ARS | Publication request: A comparison of application methods for suppressing the pecan weevil (Coleoptera: Curculionidae) with Beauveria bassiana under field conditions

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 29, 2007
Publication Date: March 20, 2008
Citation: Shapiro Ilan, D.I., Gardner, W.A., Cottrell, T.E., Behle, R.W., Wood, B.W. 2008. A comparison of application methods for suppressing the pecan weevil (Coleoptera: Curculionidae) with Beauveria bassiana under field conditions. Environmental Entomology. 37:162-171.

Interpretive Summary: The pecan weevil is a key pest of pecans. The fungus Beauveria bassiana is an environmentally friendly natural biopesticide that is capable of killing insects such as the pecan weevil. One approach to controlling the weevils may be application of the fungus directed toward adult weevils as they emerge from the soil to attack nuts in the tree canopy. Our objective was to compare different application methods for suppression of pecan weevil. We compared direct application of the fungus to the to soil under the tree canopy, soil application followed by cultivation, soil application in conjunction with a cover crop (Sudan grass), direct application to the tree trunk, and application to the trunk with an ultra-violet radiation protecting adjuvant. The study was conducted in a pecan orchard in Byron, GA, in 2005 and 2006. On average weevil mortality was greater in all treatments than in the non-treated control in 2005 and 2006; > 75% average mortality was observed with the trunk application both years, and in the trunk application with UV protection in 2005. Results indicated trunk applications can produce superior efficacy relative to ground application, particularly if the ground application is followed by cultivation. Efficacy in the cover crop treatment, however, did not differ from other application approaches. The fungus application appears promising, but future research should focus on the extent to which B. bassiana induced weevil mortality reduces crop damage.

Technical Abstract: The pecan weevil, Curculio caryae (Horn), is a key pest of pecans. The entomopathogenic fungus Beauveria bassiana is pathogenic to C. caryae. Our objective was to compare different application methods for suppression of C. caryae adults. Treatments included direct application of B. bassiana (GHA strain) to soil under the tree canopy, soil application followed by cultivation, soil application in conjunction with a cover crop (Sudan grass), direct application to the tree trunk, and application to the trunk with an ultra-violet radiation protecting adjuvant. The study was conducted in a pecan orchard in Byron, GA, in 2005 and 2006. When averaged over the 15 d sampling period, weevil mortality and signs of mycosis were greater in all treatments than in the non-treated control in 2005 and 2006; > 75% average mortality was observed with the trunk application both years, and in the trunk application with UV protection in 2005. Results indicated trunk applications can produce superior efficacy relative to ground application, particularly if the ground application is followed by cultivation. Efficacy in the cover crop treatment, however, did not differ from other application approaches. Future research should focus on the extent to which B. bassiana induced C. caryae mortality reduces crop damage.