Bertha armyworm (Mamestra configurata)
Pest description and crop damage Several species of armyworm and cutworm attack tree fruits. The most serious pests of tree fruit in the PNW are the spotted cutworm and the bertha armyworm. Winter cutworm is a relatively new cold-tolerant species that may at times occur in orchards (see: EM9139, https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pd...). The adults are large moths ranging in color from gray to brown with spots on the wings. These moths are attracted to lights. Larvae are dirty white, reddish, gray or black caterpillars up to 2 inches long. The larvae of these moths feed on buds and leaves, chewing holes in buds and ragged holes out of leaves. They also feed on the growing tips, particularly on small trees or in high density plantings. On larger trees, most of the feeding is on the lower branches, and may be concentrated to a few stems or limbs, while other stems are undamaged.
Biology and life history Weeds are the preferred source of food for these larvae, and eggs typically are laid on weeds around the trees. Depending on species, they may overwinter as pupae or larvae in the soil. The larvae spend the day in the soil, then climb up the tree during the night to feed, often following the same path.
Control weeds, grasses, and debris in the orchard that provide cover. Natural enemies of cutworm include birds and spiders. Hand-pick cutworm larvae, using a flashlight to find them, if practical. Scratch the soil at the base of plants to find larvae in the daytime. Caterpillars can be trapped by tying plastic wrap tightly around branches and trunk, then applying Tanglefoot or a similar sticky material to the plastic wrap. Remove these in the fall.
Management-chemical control: HOME USE
Spring and summer
- azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
- Beauveria bassiana-Some formulations are OMRI-listed for organic use.
- insecticidal soap-Some formulations OMRI-listed for organic use.
- kaolin clay-Applied as a spray to leaves, stems, and fruit, it acts as a repellant to target pests. Some formulations are OMRI-listed for organic use.
- pyrethrins-Some formulations are OMRI-listed for organic use.
- spinosad-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
Spring and summer
- acetamiprid (Assail 70WP) at 3.4 oz/a in up to 100 gal water per application. Do not make more than 4 applications per year or exceed 13.5 oz/a per growing season. REI 12 hr. PHI 7 days. [Group 4A]
- Bacillus thuringiensis (Dipel DF, Javelin, etc.)-Formulations vary; see label for rates. Apply Bt materials two to three times, beginning at prepink, repeating at pink and petal fall. Apply Bt only when temperature exceeds 60°F. REI 4 hr. PHI 4 hrs. Some formulations are OMRI-listed for organic use. [Group 11] [larvicide]
- chlorantraniliprole (Altacor) at 3.0 to 4.5 oz/a in no less than 100 gal water per application. Do not apply more than 9 oz/a per growing season. Do not use an adjuvant within 60 days of harvest. REI 4 hr. PHI 5 days. [Group 28]
- phosmet (Imidan 70W) at 2.1 to 5.7 lb/a in up to 100 gal water per application. REI/PHI 7 days. [Group 1B]
- spinetoram (Delegate WG) at 4.5 to 7 oz/a in up to 100 gal water per application. Do not exceed four applications or 28 oz/a per growing season. PHI 7 days. [Group 5]