Evaluation of Marigolds and Entomopathogenic Nematodes for Control of the Cabbage Maggot Delia radicum

Abstract

The susceptibility of Delia radicum, cabbage maggot (CM), first instar larvae to fresh tissue extracts of two marigolds (Tagetes erecta and T. patula), the entomopathogenic nematode Steinernema feltiae, and a combination of them, was evaluated under laboratory and glasshouse conditions. In the laboratory, CM larvae were susceptible to marigold fresh tissue extracts; the root extracts were the most effective. Fresh root tissue extracts of non-flowering and flowering T. erecta caused 28% and 84% CM mortality, and T. patula caused 65% and 100% CM mortality, respectively. The nematodes caused up to 46% CM mortality at a concentration of 300 IJs/larva. In the glasshouse, up to 95% reduction of CM was achieved when cabbage plants, infected with CM eggs, were treated with fresh root extracts from either Tagetes species. Combination treatments with Tagetes and S. feltiae were also effective. Fresh tissue extracts of Tagetes spp. and S. feltiae show potential as control agents of D. radicum.

KEYWORDS:

• biological control
• cabbage maggot
• Delia radicum
• entomopathogenic nematodes
• marigold
• Steinernema feltiae
• Tagetes erecta
• Tagetes patula

The authors thank Dr. L. Lacey for providing the entomopathogenic nematodes; Ms. A. Dreves for providing the cabbage maggot pupae; the Washington State Pesticide Commission and the Chicona Family Fund /WSU Puyallup for funding C. Leger's M.Sc. project. E. Riga is supported by the College of Agricultural, Human, and Natural Resource Sciences Research Centre, PPNS No. 0428, Department of Plant Pathology and IAREC WSU-Prosser, Project No.WNP00542, Washington State University, Pullman, WA 99164-6430, USA.