Development of Management Programs for White Grubs in California Blueberries

Abstract

During the past few years, white grubs have become recognized as a pest of southern highbush blueberries in California. White grubs feed on plant roots causing the plant to be stunted. In some cases, plant death has occurred when large grub populations attack newly planted fields. The predominant white grub species in California blueberries was identified as Cyclocephala longula. Research on flight characteristics determined that grubs are primarily in the third instar in April, pupate in May, and fly from mid-June through mid-July. Egg hatch begins in mid-July. Adult beetles begin flying about 30 min after dark and can be collected for a period of about 2 hours with black-light traps. Evaluation of control methods found that the entomopathogenic nematode Heterorhabditis bacteriophora and the insecticide imidacloprid can both provide control of the grub. Applications of Heterorhabditis bacteriophora on April 1 initially only provided 8.3% control, but resulted in secondary spread that led to an epizootic within the grub population. Applications of Heterorhabditis bacteriophora and imidacloprid in August resulted in 81.6 and 71.1% control, respectively, the following June.

Keywords:

• grubs
• Cyclocephala
• entomopathogenic nematodes
• Heterorhabditis bacteriophora
• southern highbush blueberry

ACKNOWLEDGEMENTS

We wish to thank grower-cooperators John Ojalla, Misty Rex, and Bruce Frost, for their assistance in providing field locations and in-kind donations that made this project possible. We also wish to thank Dr. Harry Kaya and Dr. Edwin Lewis for providing advice that focused this project in a positive direction that could quickly provide critical information that would lead to a management program for blueberry farmers.