Silicon fertilization to induce resistance to annual bluegrass weevil in annual bluegrass and creeping bentgrass

The annual bluegrass weevil (ABW), Listronotus maculicollis Kirby, is a devastating and difficult-to-manage turfgrass insect that primarily damages short-mown annual bluegrass, Poa annua, and creeping bentgrass, Agrostis stolonifera. Silicon (Si) accumulation in plants, specifically in grasses, is a potent defense against insect herbivores. Plant roots take up Si from the soil solution as monosilicic acid, which is further transported to the shoot via xylem and deposited in and around tissues as amorphous hydrated silica or phytoliths. Silicification makes tissues abrasive and tougher and reduces the digestibility and palatability of tissues to insect herbivores and thus enhancing plant resistance to insects. Although the role of Si against chewing insects is well-documented, no previous studies, to our knowledge, have investigated its impacts on the survival, development and performance of the ABW. We conducted glasshouse and field experiments to investigate how Si fertilization of annual bluegrass and creeping bentgrass affects ABW and impacts plant tolerance to ABW herbivory. We found that Si fertilization of annual bluegrass reduced ABW egg-laying by 7-16% and larval numbers by 0-30% but did not impact the rate of larval development. In creeping bentgrass, Si reduced ABW egg-laying by 15-25% and larval numbers by 20-52% and delayed larval development. The stronger negative effects of Si against ABW on creeping bentgrass could benefit it to outgrow annual bluegrass in mixed stands. Given that annual bluegrass is often considered a problematic weed in creeping bentgrass fairways, Si fertilization thus could turn ABW into a biological weed control agent.