Scarabaeidae
Pest description and crop damage Robust, C-shaped larvae of June beetles, 0.125 to 1.25 inches long, with a brown head capsule and prominent jointed legs. The body is an overall dirty white, but the last abdominal segments are blue-black internally. Damage from larval feeding appears as severed (cut) taproots in early season and as surface cavities on taproots later during the season.
Infestations are most likely when sugar beets follow grassy pastures. Grasses are the preferred host plants both for oviposition and larval feeding. Some species require two or more years for egg-to-adult development, so old pasture can be infested with substantial populations of last-stage (large) grubs that are especially damaging to seedling sugar beet plants. White grubs are rarely a problem in sugar beet fields that do not follow grassy pastures.
Scouting and thresholds No formal economic thresholds exist for white grub insecticide treatment decisions. If following pasture with sugar beets, examination of soil for larvae before planting can inform the need for at-plant insecticides.
Management-biological control
Microbial biopesticides are available (Table 3).
Management-chemical control
Several at-plant and post-emergence insecticides are available (Tables 1-2).