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


Blatt, S, McDonald, MR and Mlynarek, J. 2021. Entomopathogenic nematodes for control of carrot weevil: efficacy and longevity in muck and mineral soils. Pest Management Science

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Entomopathogenic nematodes (EPNs) feed upon insects living in the soil. EPNs occur in all soils throughout the globe and their use for pest management has been explored since the 1930s. Specific species of these EPNs have been developed into commercial products, but their use in field agriculture has not been well studied. Our work explored the potential of four commercially available EPN products to manage carrot weevil, a serious pest of carrot throughout Canada. Products were sourced from BioBest and were 4 species of EPN: Steinernema feltiae (Steiner System), S. kraussei (Kraussei System), S. carpocapsae (Carpo System) and Heterorhabditis bacteriophora (B-Green System). These products were tested in Ontario on muck and fine sandy loam soils and in Nova Scotia on mineral soils. Products were applied at label rates to plots (3 beds wide and 5 m long) with treatments replicated at least 5 times in 2017 and 2018. In 2017 we tested whether 1 or 2 applications of the products would reduce damage from carrot weevil and in 2018 we tested various application timings to determine the optimal time to target carrot weevil. In both years we sampled some of the plots at weekly intervals, brought the soil samples to the lab and placed waxworms on the surface. After 1 week we dissected the waxworms for evidence of EPNs. We did this to determine how long the products persisted in the soil and their ability to infect the waxworms. When we sampled the plots we also measured the soil moisture so we could determine whether these EPNs would survive under field conditions. Soil moisture is important for EPN survival and many field crops in Nova Scotia are not irrigated. We found some evidence that S. kraussei (Kraussei System) when applied twice would reduce damage from carrot weevil in 2017. The cost of the EPN products is such that a grower applying these products twice to a field would not be cost-effective. In 2018, early applications of H. bacteriophora (B-Green System) and S. feltiae (Steiner System) did reduce damage from carrot weevil in southern Ontario. EPN products did show excellent longevity and infectivity in both mineral (in Nova Scotia) and fine sandy loam (in southern Ontario) soils, showing survival and infectivity for 6 and 9 weeks, NS and ON, respectively. These results are encouraging as soil moisture levels during the study were well below 10%. Further study on the best timing of the applications is warranted to fully evaluate EPN products for control of agricultural pests in Nova Scotia and Ontario.


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 is entomopathogenic nematodes. We studied four commercially available entomopathogenic nematode products (Steinernema feltiae, S. carpocapsae, S. kraussei andHeterorhabditis bacteriophora) for efficacy against carrot weevil in Nova Scotia and Ontario carrot fields in 2017 and 2018. 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 ability to survive and remain infective 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.

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