Billbug resistance also occurs in many perennial ryegrass cultivars, particularly those that contain endophytic fungi. Biological controls include predation by birds and hunting wasps, fungal diseases and parasites. See fact sheet 5.573, insect Parasitic Nematodes . The nematodes are available from many mail order suppliers and several nurseries. Young larvae are protected within the plant.
Older larvae occur in the root zone where insecticides fail to penetrate.
Best control for the bluegrass billbug occurs when sprays are applied in early May to kill adult Insects prior to egg laying. Current information on the Denver billbug indicates that a slightly later timing, in early June, is more appropriate. Apply adult sprays so insecticide residues remain as long as possible on foliage and in the crown area of the plant. This may be achieved better with liquid sprays than with granular formulations. White grubs are the most damaging Insects in Colorado lawns along the Western Slope, in the Arkansas Valley, and through much of the Eastern Plains.