Entomopathogenic nematodes for control of carrot weevil: efficacy and longevity in muck and mineral soils.

Background: Carrot weevil is an important pest throughout carrot-producing regions in Canada. Pesticides to control carrot weevil adults require application when the majority of adults have emerged and often this occurs after oviposition has already commenced and damage will be realized. One alternative to conventional pesticides are entomopathogenic nematodes. We studied four commercially available entomopathogenic nematode products (Steinernema feltiae, S. carpocapsae, S. kraussei and Heterorhabditis bacteriophora) for efficacy against carrot weevil in Nova Scotia and Ontario carrot fields in 2017 and 2018. The longevity and infectivity of the products in fine sandy loam soil (Ontario) and sandy loam soil (Nova Scotia) were evaluated using Galleria mellonella larvae.

Results: In Nova Scotia soils, only S. kraussei when applied twice, showed some efficacy to reduce damage from carrot weevil in 2017. In Ontario, an early application of H. bacteriophora and S. feltiae significantly reduced the percentage of carrots with weevil damage in 2018. Longevity and infectivity of S. carpocapsae and S. feltiae (against G. mellonella) was obtained up to 6 weeks post application in Nova Scotia in 2017. Similarly, S. feltiae showed infectivity up to 9 weeks post application in Ontario and Nova Scotia in 2018.

Conclusion: Entomopathogenic products showed an ability to survive and remain infective for up to 9 weeks in soils without irrigation. Timing of application to effect control of carrot weevil requires further study. The influence of soil moisture on the longevity and infectivity of these products is discussed. © 2021 Her Majesty the Queen in Right of Canada International Pest Management Science © 2021 Society of Chemical Industry. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.