Novel bacterial seed treatment protects wheat seedlings from insect damage

Insecticidal seed treatments are used commonly worldwide to protect seedlings against root feeding insects. Organophosphate insecticides that have been used for seed treatments are being phased out and replaced with neonicotinoid insecticides. Recent concerns about the environmental impact of neonicotinoids has prompted a search for alternatives. Microbial insecticides are a biological alternative for seed treatments to target root feeding insects. Six field trials with organophosphate (diazinon, chlorpyrifos), neonicotinoid (clothianidin) and microbial (Serratia entomophila) seed treatments targeting grass grub, a New Zealand scarab pest, were conducted in wheat crops at several sites over four years (2012-2015). Sites were selected each year that had potentially damaging populations of grass grub present during the trials. The insecticide and microbial treatments increased plant survival in all trials. Better plant survival resulted in higher yields from the organophosphate and neonicotinoid seed treatments from four of the six trials and neonicotinoid seed treatments gave similar yield increases to organophosphate treatments. Microbial treatment with S. entomophila resulted in higher yields for two of the six trials and for these two trials, the microbial treatment gave similar yield increases to the organophosphate and neonicotinoid treatments. Two trials at one site in 2014 and 2015 did not show any significant treatment effects at all, perhaps because grass grub populations were too low to cause yield losses. Seed treatment with S. entomophila is an alternative method for grass grub control however development of a commercial product requires effective scale-up of the production process and viability of the live bacteria needs to be maintained on coated seed.