REDBACKED CUTWORM LIFE CYCLE AND HABITS

Redbacked cutworm, Euxoa ochrogaster, and a complex of other Euxoa species (E. olivia, E. messoria, E. infracta, E. septentrionalis, and E. recula) feed on mint and other crops east of the Cascade Mountains. These other cutworm species occur at about the same time as the redbacked cutworm but they have different life cycles and the larval feeding damage overlaps among the different species from March through June.

Redbacked cutworm overwinters in the soil either as eggs or larvae. Eggs hatch in March and April as soil temperatures increase. Larvae feed on mint roots beneath the soil surface by day and/or on foliage during the night. Individual larvae feed for 5 to 8 weeks. Most of the damage occurs in late April, May and early June. When mature, the larvae pupate in earthen cells in the soil.

Adults begin emerging in July and flight continues until late August or early September (Berry, 1975). Moths are active at night. Females deposit eggs during late August and early September. Embryonic development occurs immediately. However, eggs of this species do not hatch until the following spring. There is only one generation each year.

MANAGEMENT AND CONTROL OF REDBACKED CUTWORM

Redbacked cutworm, black cutworm and other Euxoa species are pest on mint east of the Cascade Mountains. These cutworms are most common east of the Cascade Mountains. Soil samples should be taken from mid-April through June (Danielson, 1976, Danielson and Berry, 1978). Wilted plants cut off at the soil surface and slow-growing mint in the spring may indicate the presence of cutworms. The larvae can be seen on the foliage or the soil surface on warm nights with a flashlight. Square foot soil samples to a depth of 2 to 3 inches should be taken in mint fields from early April to mid-June to determine if this cutworm is present and numerous enough to warrant chemical control. At least one soil sample should be taken for every 1 to 2 acres with a minimum of 25 samples per field. The treatment threshold depends on the age and vigor of the field. See Shields and Berry (1980), Soil Samples for Redbacked Cutworm in Peppermint, EC 1009, for detailed information on the construction of sampling equipment, its use, treatment thresholds, and sequential sampling for redbacked cutworms in differently aged fields.

Sequential sampling plans have been developed for redbacked cutworm in differently aged fields (Danielson 1976; Danielson and Berry, 1978). For established fields, treatment is recommended if an average of 7.0 larvae/1000 cm2 are found in 25 samples taken from different sites in the field. Treatment is not recommended if the average number of larvae per sample is less than 3.0/1000 cm2. In newly planted fields, treatment is recommended if an average of 1.5 larvae/1000 cm2 are found in 25 samples taken from different sites. If the average number of larvae per sample is less than 0.5/1000 cm2, no treatment is necessary. Vigorously growing plants can withstand more cutworm injury than plants growing under stress. In addition, fields greater than 6 to 8 years old that have other pests such as weeds, nematodes, or diseases are likely to be more susceptible to cutworm injury.

Natural parasites occur in mint fields in central Oregon and have been shown to decrease the populations of Euxoa sp. by as much as 80 per cent. The principal parasites in areas east of the Cascade Mountains are Porizintinae species and Copidosoma sp.

If treatment is justified, refer to the insecticide table for a list of insecticides and rates that are registered for use on mint to control redbacked cutworm. If you use Dyfonate apply it at least 3 weeks prior to Sinbar (terbacil) and longer if new mint, poor vigor, or on sandy soil. Lightly incorporate granules and irrigate to seal soil surface. Lorsban and Orthene also are registered against redbacked cutworm. Lorsban is most effective when lightly incorporated and irrigated in immediately after application.