Currently grass grub larvae are predominantly controlled using organophosphate insecticides, which while very effective at controlling grass grub larvae, are of high risk to human health. Thus, following reassessment by the Environmental Protection Agency (EPA) in 2013, many products are being phased out. The second chemical group commonly used to control grass grub are those in the neonicotinoid family, which includes Poncho® and Gaucho®. These products provide repellency and killing activity against grass grub larvae and are considered to be of low toxicity to humans. However, there is much international interest in this family from issues associated with honey bee health.
So where is the future of grass grub control?
Three seasons ago FAR and AgResearch, with funding from MPI SFF, began field trials investigating methods for reducing the reliance on organophosphate chemistry. Rapid knockdown will be difficult without access to organophosphate insecticides, so growers will need to be proactive, noting when and where grass grub infestations have been located in the previous season.
Over three years, three different biocontrol options were investigated for use in the protection of wheat seedlings from attack by grass grub larvae. When used as a seed treatment, FAR 11/01 has provided adequate protection in two of three seasons when tested as a seed treatment. FAR 11/01 produced grain yields similar to Poncho in two seasons, while in the first season the treatment appeared to reduce seedling vigour, thus grain yield achieved was intermediate when compared to the untreated and Poncho. FAR 11/02 was an experimental granular formulation used in various combinations and timing, but this treatment has not performed as well as FAR 11/01. The third product (FAR 14/01) involves a novel micro-organism and has shown promise in the single season it has been tested, where results similar to Poncho were achieved.
Overall, potential options have been identified that may provide a new method of controlling grass grub in arable cropping systems.