Irrigation and Nitrogen Fertilization Effects on White Grub Injury to Kentucky Bluegrass and Tall Fescue Turf

Abstract

Root‐feeding white grubs (Coleoptera: Scarabaeidae) are important pests of cool‐season turfgrasses in the eastern USA. We studied effects of irrigation and N fertilization on Kentucky bluegrass (Poa pratensis L.), and tall fescue (Festuca arundinacea Schreb.) response to grub damage under greenhouse and field conditions. Potted turfgrasses, with or without Japanese beetle (Popillia japonica Newman) grubs (122/0.1 m2), were maintained under two irrigation regimes, with or without supplemental N fertilizer (204 kg N ha−1). Foliar and root yields, and grub survival were measured after 4 wk. In the field, sod was grown in rooting boxes, with or without spring fertilization (146 kg N ha−1) and fall irrigation (2.54 cm wk−1). Half of the plots were infested with southern masked chafer (Cyclocephala lurida Bland) grubs (66 /0.1 m−1) in late August and effects on aesthetic damage, surface temperature, foliar yield, root strength, and grub survival were measured for 9 wk. Grubs severely damaged roots of both grasses regardless of management regime. Within regimes, however, this damage significantly reduced follar yield only in turf that received both N and high irrigation. In the greenhouse, grub‐damaged grasses that received remedial N, nevertheless, had higher foliar yield than did non‐fertilized grasses without grubs. In rooting boxes, fall irrigation following spring fertilization enhanced visual quality of grub‐infested turf and root strength of grub‐damaged Kentucky bluegrass. Survival of grubs did not differ between grass species or fertilization regimes, but more P. japonica survived in pots receiving high irrigation. Irrigation during the fall feeding period, followed by remedial N fertilization, may promote tolerance and recovery of grub‐damaged turfgrasses.