Grass seed-Winter cutworm

Noctua pronuba

Pest description and crop damage Adults, commonly called large yellow underwing moths, are large (2 inch wingspan) and polymorphic, though consistently dull gray to dark reddish-brown with black markings on the upper surface of the forewing. When at rest, the hindwing (or underwing) is most distinguishable by its bright yellow to orange color with a dark band along the outer margin.

Eggs are ribbed and reticulate, and are laid in flat clusters that may be difficult to find on weed or crop foliage. They are cream in color initially, but darken to yellow as they develop. Eggs require 2 to 4 weeks to hatch, depending on conditions.

Winter cutworms are 0.125 to 2 inches in length depending on developmental stage. Coloration of larvae progresses with development, changing from greenish-gray to dark brown larvae. All larvae are characterized by dark brown/black hash marks along the sides and back, becoming more prominent toward the posterior end of the abdomen. White or cream lateral stripes run the length of the body. The light brown head capsule has a black upside-down "Y" with two black, angled lines.

The pupae are reddish-brown, about an inch long, and found hidden in cavities under the soil and debris about 2-3 inches. They are difficult to identify because of the close similarities to other Noctuid species in this pupal stage, especially armyworm and other cutworm species.

Above-ground crop damage occurs when larvae chew/notch leaves, or chew through stems completely at ground level (mowing). Root feeding has also been observed.

Biology and life history Winter cutworm was first detected in Oregon in 2001, and was recently reported in high numbers in 2015, feeding on many crops including grass seed fields, cover crops, grass pastures, lawns, meadows, sod, golf course collars, the approach to putting greens, foliage of vegetables, and weeds. Periodic outbreaks have occurred, though the environmental conditions leading up to outbreaks are not well understood.

The adults are strong fliers, can migrate, and are able to disperse over long distances. Females will lay as many as 2,000 eggs over the reproductive lifespan, on both plant and non-plant surfaces, making detection difficult.

Larvae have a wide plant host range and cause a considerable amount of feeding damage to crops in a short amount of time. The caterpillars are gregarious, similar to armyworms, feeding and moving across the landscape in large groups. They are primarily night feeding, which makes detection difficult during the day. Winter cutworm is tolerant to cold temperatures, actively feeding September through March when temperatures are above freezing. Mature larvae will pupate in the early spring, while less mature larvae will continue feeding into the spring before pupating.

Sampling and thresholds Field borders should be checked regularly for the presence of larvae - search vegetation for notching, crown damage, or plants cut through the stem at the soil level. Within fields, look for low-lying irregular patches of plant damage. If damage is found, search the soil around the damaged plants to a depth of about 2-3 inches for resting larvae. Cutworms are often visible at the soil surface when present, but may burrow under leaf litter or under soil clods to rest during the day. Larvae will often curl into a characteristic C-shape when disturbed.

There are no established thresholds for winter cutworm in grass seed crops, but recommendations for armyworm management suggest thresholds of 1-2 larvae per sq ft in newly planted fields and 3-4 larvae per sq ft in mature stands. Hay and grass pastures can tolerate as many as 4-6 larvae per sq ft.

Moths are active at night and can be monitored with basic light traps.

Management - Cultural control

  • Removing border vegetation and plant residues can limit the availability of egg deposition sites and alternate food sources for larvae
  • Tilling exposes and kills overwintering and early spring pupae before planting

Management - Biological control

Populations of noctuid moths are generally kept under control by a number of natural enemies that include parasitic wasps (Trichogramma species and braconid wasps), parasitic flies in the family Tachinidae, nematodes and several bacterial and viral pathogens. Natural predators will feed on cutworms readily, including predaceous ground beetles, birds and rodents. However, the impact of these natural predators on cutworm populations in Pacific Northwest production systems is unclear.

Management - Chemical control

In general, the smallest, least mature larval stages are most susceptible to control using an insecticide. When applying, rain may help move insecticides into the soil where larvae may be resting, but too much rain will move it too deep to target cutworms. When possible, apply pesticides late in the day to increase exposure to night-feeding larvae.

  • bifenthrin (BrigadeÆ 2EC and WSB) at 0.1 lb ai/a. Apply in spring and fall when aphids are seen. Maximum amount allowed is 0.2 lb ai/a per season. Applications made no less than 14 days apart. PHI 30 days prior to harvest for forage, hay and seed.
  • chlorpyrifos (Lorsban Advanced) at 0.94 lb ai/a. For use on perennial grass seed crops only. PHI not given. REI 24 hr. Do not graze or feed hay, forage, seed, or use screenings from treated fields. Seed conditioners must be informed if seed is from a treated field. OR and ID SLNs allows up to 3 applications per year at the max rate of 0.94 lb ai/a per application. WA SLN allows 2 applications per year at the 0.94 lb ai/a rate. Washington and Idaho labels allow applications only during the year of establishment. 24c SLN WA-090010, OR-090009, ID-090003.
  • cyfluthrin (Baythroid XL) at 0.013 to 0.015 lb ai/a. Recommended on 1st and 2nd instar larvae only. PHI 0 days. REI 12 hr. Maximum amount allowed per 5 day interval is 0.022 lb ai/a. Maximum amount allowed per crop season is 0.089 lb ai/a.
  • lambda-cyhalothrin (Warrior) at 0.015 to 0.025 lb ai/a. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr.
  • lambda-cyhalothrin/chlorantraniliprole (Besiege) at 5.0 to 8.0 fl oz/acre. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr. Do not exceed a total of 27.0 fl oz of Besiege or 0.09 lb ai of lambda-cyhalothrin-containing products or 0.2 lb ai of chlorantraniliprole-containing products per acre per year.
  • spinosad (Blackhawk) at 0.025 to 0.050 lb ai/a per season. PHI 0 days graze, 3 days hay. REI 4 hr.
  • spinosad (Success or Entrust) at 0.031 to 0.062 lb ai/a. PHI 0 days forage, 3 days hay or fodder. REI 4 hr. For resistance management, do not apply Success more than three times in any 21-day period. Do not exceed 0.186 lb ai/a per season. Do not make more than six applications per season. Entrust is the formulation that appears on the OMRI list for organic production. (Supplemental label).
  • zeta-cypermethrin (Deadlock G) at 10 lb/a. Distribute granules evenly in the furrow at planting. Only one application is allowed per season. Maximum amount that can be applied is 10 lb/a per season. No rotation crops can be planted within 30 days of the last application. REI 12 hr.
  • zeta-cypermethrin (Mustang MAX) at 0.014 to 0.025 lb ai/a. PHI 0 days forage, hay; 7 days straw and seed screenings. REI 12 hr. For forage and hay use no more than 0.10 lb ai/a per season, make subsequent applications no closer than 7 days. For straw and seed screenings.