Western spotted cucumber beetle (Diabrotica undecimpunctata)
Pest description and crop damage The adult of the corn rootworm, also known as the western spotted cucumber beetle, is yellowish green, 0.25 inch long, and has 11 black spots on its wing covers. Mature larvae are white, except for the head and last abdominal segment, which are brown. They are about 0.62 inch long. The larvae appear to have two heads.
Corn rootworm adults eat small holes in the leaves of emerging corn plants. They lay their eggs at the base of emerging corn plants. Larvae attack the roots of the corn seedlings. Occasionally, larvae cause significant stand losses in early corn plantings. Adults feed on corn silk and may have an impact on pollination, though this has not been evaluated fully in the PNW.
Pest Monitoring It is rare to treat emerging sweet corn to prevent foliar damage by adults. However, if adult feeding damage is observed in emerging sweet corn, this may indicate significant egg laying pressure. If this occurs at corn emergence in an unprotected corn planting, post-emergence insecticide treatment may be justified. No action threshold has been established. Observations indicate that noticeable damage may occur to developing corn ears prior to harvest when populations reach two adult beetles per ear.
Home gardeners: In most years, beetle populations diminish after egg laying and prior to the emergence of the summer population. Seeding can be delayed until after the beetles have dispersed and deposited most of their eggs. Individual beetles can be picked off.
Management-chemical control: HOME USE
- bifenthrin (as a mix with zeta-cypermethrin).
- horticultural oil- Some formulations are OMRI-listed for organic use.
- pyrethrins-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- acetamprid (Assail 30SG) at 0.075 to 0.1 lb ai/A. PHI 7 day. REI 12 hr. Limit 2 treatments per year. Retreatment interval 14 days. Do not exceed a total of 0.21 lb ai/A per growing season.
- alpha-cypermethrin (Fastac EC) at 0.014 to 0.025 lb ai/A. PHI 3 days. REI 12 hr. Retreatment interval 3 days. Do not exceed 0.075 lb ai/A per season.
- beta-cyfluthrin (Baythroid XL) at 0.013 to 0.022 lb ai/A. PHI 0 days. REI 12 hr. Retreatment interval 2 days. Do not exceed a total of 0.22 lb ai/A per growing season.
- bifenthrin (Capture LFR) at 0.033 to 0.1 lb ai/A. PHI 1 day. REI 12 hr. Do not exceed 0.2 lb ai/A per season.
- bifenthrin/zeta-cypermethrin (Hero) at 0.04 to 0.1 lb ai/A. PHI 3 days. REI 12 hr. Retreatment interval 3 to 5 days. Do not exceed 0.266 lb ai/A per season.
- carbaryl (Sevin 4F) at 1 to 2 lb ai/A. PHI 2 days for harvest of ears, 14 days for forage, 48 days for fodder. REI 24 hr. Do not exceed 16 lb ai/A per year. Retreatment interval 3 days. Limit 8 treatments per year.
- deltamethrin (Delta Gold) at 0.018 to 0.028 lb ai/A. PHI 1 day. REI 12 hr. Do not apply more than 0.45 lb ai/A in one growing season.
- chlorantraniliprole/lambda-cyhalothrin (Besiege) at 0.06 to 0.1 lb ai/A. PHI 1 day. REI 24 hr. Retreatment interval 1 day. Do not exceed 0.48 lb ai of lambda-cyhalothrin or 0.2 lb ai of chlorantraniliprole per acre per growing season.
- esfenvalerate (Asana XL) at 0.03 to 0.05 lb ai/A. PHI 1 day. REI 12 hr. Do not exceed 0.5 lb ai/A per year.
- GS-omega/kappa-Hxtx-Hv1a (Spear Lep) at 0.8 lb ai/A. PHI 0 days. REI 4 hr. Do not exceed 2 lb ai/A per year.
- lambda-cyhalothrin (Warrior II) at 0.02 to 0.03 lb ai/A. PHI 1 day. REI 24 hr. Do not exceed 0.48 lb ai/A per year. Retreatment interval 4 days. Do not harvest for feed or graze livestock for 21 days.
- malathion (Drexel Malathion 5EC) at 1.0 lb ai/A. PHI 5 days. REI 12 hr. Retreatment interval 5 days. Limit 2 treatments per year.
- methomyl (Lannate SP) at 0.23 to 0.45 lb ai/A. PHI 0 days for ears, 3 days for forage, and 21 days for stover. REI 48 hr. Do not exceed 6.3 lb ai/A per season.
- permethrin (Ambush 25WP, Pounce 25WP) at 0.1 to 0.2 lb ai/A. PHI 1 day. REI 12 hr. Retreatment interval 5 days. Do not exceed 1.2 lb/A Ambush or 0.8 lb ai/A Pounce per season.
- zeta-cypermethrin (Mustang) at 0.028 to 0.05 lb ai/A. PHI 3 days. REI 12 hr. Do not exceed 0.3 lb ai/A per season. Retreatment interval 3 to 5 days.