Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2002
Publication Date: 12/1/2003
Citation: Cottrell, T.E., Wood, B.W. 2003. Pecan weevil management: past, present and toward a future strategy. Southwestern Entomologist. 27:75-84.
Interpretive Summary: The pecan weevil is a serious threat to economic pecan production throughout most pecan-producing regions. Conventional airblast application of carbaryl is very effective for pecan weevil control. However, application of carbaryl to the canopy destroys populations of beneficial insects and can result in outbreaks of aphid and mite populations, thus requiring further pesticide applications. Control of weevils may be achieved when weevils crawl up the pecan trunk. We applied various rates of carbaryl to pecan trunks and exposed weevils to those trunks (at 1, 4, 8, and 13 days after insecticide application) for a single, brief interval. If effective, future pecan weevil management programs may include such a strategy since natural enemies in the canopy would be less-affected and applications would be targeted to a specific site. Brief exposure to the insecticide on the trunk affected pecan weevils. Data indicates that to achieve 95% weevil mortality by 12 h after exposure and through 13 days after treating trunks, carbaryl would need to be applied to trunks at a rate of 7.9× the rate of carbaryl normally applied to foliage. It is likely that other insecticides may also prove effective if used in this manner.
Technical Abstract: The pecan weevil is an indigenous pest of the native North American pecan. Before the era of broad-spectrum chemical insecticides, management of the pecan weevil was attempted with cultural methods, but control was generally poor. Chemical insecticides offered efficacious foliar sprays and a few soil treatments but most are no longer available. Carbaryl has emerged as the predominant insecticide presently used to manage pecan weevils. We tested carbaryl, applied to pecan trunks at various rates, against weevils that were exposed to those trunks for a single, brief interval 1, 4, 8 and 13 days after treating trunks; each individual was evaluated as healthy, moribund or dead at 3, 6, 12, 24, 48 and 72 h after exposure. Probit analysis was used to estimate effective rates that resulted in 95% non-feeding weevils (i.e., ER95) for the four test dates after application and six time periods after exposure. A regression equation in terms of days since insecticide application and hours since exposure was fit to those estimates and used to construct a response surface plot. Brief exposure to the insecticide affected pecan weevils. Data from the plot indicates that to achieve an ER95 by 12 h after exposure and through 13 days after treating trunks, carbaryl would need to be applied at a rate of 7.9× the rate of carbaryl normally applied to foliage. It is likely that other insecticides may also prove effective when used in this manner.