BEET ARMYWORM: Spodoptera exigua, Noctuidae

ADULT: Fore wings are brownish-gray with fine light and dark markings. Round spot in middle of wing (orbicular spot) is cream colored or with orange center. Hind wings are light colored with a dark band near margin. With a wing span of 1 1/4 in., they are smaller than the fall armyworm adult.

EGG: Moths produce a mass of up to 100 eggs covered with scales. Larvae emerge in 3 to 4 d.

LARVA: Newly emerged larvae are light with a dark head. As they mature over the 2 wk. larval stage, they become light to dark green with a light and dark stripe above the spiracles and another light stripe below the spiracles running the length of the caterpillar. There is usually a dark spot above these lines on the second thoracic segment.  Sutures on front of head form an inverted "Y". Larvae have three pairs of true legs and five pairs of prolegs.

PUPA: Dark brown pupae are found in soil. Adults emerge from pupal cases in 7 to 10 d.

GENERATION TIME: 25 to 28 d.

DAMAGE: Although an infrequent pest on corn, beet armyworm can damage leaves and ears. Larvae feed in the whorl and at the base of expanded leaves.

CONTROL: Birds and insect natural enemies aid in armyworm control, but generally do not exert enough pressure to prevent yield loss, particularly in sweet corn. Host plant resistance is emerging as an effective control strategy against armyworms in both field and sweet corns. Varieties with insect enzyme inhibitors and new bioengineered corns with bacterial toxins will help to greatly reduce armyworm feeding pressure. Pesticidal controls are most effective against the younger instars with higher rates and more frequent applications needed to try to control later instars. Granular formulations of several pesticides are available that reduce the exposure to non-target organisms by concentrating the pesticides in the whorls and leaf axils, particularly when applied in tight bands over the rows. The other pesticides are used as broadcast or banded sprays. Fields should be monitored at least weekly until tassel push for young larvae on leaves and in whorls. Thresholds used for treatment are plant age specific, with seedlings and plants pushing tassel often treated at 10% or lower infestations. Plants between these stages are usually treated when infestations reach between 15 and 20%. Research has shown the importance of reducing armyworm populations as low as possible in the period leading up to and during tassel push. Sweet corn produces copious amounts of pollen that can compensate for damaged tassels. But it is important to eliminate the larvae being pushed from the whorl by the emerging tassel so they do not damage the sensitive emerging ears and do not pupate within the field. Armyworms completing development at tassel push will emerge as adults to lay eggs on the crop during the period of active silk growth. Fields should be scouted at least twice weekly during the ear stage to detect and control populations before they cause economic damage. Thresholds used during this period range between 2 and 8%, with estimates at the high end eliciting more frequent sampling. Formulations, rates, and pre-harvest intervals of insecticides labeled for armyworm control in Florida are listed below for sweet corn (Table 1) and field corn (Table 2).