Billbugs

The Phoenix and hunting billbug adults are dark brown and light brown, respectively. Both are 0.33 inch long weevils (snout beetles) with a long, downward-pointing snout and elbowed, clubbed antennae. The Phoenix billbug is more common in California than the hunting billbug. The hunting billbug can be identified by a Y-shaped marking on the thorax with separate, inward-facing marks that resemble parentheses on either side of the Y. These two marks in the Phoenix billbug combine to form an M. Adults are often seen walking on paved areas, but are difficult to find on golf courses unless a drench test is used. Eggs are inserted into the turfgrass stems. They hatch about 6 to 8 weeks after adults first appear. Larvae are creamy white, legless, and somewhat hunch-backed, C-shaped grubs with a brown head. The lack of legs distinguishes billbug grubs from white grubs. Adults may be found all year round.

Although all species of turfgrass can be attacked, serious damage is seen primarily on bermudagrass and zoysiagrass. Zoysiagrass is preferred by hunting billbugs while phoenix billbugs prefer bermudagrass.

Billbug larvae first feed on the inside of the turfgrass stem and crown, then move into the soil where they feed on roots. Fine, whitish, sawdustlike larval excrement (frass) can be observed on the soil surface. Billbug larvae feed higher up on the roots than white grubs, so billbug-damaged turf is easier to pull from the soil than that damaged by white grubs because it breaks at the crown. Billbugs may feed on roots to a depth of 3 inches; however, unlike turf damaged by white grubs, damaged turf cannot be rolled back like a carpet and the soil does not feel spongy underfoot. Turfgrass planted on fumigated soil is especially susceptible to damage because of the loss of natural enemies. Drought-stressed turfgrass may be severely impacted.

Where possible choose resistant varieties of bermudagrass and zoysiagrass or other less susceptible turf species. Perennial ryegrasses with endophyte fungal enhancement are resistant to billbug attack and can be used to overseed in fall. Good irrigation, fertilizing, and mowing practices may allow turf to tolerate low levels of billbugs.

If you suspect a billbug infestation, look for piles of fine frass at the base of turfgrass plants. In areas where frass or damage is evident, dig up the turfgrass to look for grubs. (For more information on monitoring, see MONITORING AND TREATING INSECTS AND MITES. Commercially available nematodes, Steinernema carpocapsae or Heterorhabditis bacteriophora, often control billbug larvae, especially in sod farms or other locations where the soil has been fumigated. Apply nematodes to moist turf and irrigate following application of either nematodes or chemical insecticides to move the material into the zone of larval feeding activity.

With overlapping generations and a long season in California, billbugs are difficult to control with insecticides. Preventive grub materials (imidacloprid, thiamethoxam) are quite effective, but must be applied before eggs are laid and damage detected. They kill the next generation of young larvae. Curative treatment of billbug grubs with currently available insecticides is difficult.