Influence of the application methods and doses on the susceptibility of black vine weevil larvae Otiorhynchus sulcatus to Metarhizium anisopliae in field-grown strawberries.
Entomopathogenic fungi are commercially available for the control of insect pests, including the black vine weevil (BVW) Otiorhynchus sulcatus Fabricius (Coleoptera:Curculionidae). However, Metarhizium anisopliae (Metsch.) Sorokin (Clavicipitaceae) has not been used to control BVW in field-grown strawberries. Field trials were conducted in different locations in the UK during 2009-2010 to evaluate the different formulations (granular vs. drench) and application methods (premixed, drench, bare root treatment) of commercial strain of M. anisopliae Met52® (=F52), the entomopathogenic nematodes and the organophosphate insecticide Cyren® against BVW. The highest dose (1014 cfu ha-1) tested provided significantly better control than the intermediate (1013 cfu ha-1) or low (1012 cfu ha-1) doses. BVW larval control at the high, intermediate and low doses was 71-96, 40-75 and 6-11%, respectively. Premixing, drench or bare root treatment with Met52® gave similar levels of BVW control. Irrespective of the application methods or soil types, the high dose rate of Met52® provided the best control. Significantly high larval control was achieved (78-97%) when chlorpyrifos was applied at planting than eight weeks post planting (53%). There were significant differences in BVW control between Met52® (88%) and reduced doses of Heterorhabditis bacteriophora Poinar (20-29%) or Steinernema kraussei Steiner (39-75%) when applied alone. However, when used together, low dose of S. kraussei and Met52® provided 100% control of BVW larvae. This study shows that Met52® has considerable potential for the control of BVW larvae in commercial field-grown strawberry, thereby offering an environmentally benign alternative to chemical insecticides.