Bioassays of acaricides with twospotted spider mite
PI(s): Herbert, Jr, David Ames, Ashley, Janet L, Lewis, Ed E, Huckaba, Randy
Investigators:
Abstract: Management for twospotted spider mite, Tetranychus urticae Koch, populations in peanut, Arachis hypogaea L., relies on acaricides. The outcomes of acaricide applications are most predictable when complete information on their toxicity and specificity is available. Specifically, the degrees to which acaricides impact different stages of T. urticae and natural enemies combined determine the overall efficacy of an acaricide application. The objectives of this study were to determine stage-specific direct and residual efficacies of three acaricides (fenpropathrin, etoxazole, and propargite) against T. urticae, and the direct and residual toxicity of the acaricides to Orius insidiosus (Say) adults. Direct toxicity of acaricides to T. urticae was measured on peanut cuttings. All acaricide treatments caused significant mortality to a mixed stage population of T. urticae, and mortality did not differ among the acaricides 7d after treatment. When toxicity to eggs was tested, the proportion of eggs that hatched for all acaricide treatments was significantly lower than the control, with etoxazole and propargite causing 100% mortality. Exposure to acaricide residues caused 30% mortality of T. urticae adults 1 and 2 d after treatment and was not significantly different from the control. Fenpropathrin and propargite caused 100% mortality and etoxazole caused 50% mortality of O. insidious adults after direct exposure to the acaricides. Residual toxicity of acaricides to O. insidiosus adults varied but remained toxic to O. insidiosus longer than to T. urticae. Fenpropathrin had the longest residual effect on O. insidiosus adults, causing 95% mortality after 14 d; etoxazole and propargite caused 30% mortality after 14 d.
Description:
The information gained from this study can be used to improve recommendations made to growers about the management of T. urticae in field crops such as peanut. Instead of relying on one acaricide to manage T. urticae infestations, as is commonly done, we propose that the timely application of a stage- and target specific acaricide may prove to be a more effective strategy. Because there are always eggs, immatures, and adults present in a naturally occurring infestation of T. urticae, the use of an adulticide alone will not effectively manage the mites. It would be more appropriate to apply an acaricide, such as proparigite, which is highly toxic to a mixed population of T. urticae in the early stages of the crop cycle when populations of beneficial species such as O. insidiosus are usually low. The residual effect of proparigite will be short, so a second spray of an ovicide such as etoxazole could potentially be used to effectively suppress T. urticae with less harm to beneficial species.
Commodities: Peanuts
Resources: Agricultural Experiment Station Facilities
Disciplines: Integrated Pest Management
Audiences: Agribusiness, Commodity Groups, Extension Agents, Producers, Researchers
