Corn earworm (Helicoverpa zea)
False corn earworm (Heliothis phloxiphaga)
Bertha armyworm (Mamestra configurata)
Tobacco budworm (Heliothis virescens)
Spotted cutworm (Xestra c-nigrum)
Alfalfa looper (Autographa californica)
Cabbage looper (Trichoplusia ni)
Pest description and crop damage Several moth caterpillar species (Order: Lepidoptera; Family: Noctuidae) can be found in hemp in the PNW. All these caterpillars or larvae have three pair of true legs behind their head. The corn earworm, tobacco budworm, bertha armyworm, and spotted cutworm are varied in color, but all have five pair of pro-legs towards the rear end, while the larvae of both looper species appear as green caterpillars with white longitudinal stripes and have just three pair of pro-legs at the rear end. Loopers move in a looping fashion, like an inchworm.
The corn earworm is the most damaging of these caterpillars as it feeds on the floral parts (mainly flower buds) of hemp plants. Also, corn earworm caterpillars sometimes nestle within flower bud materials, making it harder to scout for them on plants. Corn earworm feeding on flower buds creates extensive bud tunneling and wounds, allowing pathogens to invade that can aid development and presence of bud rot. Loopers chew holes and ragged edges in hemp leaves. Damage to mature hemp plants from caterpillars, other than corn earworm, is usually minor and does not require control. However, false corn earworm caterpillars are recently found to feed on hemp flower buds in southern Oregon, and the level of damage that this pest can cause needs further investigation.
Biology and life history Corn earworm adult moths are nocturnal. Females deposit eggs singly on hemp leaves and flower buds. Based on the available information from other crops, each female may lay up to 1,500 eggs in her lifetime, and each female may lay up to 35 eggs per day. Eggs hatch within 2 to 4 days, and newly emerged caterpillars start to feed on hemp plants, usually found feeding on flower buds. Young caterpillars (first and second instars) are small (about 2 mm in length), but they grow quickly and are fully developed (fifth and sixth instars) within 2-3 weeks. The mature caterpillars are about 25 mm in length. Corn earworm caterpillars are highly varied in color, ranging from pink, green, pale brown to almost black; however, matured caterpillars are mainly green in color when found in hemp. Mature caterpillars leave the feeding site, drop to the ground, burrow into the soil and become pupae. In summer, adults emerge in approximately 2 weeks and produce a new generation. However, in the fall/autumn, the pupae remain dormant until the following season.
Scouting and thresholds Heliothis traps baited with corn earworm pheromone lures can be used to monitor the corn earworm moth population in hemp during flowering stage. The traps should be placed at the edge of hemp fields, usually one trap per field. It is also critical to scout hemp fields for eggs and caterpillars feeding on flower buds to determine the proper treatment timing. At this point, there are no established treatment thresholds for corn earworm in hemp.
Generalist predators such as big-eyed bugs, damsel bugs and lady beetles can prey on corn earworm eggs and caterpillars. Also, corn earworm eggs can be parasitized by Trichogramma spp. and caterpillars by Archytas marmoratus and Microplitis croceipes. However, the role of these biological control agents role in controlling corn earworm on hemp has not been fully investigated.
The effect of cultural practices (such as varietal selection, crop rotation and planting date) on corn earworm management should be explored as there is currently limited information available.