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The effectiveness of five rodenticides and three application procedures in controlling Microtine voles (Microtus montanus) in Washington State apple orchards
C R O P P R O T E C T I O N (1987) 6 (4), 277-279
The effectiveness of five rodenticides and three application procedures in controlling Microtine voles (Microtus montanus) in Washington State apple orchards RAYMOND E . H U N T E R * , LEONARD R . ASKHAM AND MICHAEL E. R . GODFREY**
Cooperative Extension, Washington State University, Pullman, Washington 9M64-6412, USA ABSTRACT. Four formulations of the acute toxicant zinc phosphide and one formulation of the subacute toxicant chlorophacinone were evaluated on voles (Microtus montanus) in two Red and Golden Delicious apple orchards in north central Washington during the spring. Three treatment techniques combining cultural practices with differing methods of bait application were compared concurrently. Raking, followed by a single broadcast application of baits or the hand-placement of baits, was the most effective treatment. A second bait application gave a slight improvement only when no cultural work was done, and then only with two of the five baits tested. Whole wheat and steam-rolled oat baits with 2% zinc phosphide and Rozol® chlorophacinone baits were usually more effective than zinc phosphide on cracked corn or ZP Rodent Bait AG ® .
Introduction
A great deal of emphasis has been placed on controlling pine voles (Microtus pennsylvanicus pinetorum) in eastern United States apple orchards to reduce damage caused by their feeding on the cambium roots. Byers (1984, 1985) and others (Horsfall, 1956; Byers, Young and Neely, 1976; Byers, Merson and Palmateer, 1982; Siddiqui, Blaine and Taylor, 1983; Merson and Byers, 1985) have conducted extensive field efficacy trials on a number of rodenticides. Some have provided good results while others have not. Field efficacy trials with the Microtine Vole (Microtus montanus), common in the western United States, have been more limited. Studies by Marsh and others (Marsh, 1977 and undated; Marsh and Howard, 1975; Salmon and Marsh, 1979; Marsh and Tunberg, 1984; Marsh, Howard and Jackson, 1980; Salmon et al., 1984) have explored the use of various toxicants on carriers. None of their work has assessed these materials under different application procedures in apple orchards. The ways in which apple orchards are maintained-including the ground vegetation under the tree canopy --to limit vole activity have been explored by a few researchers (Byers, 1976; Byers and Young, 1974, 1978). * Now retired. * * Present address: J. T. Eaton & Co. Inc., Twinsburg, Ohio, USA. 0261-2194/87/04/0277-03 $03.00 © 1987 Butterworth & Co (Publishers) Ltd
In general, it has been found that clean agricultural practices, i.e. frequent mowings and use of herbicides, reduce vole predation problems. Although providing substantial population suppression during periods of low population density, cultural work alone may not give adequate control (to prevent more damage) during times of peak population density, particularly in winters with heavy snow pack accumulation. The purpose of these trials was to test the efficacy of four commonly used zinc phosphide and one chlorophacinone-treated rodenticide bait, and the effect of pre-application cultural treatments, on Microtine voles in a production apple orchard. Materials and m e t h o d s
Three sites were located in two Golden and Red Delicious apple orchards near Quincy, Washington, USA. Plots 1 and 2 were established in a 10-year-old orchard with 2 " 7 x S ' 4 m spacing of trees. This orchard had a dense understory of creeping red rescue (Festuca spp.). Plot 3 was established in a young (14-leaf stage) orchard with 3 x 3 m spacing. The understory vegetation in this orchard was native species of water and foxtail grasses (Hordeum spp.). Following the procedure developed by Byers (1975) and modified by Godfrey (1986), 50 apple slices were placed in active runways or near burrow openings scattered throughout each plot prior to treatment. The
Rodenticides and their application in apple orchards
278
apple slices were inspected for tooth marks at 24h intervals for 3 days. The results were tabulated and the means calculated. Fresh apple slices were used each day. Seven days after each rodenticide application, the same number of fresh apple slices were again placed at each previously identified location and observed for feeding signs as in the pretreatment assessment. Each bait (Table 1) was applied twice at 11.2kg/ha (101b/acre) to the three test sites. At Site 1 the baits were broadcast with a Casaron hand-spreader over the undisturbed vegetation under the apple trees; at Site 2 the vegetation had been hand-raked to expose the vole runways and burrow openings immediately prior to broadcasting the baits, and at Site 3 the rodenticides were hand-placed directly in each burrow opening following hand-raking. Replicating test plot conditions, control plots were also established at each site. The second bait application was made 3 weeks after the first application. No precipitation fell during the trial period but heavy dews and frosts were reported. Results
Significant differences were found between the baits, methods of bait application and cultural practices (Table 1). The greatest population reduction occurred when any of the rodenticides were either hand-placed into the burrow openings and runways or broadcast directly following raking. The differences between these two and the broadcast application over undisturbed vegetation were striking. No rodenticide, either from a single or double application, provided effective control (>85% mortality) when the bait did not penetrate the grass
cover to reach the runways and burrow openings (Table 1). When raking preceded broadcast applications, allowing the baits to reach the ground, all of the bait formulations provided effective control. There was no apparent additional benefit from a second application after the runways had been opened or where baits were hand placed directly into the runway systems following raking.
Discussion
These data show that even minimal cultural work preceding application of rodenticides, plus the careful application of these compounds, can significantly reduce the target population. The amount of toxic bait needed to achieve control is also reduced by avoiding the need for repetition of treatments. Baits broadcast over undisturbed vegetation seldom penetrate to the rodent's feeding area next to the soil and are therefore unavailable to the animal. Consequently, no rodenticide would be effective without some degree of preliminary cultural work. If an arbitrary maximum of five out of 50 apple slices nibbled is designated an index of successful control (i.e. an activity index of 10% or less indicating 90% or more of the area free of voles) it is apparent that any control strategy not preceded by cultural work is ineffective. When raking preceded the application of toxicant, steam-rolled oats or whole wheat treated with zinc phosphide, or chlorophacinone pellets, were effective with a single application. Only where runways were grass-covered did a second application significantly improve the level of control achieved.
TABLE 1. Effectiveness of two rodenticides on five baits under three application procedures in two orchards in north central Washington State (USA), M a r c h 1985
Treatment type*
Apple slices fed o n t b e f o r e first treatment
Slices fed o n t after first treatment
Mortality (%)
Corrected mortality
Slices fed o n t after second treatment
2°70 zinc phosphide on cracked corn
1 2 3
41 44 34
27 9 11
34 80 68
36 82 70
20 6 8
51 86 76
46 84 71
2°70 zinc phosphide on whole wheat
1 2 3
46 46 39
22 4 3
52 91 92
55 94 95
14 2 1
70 96 97
65 93 92
2% zinc phosphide on steam-rolled oats
1 2 3
42 41 44
29 3 2
31 93 95
33 95 98
18 2 0
57 95 100
52 93 95
2°70 zinc phosphide pellets on whole wheat (ZP Rodent Bait A G e )
1 2 3
38 38 41
27 7 5
29 82 88
31 84 90
19 5 3
50 87 93
45 84 88
Chlorophacinone paraffmized pellets (Rozol ® )
1 2 3
44 45 44
21 2 1
52 96 98
55 98 100
11 0 0
75 100 100
70 97 100
Control
1 2 3
43 40 40
44 41 41
+ 2.3 +2-5 +2.5
0 0 0
41 39 38
T o x i n baits
Mortality (%)
5.0 2.5 5.0
Corrected mortality
0 0 0
* Treatment types: (1) bait broadcast over grass-covered runways and holes; (2) bait broadcast after grass cover was raked away from runways and holes; (3) bait hand placed in grasscovered runways and holes. t Average of three-day feeding period on 50 slices/day.
CROP PROTECTION Vol. 6 August 1987
R. E. HUNTER, L. R. ASKHAMAND M. E. R. GODFREY
Acknowledgements Special thanks are e x t e n d e d to R & M E x t e r m i n a t o r s , C h e n e y , W a s h i n g t o n , O r e g o n R o d e n t C o n t r o l Outfitters and C h e m p a r C o r p o r a t i o n for p r o v i d i n g the rodenticide baits used d u r i n g these trials; to D a v e B u r n e t t a n d F o r n e y F r u i t and P r o d u c e for the use o f their orchards; a n d to J e r r y T a n g r e n for statistical advice.
References BYERS,R. E. (1975). A rapid method for assessing pine vole control
in orchards. Journal of the American Society for Horticultural Science 10, 391-392. BYERS, R. E. (1976). Review of Pine Vole Control Methods. In: Virginia Fruit Proceedings, 8th Annual Meeting of Virginia State Horticultural Society 64 (3), 1. BYERS, R. E. (1984). Control and management of vertebrate pests in deciduous orchards of the Eastern United States. In: Horticultural Reviews, Vol. 6, pp. 253-285 (ed. by J. Janick). Westport, CT: AVI. BYERS, R. E. (1985). Ground cover sprays versus baiting for the control of Microtine rodents. Actda zoologica fennica 173, 173-174. BYERS, R. E. AND YOUNG, R. S. (1974). Cultural management of pine voles in apple orchards. Journal of the American Society for Horticultural Science 9, 445-446. BYERS, R. E. AND YOUNG, R. S. (1978). Effect of orchard culture on pine vole activity. Journal of the American Society for Horticultural Science 103, 625-626. BYERS, R. E., YOUNG, R. S. AND NEELY, R. D. (1976). Review of cultural and other control methods for reducing pine vole populations in apple orchards. In: Proceedings, Seventh Vertebrate Pest Control Conference, Monterey, California, 9-11 March, pp. 242-253 (ed. by T. P. Salmon). University of California, Davis: Vertebrate Pest Council. BYERS, R. E., MERSON, M. H. AND PALMATEER,S. D. (1982). Control of orchard voles with broadcast baits. Journal of the American Society for Horticultural Science 107, 613-619. GODFREY, M. E. R. (1986). Assessment of a vole population. Journal of Wildlife Management, in press.
279
HORSFALL,R., JR (1956). Pine mouse control with ground-sprayed endrin. Proceedings of the American Society .for Horticultural Science 67, 68-74. MARSH, R. E. (undated). Safety Measures Taken to Minimize Potential Primary Hazard to Nontarget Species when Baiting Field Rodents. (Mimeo.)Davis: University of California. MARSH, R. E. (1977). Sciurid diets. In: Handbook Series in Nutrition and Food. Section G: Diets, Culture Media, Food Supplements, vol. 1, pp. 65-78 (ed. by M. Rechcigl, Jr). Cleveland: CRC Press. MARSH, R. E. AND HOWARD,W. E. (1975). A New Series of Acute Rodenticides. World Health Organization Manuscript WHO/ VBC/75.563. Geneva: WHO. 9 pp. MARSH, R. E., HOWARD, W. E. AND JACKSON, W. B. (1980). Bromadiolone: a new toxicant for rodent control. Pest Control 48, 22, 24, 26. MARSH, R. E. AND TUNBERG, A. D. (1984). Research on Meadow Mouse (Microtus californicus) Biology and its Control Relative to Artichoke Production. Progress Report. Davis: Wildlife & Fisheries Biology, University of California. (Available on request.) MERSON, M. H. AND BYERS, R. E. (1985). Weathering and the field efficacy of pelletized rodenticide baits in orchards. Crop Protection 4, 511-519. SALMON, T. P. AND MARSH, R. E. (1979). Age as a Factor in Rodent Susceptibility to Rodenticides--A Review. American Society for Testing and Materials. Special Technical Publication 680. Philadelphia, PA: ASTM. SALMON, T., GORENZEL, W. P., MARSH, R. AND HUTTON, G. (1984). Rodent control down on the farm. Pest Control Technology (Reprint supplied by Chempar Products, Division of Lipha Chemicals, Inc.) SIDDIQUI, Z., BLAINE, D. AND TAYLOR,S. (1983). Meadow Vole Control in Ontario Apple Orchards. Toronto, Canada: Chemical Research International (unpublished report).
Received 13 December 1985 Revised 13 August 1986 Accepted 15 December 1986
CROP PROTECTION Vol. 6 August 1987
The effectiveness of five rodenticides and three application procedures in controlling Microtine voles (Microtus montanus) in Washington State apple orchards RAYMOND E . H U N T E R * , LEONARD R . ASKHAM AND MICHAEL E. R . GODFREY**
Cooperative Extension, Washington State University, Pullman, Washington 9M64-6412, USA ABSTRACT. Four formulations of the acute toxicant zinc phosphide and one formulation of the subacute toxicant chlorophacinone were evaluated on voles (Microtus montanus) in two Red and Golden Delicious apple orchards in north central Washington during the spring. Three treatment techniques combining cultural practices with differing methods of bait application were compared concurrently. Raking, followed by a single broadcast application of baits or the hand-placement of baits, was the most effective treatment. A second bait application gave a slight improvement only when no cultural work was done, and then only with two of the five baits tested. Whole wheat and steam-rolled oat baits with 2% zinc phosphide and Rozol® chlorophacinone baits were usually more effective than zinc phosphide on cracked corn or ZP Rodent Bait AG ® .
Introduction
A great deal of emphasis has been placed on controlling pine voles (Microtus pennsylvanicus pinetorum) in eastern United States apple orchards to reduce damage caused by their feeding on the cambium roots. Byers (1984, 1985) and others (Horsfall, 1956; Byers, Young and Neely, 1976; Byers, Merson and Palmateer, 1982; Siddiqui, Blaine and Taylor, 1983; Merson and Byers, 1985) have conducted extensive field efficacy trials on a number of rodenticides. Some have provided good results while others have not. Field efficacy trials with the Microtine Vole (Microtus montanus), common in the western United States, have been more limited. Studies by Marsh and others (Marsh, 1977 and undated; Marsh and Howard, 1975; Salmon and Marsh, 1979; Marsh and Tunberg, 1984; Marsh, Howard and Jackson, 1980; Salmon et al., 1984) have explored the use of various toxicants on carriers. None of their work has assessed these materials under different application procedures in apple orchards. The ways in which apple orchards are maintained-including the ground vegetation under the tree canopy --to limit vole activity have been explored by a few researchers (Byers, 1976; Byers and Young, 1974, 1978). * Now retired. * * Present address: J. T. Eaton & Co. Inc., Twinsburg, Ohio, USA. 0261-2194/87/04/0277-03 $03.00 © 1987 Butterworth & Co (Publishers) Ltd
In general, it has been found that clean agricultural practices, i.e. frequent mowings and use of herbicides, reduce vole predation problems. Although providing substantial population suppression during periods of low population density, cultural work alone may not give adequate control (to prevent more damage) during times of peak population density, particularly in winters with heavy snow pack accumulation. The purpose of these trials was to test the efficacy of four commonly used zinc phosphide and one chlorophacinone-treated rodenticide bait, and the effect of pre-application cultural treatments, on Microtine voles in a production apple orchard. Materials and m e t h o d s
Three sites were located in two Golden and Red Delicious apple orchards near Quincy, Washington, USA. Plots 1 and 2 were established in a 10-year-old orchard with 2 " 7 x S ' 4 m spacing of trees. This orchard had a dense understory of creeping red rescue (Festuca spp.). Plot 3 was established in a young (14-leaf stage) orchard with 3 x 3 m spacing. The understory vegetation in this orchard was native species of water and foxtail grasses (Hordeum spp.). Following the procedure developed by Byers (1975) and modified by Godfrey (1986), 50 apple slices were placed in active runways or near burrow openings scattered throughout each plot prior to treatment. The
Rodenticides and their application in apple orchards
278
apple slices were inspected for tooth marks at 24h intervals for 3 days. The results were tabulated and the means calculated. Fresh apple slices were used each day. Seven days after each rodenticide application, the same number of fresh apple slices were again placed at each previously identified location and observed for feeding signs as in the pretreatment assessment. Each bait (Table 1) was applied twice at 11.2kg/ha (101b/acre) to the three test sites. At Site 1 the baits were broadcast with a Casaron hand-spreader over the undisturbed vegetation under the apple trees; at Site 2 the vegetation had been hand-raked to expose the vole runways and burrow openings immediately prior to broadcasting the baits, and at Site 3 the rodenticides were hand-placed directly in each burrow opening following hand-raking. Replicating test plot conditions, control plots were also established at each site. The second bait application was made 3 weeks after the first application. No precipitation fell during the trial period but heavy dews and frosts were reported. Results
Significant differences were found between the baits, methods of bait application and cultural practices (Table 1). The greatest population reduction occurred when any of the rodenticides were either hand-placed into the burrow openings and runways or broadcast directly following raking. The differences between these two and the broadcast application over undisturbed vegetation were striking. No rodenticide, either from a single or double application, provided effective control (>85% mortality) when the bait did not penetrate the grass
cover to reach the runways and burrow openings (Table 1). When raking preceded broadcast applications, allowing the baits to reach the ground, all of the bait formulations provided effective control. There was no apparent additional benefit from a second application after the runways had been opened or where baits were hand placed directly into the runway systems following raking.
Discussion
These data show that even minimal cultural work preceding application of rodenticides, plus the careful application of these compounds, can significantly reduce the target population. The amount of toxic bait needed to achieve control is also reduced by avoiding the need for repetition of treatments. Baits broadcast over undisturbed vegetation seldom penetrate to the rodent's feeding area next to the soil and are therefore unavailable to the animal. Consequently, no rodenticide would be effective without some degree of preliminary cultural work. If an arbitrary maximum of five out of 50 apple slices nibbled is designated an index of successful control (i.e. an activity index of 10% or less indicating 90% or more of the area free of voles) it is apparent that any control strategy not preceded by cultural work is ineffective. When raking preceded the application of toxicant, steam-rolled oats or whole wheat treated with zinc phosphide, or chlorophacinone pellets, were effective with a single application. Only where runways were grass-covered did a second application significantly improve the level of control achieved.
TABLE 1. Effectiveness of two rodenticides on five baits under three application procedures in two orchards in north central Washington State (USA), M a r c h 1985
Treatment type*
Apple slices fed o n t b e f o r e first treatment
Slices fed o n t after first treatment
Mortality (%)
Corrected mortality
Slices fed o n t after second treatment
2°70 zinc phosphide on cracked corn
1 2 3
41 44 34
27 9 11
34 80 68
36 82 70
20 6 8
51 86 76
46 84 71
2°70 zinc phosphide on whole wheat
1 2 3
46 46 39
22 4 3
52 91 92
55 94 95
14 2 1
70 96 97
65 93 92
2% zinc phosphide on steam-rolled oats
1 2 3
42 41 44
29 3 2
31 93 95
33 95 98
18 2 0
57 95 100
52 93 95
2°70 zinc phosphide pellets on whole wheat (ZP Rodent Bait A G e )
1 2 3
38 38 41
27 7 5
29 82 88
31 84 90
19 5 3
50 87 93
45 84 88
Chlorophacinone paraffmized pellets (Rozol ® )
1 2 3
44 45 44
21 2 1
52 96 98
55 98 100
11 0 0
75 100 100
70 97 100
Control
1 2 3
43 40 40
44 41 41
+ 2.3 +2-5 +2.5
0 0 0
41 39 38
T o x i n baits
Mortality (%)
5.0 2.5 5.0
Corrected mortality
0 0 0
* Treatment types: (1) bait broadcast over grass-covered runways and holes; (2) bait broadcast after grass cover was raked away from runways and holes; (3) bait hand placed in grasscovered runways and holes. t Average of three-day feeding period on 50 slices/day.
CROP PROTECTION Vol. 6 August 1987
R. E. HUNTER, L. R. ASKHAMAND M. E. R. GODFREY
Acknowledgements Special thanks are e x t e n d e d to R & M E x t e r m i n a t o r s , C h e n e y , W a s h i n g t o n , O r e g o n R o d e n t C o n t r o l Outfitters and C h e m p a r C o r p o r a t i o n for p r o v i d i n g the rodenticide baits used d u r i n g these trials; to D a v e B u r n e t t a n d F o r n e y F r u i t and P r o d u c e for the use o f their orchards; a n d to J e r r y T a n g r e n for statistical advice.
References BYERS,R. E. (1975). A rapid method for assessing pine vole control
in orchards. Journal of the American Society for Horticultural Science 10, 391-392. BYERS, R. E. (1976). Review of Pine Vole Control Methods. In: Virginia Fruit Proceedings, 8th Annual Meeting of Virginia State Horticultural Society 64 (3), 1. BYERS, R. E. (1984). Control and management of vertebrate pests in deciduous orchards of the Eastern United States. In: Horticultural Reviews, Vol. 6, pp. 253-285 (ed. by J. Janick). Westport, CT: AVI. BYERS, R. E. (1985). Ground cover sprays versus baiting for the control of Microtine rodents. Actda zoologica fennica 173, 173-174. BYERS, R. E. AND YOUNG, R. S. (1974). Cultural management of pine voles in apple orchards. Journal of the American Society for Horticultural Science 9, 445-446. BYERS, R. E. AND YOUNG, R. S. (1978). Effect of orchard culture on pine vole activity. Journal of the American Society for Horticultural Science 103, 625-626. BYERS, R. E., YOUNG, R. S. AND NEELY, R. D. (1976). Review of cultural and other control methods for reducing pine vole populations in apple orchards. In: Proceedings, Seventh Vertebrate Pest Control Conference, Monterey, California, 9-11 March, pp. 242-253 (ed. by T. P. Salmon). University of California, Davis: Vertebrate Pest Council. BYERS, R. E., MERSON, M. H. AND PALMATEER,S. D. (1982). Control of orchard voles with broadcast baits. Journal of the American Society for Horticultural Science 107, 613-619. GODFREY, M. E. R. (1986). Assessment of a vole population. Journal of Wildlife Management, in press.
279
HORSFALL,R., JR (1956). Pine mouse control with ground-sprayed endrin. Proceedings of the American Society .for Horticultural Science 67, 68-74. MARSH, R. E. (undated). Safety Measures Taken to Minimize Potential Primary Hazard to Nontarget Species when Baiting Field Rodents. (Mimeo.)Davis: University of California. MARSH, R. E. (1977). Sciurid diets. In: Handbook Series in Nutrition and Food. Section G: Diets, Culture Media, Food Supplements, vol. 1, pp. 65-78 (ed. by M. Rechcigl, Jr). Cleveland: CRC Press. MARSH, R. E. AND HOWARD,W. E. (1975). A New Series of Acute Rodenticides. World Health Organization Manuscript WHO/ VBC/75.563. Geneva: WHO. 9 pp. MARSH, R. E., HOWARD, W. E. AND JACKSON, W. B. (1980). Bromadiolone: a new toxicant for rodent control. Pest Control 48, 22, 24, 26. MARSH, R. E. AND TUNBERG, A. D. (1984). Research on Meadow Mouse (Microtus californicus) Biology and its Control Relative to Artichoke Production. Progress Report. Davis: Wildlife & Fisheries Biology, University of California. (Available on request.) MERSON, M. H. AND BYERS, R. E. (1985). Weathering and the field efficacy of pelletized rodenticide baits in orchards. Crop Protection 4, 511-519. SALMON, T. P. AND MARSH, R. E. (1979). Age as a Factor in Rodent Susceptibility to Rodenticides--A Review. American Society for Testing and Materials. Special Technical Publication 680. Philadelphia, PA: ASTM. SALMON, T., GORENZEL, W. P., MARSH, R. AND HUTTON, G. (1984). Rodent control down on the farm. Pest Control Technology (Reprint supplied by Chempar Products, Division of Lipha Chemicals, Inc.) SIDDIQUI, Z., BLAINE, D. AND TAYLOR,S. (1983). Meadow Vole Control in Ontario Apple Orchards. Toronto, Canada: Chemical Research International (unpublished report).
Received 13 December 1985 Revised 13 August 1986 Accepted 15 December 1986
CROP PROTECTION Vol. 6 August 1987