Efficacy
This method normally will result in 80 to 95 percent control, which is approximately 5 to 15 percent lower mortality than with a standard (high rate, blanket coverage) treatment. Leaving low densities of grasshoppers after RAATs does not necessarily result in a subsequent outbreak (see Environment below).
Economics
Using RAATs will reduce costs by approximately 50 to 60 percent, depending on the agent and swath width. For example, if a standard application costs $2.50 per acre, the equivalent RAAT program should cost approximately $1.15 per acre protected. In some cases, costs are reduced by two-thirds. It should be noted that the greatest economic benefits derive from increased swath spacing since this effectively decreases the costs for both purchasing insecticides and application.
Environment
RAATs mean 60 to 75 percent less insecticide is applied to our rangelands for grasshopper control. The untreated swaths harbor species essential to rangeland ecosystems, including biocontrol agents of grasshoppers and weeds. Low densities of surviving grasshoppers allow predators and parasites in the untreated refuges to recolonize and thereby reestablish natural regulation of grasshopper populations. For these reasons, RAAT programs also may sustain higher densities of birds than blanket applications.
Research conducted by University of Wyoming and USDA scientists, in cooperation with state departments of agriculture and weed and pest districts, has involved 260 40-acre experimental plots and 19 640-acre operational trials at densities of 7 to 70 grasshoppers per square yard, from 1995 to 2002. Successful operational RAAT programs have been conducted in eight western states. The following tactics most often optimize economic returns and are recommended by the National Grasshopper Management Board:
Apply carbaryl (Sevin XLR1) at a rate of 8 fluid ounces per acre (=113 grams of active ingredient) with an equal volume2 of water at pH 7 in 100-foot swaths3, alternating with 100-foot untreated swaths (compared with the traditional approach of using 16 fluid ounces per acre in a blanket coverage).
Apply4 diflubenzuron (Dimilin 2L) at a rate of 0.75 fluid ounce per acre (=5.3 grams of active ingredient) with 8 fluid ounces of water and 4 fluid ounces of oil in 100-foot swaths3, alternating with 100-foot untreated swaths OR apply at a rate of 1 ounce per acre with 16 ounces of water and 8 ounces of canola oil5, in 100-foot swaths3 alternating with 200-foot untreated swaths (compared with the standard approach of using 1 fluid ounce per acre in a blanket coverage).
Apply malathion (Fyfanon) at a rate of 4 fluid ounces per acre (=138 grams of active ingredient) in 100-foot swaths3, alternating with 25-foot untreated swaths OR apply at a rate of 4 ounces per acre with 4 ounces of canola oil, in 100 foot swaths, alternating with 100-foot untreated swaths6 (compared with the traditional approach of using 8 fluid ounces per acre in a blanket coverage).
1 This RAAT method has been adopted in a 2EE label for most western states.
2 Increasing the volume of water above the 1:1 ratio with carbaryl will not improve, and may reduce, efficacy.
3 Facilitating droplet dispersal by using Micronaire nozzles or turning conventional nozzles angled 45 degrees into the wind may enhance efficacy. In addition, wider treated swaths (>100 foot) may be used. While it may be possible to proportionately expand untreated buffers, this approach has not been tested. Therefore, the most prudent tactic at this time would be to maintain the fixed widths of the untreated swaths.
4 Experimental applications have demonstrated that RAATs provides more than 90 percent mortality when ground temperatures exceed air temperatures by as much as 15 degrees Fahrenheit. Extensive research in Australia has demonstrated that when ground temperatures exceed air temperatures, thermals can limit insecticide deposition of aerial applications unless there are winds of 4 to 10 miles per hour (ideally, perpendicular to the swaths).
5 Using canola or corn oil, rather than crop oil, as a carrier may significantly improve the effectiveness of RAAT applications. Canola and corn oils are effective attractants and feeding stimulants for many rangeland grasshopper species.
6 Small-scale trials under optimal conditions indicate that 80 to 85 percent mortality also can be achieved using 100-foot swaths with the following rates and coverages: 5 fluid ounces per acre with 33-foot untreated swaths, 6 ounces with 50-foot untreated swaths, and 7 ounces with 100-foot untreated swaths.
Higher rates or coverages may be needed if: 1) treatments are applied to late instar nymphs (if using diflubenzuron), 2) ground temperatures exceed air temperatures (especially if using malathion), 3) grasshopper densities are extreme, 4) forage cover is tall or dense, or 5) terrain is rough. In all cases, grasshopper management software (CARMA or HOPPER1) should be used to assess a program. Apply insecticides in accordance with label directions and established guidelines for buffers around water, bees, and human habitations.
1Available from your USDA APHIS State Plant Health Director
For the preceding information in its original brochure form, view it in pdf format.If you don't have a pdf viewer, visit the Adobe website.
For a more complete treatment of RAATs, see: Decreasing Economic and Environmental Costs of Grasshopper Control
For a more complete treatment on canola oil as an attractant, see: Canola Oil as a Kairomonal Attractant of Rangeland Grasshoppers: an Economical Liquid Bait for Insecticide Formulation
For more information contact:
Dr. Alexander Latchininsky
Association for Applied Acridology International and
Department of Renewable Resources
University of Wyoming College of Agriculture
P. O. Box 3354
Laramie, WY 82071-3354
(307) 766-2298; latchini@uwyo.edu
