The North Dakota Grasshopper Integrated Pest Management Demonstration Project
By Mark A. Quinn, R. Nelson Foster, Wendal J. Cushing, David C. Hirsch, Keith Winks, and K. Christian Reuter¹
 

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United States Department of Agriculture
Animal and Plant Health Inspection Service
Technical Bulletin No. 1891, Issued December 2000
 

Abstract

The North Dakota Grasshopper Integrated Pest Management (GHIPM) Demonstration Project was established from 1987 to 1993 in western North Dakota and eastern Montana. The objectives of the project were: (1) to manage grasshopper populations in the study area, (2) to compare the effectiveness of an integrated pest management (IPM) program for rangeland grasshoppers with the effectiveness of a standard chemical control program on a regional scale, (3) to determine the effectiveness of early sampling in detecting incipient grasshopper infestations, (4) to quantify short- and long-term responses of grasshopper populations to treatments, and (5) to develop and evaluate new grasshopper suppression techniques that have minimum effects on non-target species.

Three adjacent blocks of rangeland were used for the project. The 3,431-km² (847,815-acre) demonstration block was managed with available IPM techniques, such as conducting intensive grasshopper surveys to define more accurately areas of infestation, using Nosema locustae baits and insecticidal baits, treating small areas of infestation (hot spots) to prevent larger outbreaks, increasing the swath width of aerial applications of insecticidal baits, and by optimally timing treatments. An adjacent 5,294-km² (1,308,171-acre) standard block was managed with conventional chemical control techniques. In this block, large areas exceeding 4,047 ha or 10,000 acres were treated with carbaryl sprays. A 4,373-km² (1,080,588-acre) untreated control block was established in an adjacent section in eastern Montana.

The effectiveness of IPM in managing grasshopper populations on a regional scale was evaluated by comparing grasshopper populations and control method data in the two treatment blocks in North Dakota (i.e., the demonstration block and the standard block). Specifically, the following variables were examined: (1) number of sampling sites in the adult and nymphal surveys, (2) area treated, (3) cost of treatment, (4) amount of insecticide applied, (5) densities of grasshoppers, and (6) frequency distribution of grasshoppers.

The effectiveness of treatments in the demonstration block was evaluated by conducting grasshopper population surveys before and after treatments. Treatments included (1) aerial application of 2.5 x 10⁹ spores of Nosema locustae on wheat bran per hectare (1 x 10⁹ spores/acre); (2) aerial application of 2-percent carbaryl-bran bait applied at a rate of 1.68 kg/ha (1.5 lb/acre); (3) aerial application of malathion sprays applied as 585 mL of Malathion-ULV^® per hectare (8 fluid oz/acre); (4) aerial application of carbaryl sprays at 1.46 L/ha (20 oz/acre) of a 4:1 Sevin-4-oil^® and diesel mix per hectare (8 oz active ingredient [AI] per acre); (5) ground application of 2-percent carbaryl-bran bait applied at a rate of 2.24 kg/ha (2.0 lb/acre); and (6) aerial application of 2-percent carbaryl-bran bait at 1.68 kg/ha (1.5 lb/acre) over an extended swath width.

Approximately twice as many sections (i.e., 640-acre blocks) of rangeland were sampled in the demonstration block as in the standard block. From 1987 to 1993, 62,214 ha (153,734 acres) were treated in the demonstration block, while 121,110 ha (299,268 acres) were treated in the standard block. Most treated areas in the demonstration block were smaller than 1,000 ha (2,471 acres); most treated areas in the standard block were larger than 13,000 ha (32,124 acres). The total amount of insecticide active ingredient (i.e., of carbaryl and malathion) applied to rangeland from 1987 through 1993 was at least 2.5 times greater in the standard block than in the demonstration block. Total treatment costs were 65 percent greater in the standard block than in the demonstration block.

Grasshopper populations were generally similar in the demonstration and standard blocks. Grasshopper densities were significantly greater in the standard block than in the demonstration block in 1987 and 1992 but not in 1988 through 1991 or in 1993. The standard block seemed to support larger grasshopper infestations than the demonstration block, particularly in 1987, 1990, and 1992.

Sixty-five species of grasshoppers were collected from 393 evaluation sites within the demonstration block on the pretreatment sampling dates from 1987 through 1993. Melanoplus sanguinipes and M. infantilis were the two most abundant species, constituting, respectively, 16.4 and 15.4 percent of all grasshoppers collected. Forty-six species were relatively rare, constituting less than 1 percent of the total collected.

A 3-year study of the effect of Nosema-bran bait on grasshoppers suggested that the microbial insecticide had little, if any, effect on grasshoppers either immediately after treatment or in subsequent years.

Aerial and ground applications of malathion and carbaryl sprays were the most efficacious treatments. Immediate reductions in the total number of grasshoppers at the nine blocks treated with these insecticides ranged from 84 to 99 percent.

The effects of carbaryl-bran bait on grasshoppers were assessed at 22 evaluation sites in 3 aerial-application and 6 ground-application experiments. Total populations of grasshoppers were reduced by an average of 44.5 percent at the evaluation sites in the treated areas but declined by an average of only 3.3 percent at 18 untreated control sites. Ground and aerial applications had similar short-term effects on populations of total grasshoppers. The moderate levels of control from carbaryl-bran baits were caused, in part, by the species composition of grasshoppers. The percent reduction in total grasshoppers was negatively correlated (r = -0.41) with the percentage of bran-rejecting species in the treated areas.

The treatment of small areas of infestation, or hot spots, with ground applications of malathion sprays or carbaryl-bran baits was effective in suppressing grasshopper populations. Two applications of carbaryl-bran bait were needed to control grasshoppers in some cases, particularly when initial densities were very high.

Eighteen field experiments compared grasshopper populations in treated sites and untreated control sites (excluding the Nosema-bran bait experiment) a year after treatment. Overall, populations at treatment evaluation sites declined by an average of 53.2 percent a year after treatment. In contrast, densities at untreated control sites increased by an average of 33.6 percent a year after treatment. The data suggest that, in general, treatments were effective in suppressing second-year populations of grasshoppers.

We conclude that increased sampling to delineate more exactly the area of grasshopper infestation, carefully timed treatment applications, and the use of hot-spot treatments with ground applications of either insecticidal sprays or baits should be incorporated into grasshopper IPM programs as alternatives to large-scale aerial applications of insecticidal sprays. Results from the North Dakota GHIPM Demonstration Project indicate that adopting these more intensive management methods will greatly reduce both the cost of grasshopper control treatments and the amount of insecticide applied to rangeland.
 

Author Information

¹ Mark Quinn is an Assistant Scientist in the Department of Crop and Soil Sciences, Washington State University, Pullman, WA. Nelson Foster and Chris Reuter are entomologists with the U.S. Department of Agriculture, Animal and Plant Health Inspection Service's Plant Protection and Quarantine (PPQ) unit in Phoenix, AZ. Keith Winks is the State Plant Health Director for PPQ in Bismarck, ND.