Serratia entomophila-coated seed to improve ryegrass establishment in the presence of grass grubs

Abstract

The entomopathogenic bacterium, Serratia entomophila, is an alternative to chemical control of grass grub (Costelytra zealandica) and is applied in a granule formulation to established pastures. Treatment of seed with microbial inoculants is an ideal mechanism for delivery and establishment of microbial control agents into the plant root zone where soil dwelling pests, such as grass grub, are located. Seed treatment with S. entomophila was tested in three glasshouse pot trials, for its ability to protect germinating ryegrass seedlings from grass grub damage. A range of larval densities was used and microbial seed treatment was compared with the insecticide imidacloprid. At medium larval densities (equivalent to 70 larvae/m2), use of S. entomophila-coated seed resulted in 85% seedling establishment in comparison with 82% emergence from imidacloprid-treated seed. At a high larval density of 300/m2, where there was no establishment of untreated seed, 35-51% of seedlings established from S. entomophila-treatead seed. Results suggest there is potential for seed coating to aid ryegrass establishment in autumn-sown pastures.