Alfalfa looper (Autographa californica)
Cabbage looper (Trichoplusia ni)
Pest description and crop damage Larvae of both species are pale green with white lines on backs and sides. Larvae have three pairs of abdominal prolegs, whereas cutworms and armyworms have five pair. Larvae of loopers move in a "looping" manner similar to inchworms. Moths are gray-brown with a silvery oval and a U-shaped spot on forewings.
In the Willamette Valley of Oregon, damage during the early season (May and early June) may appear serious. However, the plant almost always repairs the damage by harvest. This generation is usually heavily parasitized, greatly reducing potential for late-season damage from this pest.
Scouting and thresholds Inspect fields in June and early July when scouting for the more serious pests such as mint root borer, variegated cutworm, and Bertha armyworm. Count loopers the same as these pests when doing ground searches for larvae and tallying numbers for each sq ft sample. Treatment levels, which vary with vigor and age of field and the price of mint oil, usually are from one to four larvae (total of all worm species per sq ft).
Naturally occurring insect viruses are often very effective at keeping looper levels below the economic threshold. Off-color, flaccid and slow moving larvae are indicative of viral infection. Parasitic wasps and flies usually minimize summer generation damage by killing larvae in May and June. Look for small black blotches on otherwise pale green and white larvae of loopers, as these usually indicate parasitization. This insect can be controlled with Bacillus thuringiensis formulations when larvae are small and leaf coverage is complete.
Larval feeding damage in May and June, particularly in western Oregon, is usually confined to those leaves that appear in the spring on the first regrowth nodes. The great majority of these leaves will become shaded out, senesce, and fall well before harvest. Thus, treating fields with an insecticide specifically for loopers at this stage is generally uneconomical and may reduce potential for biological control by killing beneficial insects.
- acephate (Acephate 90WDG) at 1 lb/ ai/a. PHI 14 days. REI 24 hr. Do not exceed 2 lb ai/a. per season. Retreatment interval 7 days. Do not feed spent mint hay to animals. Limit 2 treatments per season.
- Bacillus thuringiensis at 0.12 to 1.5 lb/a. PHI 0 days. REI 4 hr. Treat mint when larvae are small. OMRI-listed for organic use.
- Burkholderia spp. (Venerate XC) at 1 to 4 qt/a. PHI 0 days. REI 4 hr. OMRI-listed for organic use.
- 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 adjuvants. Retreatment interval 14 days. PHI 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.
- Chromobacterium subtsugae (Grandevo) at 0.3 to 0.9 lb ai/a per 100 gal. PHI 0 days. REI 4 hr. Apply in at least 10 gal water/a. OMRI-listed for organic use.
- indoxacarb (Avaunt) at 0.065 lb ai/a. PHI 7 days. REI 12 hr. Retreatment interval 3 days. Do not exceed 0.26 lb ai/a per season. Apply in at least 20 gal water/a. May be applied by chemigation.
- 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. Retreatment interval 7 days. Do not exceed 0.25 lb ai/a per application, nor more than 1.0 lb ai/a per year.
- methomyl (Lannate SP) at 0.9 lb ai/a. PHI 14 days. REI 48 hr. Apply in at least 10 gal water/a. Do not apply more than 1.8 lb ai/a per growing season or 4 applications.
- spinetoram (Radiant SC) at 0.031 to 0.094 lb ai/a. PHI 7 days. REI 4 hr. Do not make more than 4 applications per year. Retreatment interval 4 days. Target eggs and small larvae. Do not make more than 2 successive applications of this or other group 5 insecticides (spinosad). Do not exceed 0.305 lb ai/a per season.
- spinosad (Success, Entrust SC) at 0.063 to 0.156 lb ai/a. PHI 7 days. REI 4 hr. Do not exceed 0.45 lb ai/a per crop year. Retreatment interval 4 days. Target eggs and small larvae. Do not apply more than three times per crop year. Entrust SC is OMRI-listed for organic use.
- tebufenozide (Confirm 2F) at 0.09 to 0.12 lb ai/a early season and 0.12 to 0.25 lb ai/a mid to late season. PHI 14 days. REI 4 hr. Retreatment interval 10 days. Apply in at least 8 gal water/a to small plants and 10 gal water/a to dense stands. Do not exceed 1 lb ai/a per season. Addition of a spreader-binder is recommended.
Warning: Do not use Lannate or Orthene if bees are foraging on mint or weeds during bloom. Use Confirm only in late evening if bees are present. May be applied during bloom.