TOLERANCE OF COOL-SEASON TURFGRASSES TO FEEDING BY JAPANESE-BEETLE AND SOUTHERN MASKED CHAFER (COLEOPTERA, SCARABAEIDAE) GRUBS

Response of Kentucky bluegrass, Poa pratensis L.; tall fescue, Festuca arundinacea Schreber; hard fescue, F. ovina L. var. duriuscula; peren nial ryegrass, Lolium perenne L.; and creeping bentgrass, Agrostis pal ustris (Hudson), to herbivory by root-feeding by grubs of Japanese bee tle, Popillia japonica Newman, and southern masked chafer, Cyclocephal a lurida Bland, was evaluated in greenhouse trials. Potted turfgrasses were infested with initial densities equivalent to 73 or 146 grubs pe r 0.1 m(2) in spring and fall trials, and effects on plant growth and grub survival were determined. All turfgrasses tolerated significant d amage to roots without loss of foliage yield. In fact, feeding by grub s stimulated increased growth of foliage in some grasses. With compara ble densities of grubs, loss of roots tended to be proportionately les s in creeping bentgrass than in other grass species. Survival of grubs was similar in all turfgrasses, and between low and high grub densiti es. P, japonica caused greater loss of roots than C, lurida in the spr ing trial, but the reverse was true in the fall. Root loss per grub de creased with increasing larval density, suggesting food limitation eve n though root systems were not completely devoured. Implications of th ese findings for tolerance and recovery of grub-damaged turfgrasses ar e discussed.