Cultural practices affect root-feeding white grubs (Coleoptera: Scarabaeidae) in turfgrass

Cultural practices were manipulated before or during seasonal flights of Japanese beetle, Popillia japonica Newrnan, and masked chafers, Cyclocephala spp., to study effects on grub densities in tall fescue or Kentucky bluegrass turf. Masked chafer grubs were consistently smaller and less abundant in turf that had been treated with aluminum sulfate to reduce soil pH and in high-mown turf. High mowing or application of aluminum sulfate before beetle flights reduced total biomass of white grubs in tall fescue by as much as 55 and 77%, respectively. However, where spatial gradients in soil moisture occur, the positive response of grub populations to moisture may override effects of those treatments. Grub densities were not affected by spring applications of lime or urea or by aerification of plots before beetle nights. Plots that were irrigated during beetle flights incurred significantly higher densities of both P japonica and Cyclocephala spp. grubs than did nonirrigated turf. The use of a 2,247-kg roller to compact the soil before beetle flights did not affect subsequent grub populations, and the roller was not effective for remedial control of 3rd instars in the fall. Application of organic fertilizers (composted cow manure or activated sewage sludge) resulted in significant increases in grubs of green June beetle, Cotinis nitida L., in 1 of 2 yr. Cultural practices may have general or species-specific effects on densities of white grubs. This study suggests that witholding irrigation during peak flight of beetles, raising cutting height, and light application of aluminum sulfate in spring may help to reduce the severity of subsequent grub infestations.