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.
Scouting and thresholds No formal economic thresholds exist for white grub insecticide treatment decisions. There are no effective "rescue" treatments that can be applied postemergence in sugar beets for white grubs.
Management-biological control
- Beauveria bassiana (BotaniGard 22WP, BotaniGard ES, Mycotrol ESO, Mycotrol O, Mycotrol WPO - live spores of an insect-killing fungus; various strains)-See label for rates. PHI 0 days. Typically requires 7 to 10 days after first spray to see control. Begin treatment at first appearance of pest. Reapply as necessary.
Management-chemical control
- alpha-cypermethrin (Fastac CS)-at-planting application at 0.025 lb ai/A. Apply in a 3- to 4-inch T-band over the open furrow at planting in a minimum of 3 to 5 gal/Acre. PHI 50 days.
- pyrethrins/Beauveria bassiana (BotaniGard Maxx, Xpectro OD)-See label for rates. Do not reapply for at least 3 days. In case of extreme pest pressure, wait a minimum of 24 hr before reapplying. Do not harvest until spray has dried.
- terbufos (Counter 20G Lock'n Load, Counter 20G Smartbox) at 0.6 to 1.2 oz ai/1,000 row ft banded at planting. Apply in 5- to 7-inch band over the row and lightly incorporate. One application per year. Do not place granules in direct contact with the seed. Do not exceed 2 lb ai/A. -or- Apply at 0.6 to 1.2 oz ai/1,000 row ft, modified in-furrow at planting. Apply in furrow, 2 to 3 inches behind seed drop zone after some soil has covered the seed. One application per year. Do not place granules in direct contact with the seed. Do not exceed 2 lb ai/A.
- thiamethoxam (Cruiser 5FS)-Application only by commercial seed treaters; no on-farm seed-treatment application.
- zeta-cypermethrin-
- (Mustang) at 0.05 lb ai/A planting application. Apply in furrow or in a T-Band (band over open furrow) in a minimum of 3 to 5 gal/A water. PHI 50 days. Do not apply more than 0.15 lb ai/A per season (at planting/foliar applications).
- (Mustang Maxx) at 0.025 lb ai/A planting application. Apply in-furrow or make a 3- to 4-inch T-Band at planting in a minimum of 3 to 5 gal per acre. PHI 50 days for tops or roots. Do not apply more than 0.075 lb ai/A per season. REI 12 hr.