Efficacy of Metarhizium anisopliae as a Curative Application for Black Vine Weevil (Otiorhynchus sulcatus) Infesting Container-Grown Nursery Crops

Abstract

Abstract The black vine weevil (BVW), Otiorhynchus sulcatus (F.) is a serious pest of nursery crops. The fungus, Metarhizium anisopliae (F52), is registered by the U.S. Environmental Protection Agency for BVW control. The objectives of this study were to determine the efficacy of a curative drench application of M. anisopliae for controlling BVW larval infestations in container-grown nursery plants and the effect of temperature on the rate of fungal growth and speed of kill. Trials evaluating the efficacy of M. anisopliae as a curative application were performed in the spring of 2004 and 2005 as well as the fall of 2006. Laboratory studies were performed to quantify the impact of temperature (10, 15, 20, 24 and 28C) on fungal growth and speed of kill. Metarhizium anisopliae applied in the greenhouse and outdoors in 2004 were 92 and 30% effective, respectively. Fungal applications to container-grown plant material maintained outdoors in the spring of 2005 were nearly 100% effective 28 days after application. Fall applications in 2006 provided statistically significant reductions in the number of live BVW larve per pot, but were not as effective as spring applications in 2005. The mean media temperature of containers maintained outdoors in the fall of 2006 dropped considerably (10–12C) over the course of the experiment and were likely the cause for the reduced efficacy. Laboratory experiments demonstrated that temperatures below 20C (68F) significantly slowed fungal growth and the speed at which M. anisopliae infected BVW larvae. In the field, drench applications of M. anisopliae were very effective at eliminating BVW larvae in container-grown nursery plants when media temperatures were adequate (> 15C (59F)). The use of M. anisopliae as a curative drench application has similar temperature-dependent limitations as the use of entomopathogenic nematodes for BVW control. Therefore, applications should occur as early in the fall as possible once egg laying has ended or in late spring just prior to pupation when media temperatures would be most conducive to fungal infection.