Pest description and crop damage Redbacked cutworm (RBC) is a key pest of mint east of the Cascades. As mint begins to send up aerial growth in the spring, larvae feed underground by day, clipping off new spring shoots at or below ground level. At night, larvae feed on and above the soil surface. In some years, damage to mint during May and early June in central Oregon has been severe enough to result in extensive stand loss in absence of larval control. It is more a problem in sandier, non-compacted soils.
Biology and life history Beginning in mid-April, larvae hatch from eggs laid by moths the previous summer. Larvae feed through June, pupate, and emerge as moths in late June and early July. Moths are active during the summer and deposit the overwintering eggs on the soil beneath plants or debris through early fall. There is one generation a year.
Scouting and thresholds About mid-May, walk fields, looking closely at new growth above ground. Wilted, clipped-off shoots indicate RBC feeding. Confirm by taking soil samples to a depth of about 2 inches, screen the soil, and record numbers of larvae observed per sq ft. An average of from two to six larvae per sq ft sample can result in economic damage and oil loss (most severe in new mint and old, poor-vigor stands).
Heavier soils often escape injury from this pest. Fall plowing destroys eggs and almost always reduces larval infestations to noneconomic levels.
- acephate (Acephate 90WDG) at 1 lb ai/a. PHI 14 days. REI 24 hr. Late evening or night applications are most effective. Apply through a specified sprinkler irrigation system or with ground spray equipment in at least 10 gal/a water. Do not apply more than twice per season. OR-090026.
- chlorantraniliprole (Coragen) at 0.045 to 0.098 lb ai/a. PHI 3 days. REI 4 hr. Do not exceed 0.2 lb ai/a or 4 applications per season. Retreatment interval 14 days. May be applied by chemigation.
- chlorantraniliprole/thiamethoxam (Voliam Flexi) at 0.1 to 0.125 lb ai/a. Do not use an adjuvant. Retreatment interval 14 days. PHI is 7 days. REI 12 hr. Do not exceed 15oz/a Voliam Flexi or 0.188 lb ai/a (thiamethoxam) or 0.2 lb ai/a (chlorantraniliprole) per season. Apply in at least 10 gal water/a.
- chlorpyrifos (Lorsban Advanced) at 0.94 to 1.9 lb ai/a. REI 24 hr. Use the lower rate when larvae are less than 0.75 inch long; use the higher rate if larvae are longer than 0.75 inch. Late evening or night applications are most effective. Apply through a specified sprinkler irrigation system or with ground spray equipment in at least 10 gal water/a. One application only during growing season. Do not apply within 90 days of harvest. RESTRICTED USE IN OREGON.
- methoxyfenozide (Intrepid 2F) at 0.16 to 0.25 lb ai/a. PHI 14 days. REI 4 hr. Time applications to small larvae and egg masses. Do not apply more than 0.25 lb ai/a per application, nor more than 1.0 lb ai/a per year.