Rhizobacterial treatments of tall fescue and bermudagrass increases tolerance to damage from white grubs

Background Inoculation of hybrid bermudagrass with plant growth‐promoting rhizobacteria (PGPR) can increase plant growth and influence relationships with above‐ground herbivores like fall armyworms. However, few experiments have evaluated PGPR applications relative to root herbivory. Root‐feeding white grubs cause severe damage to grasses, especially in tall fescue pastures, golf courses, and lawns. Since bacterial inoculants enhance root growth, the goal of this study was to determine if the inoculation of hybrid bermudagrass by rhizobacteria can increase the tolerance of tall fescue and hybrid bermudagrass to damage from white grub feeding, and if PGPR are compatible with neonicotinoid insecticides commonly used for white grub control. Results In trials with tall fescue and hybrid bermudagrass, grasses were treated with the PGPR strain mixture Blend 20 or nitrogen or left non‐treated and were then infested with Japanese beetle grubs. Grasses treated with PGPR and nitrogen fertilizer produced significantly more top growth than the non‐treated grub‐infested controls. Tall fescue and hybrid bermudagrass treated with Blend 20 produced root mass similar to or greater than nitrogen fertilized grasses. Both grasses treated with Blend 20 had greater root mass than non‐treated infested grass. No treatment negatively impacted grub survival, and weight gains of grubs were similar for all treatments. Bacterial strains were typically compatible with insecticides used to control white grubs. Conclusion PGPR and nitrogen fertilization stimulate root growth resulting in tolerance of tall fescue and hybrid bermudagrass to white grub infestation. PGPR, acting as biostimulants to increase root biomass on grasses, may have utility for IPM of root herbivores. © 2019 Society of Chemical Industry