X 100 Pre-Treatment AI Nontarget species carcasses found on or near treated plots within 3 days after baiting. 4 LITERATURE CITED Albert, Steven W. and C. Raymond Record. 1979. Efficacy and cost of four rodenticides for Columbian ground squirrel damage control in Western Montana, Final report, Montana Department of Livestock, Helena. 17 pp Sul 1 ins, Monty. 1977. Evaluation of prebaiting for improving bait accep- tance by Black-tailed prairie dogs. Final report, Montana Department of Livestock, Helena. 6 pp. Sul 1 ins, Monty. 1978. Efficacy and cost of cyclone seeders, motorcycle dispensers, and hand baiting for controlling Black-tailed prairie dogs. Final report, Montana Department of Livestock, Helena. 8 pp. Swick, Craig D. 1976. Afield evaluation of strychnine, zinc phosphide, and 1080 grain baits for prairie dog control. Final report, Montana Depart ment of Livestock, Helena. 8 pp. Swick, Craig D. 1980. A field evaluation of zinc phosphide for reducing Richardson ground squirrels. Final report, Montana Department of Live- stock, Helena. 3 pp. U.S. Environmental Protection Agency. 1980. Strychnine Position Document Number 2/3. Office of Pesticide and Toxic Substances, Washington D.C. 102 pp. -5-