Kudzu bug adults have already begun the second migration into soybeans in southern North Carolina and we anticipate this to continue for 4-6 weeks. Remember that our threshold is based on nymph catches with the sweep net (see this blog post for threshold information). Because this insect feeds on the stem, not the foliage or pods, the sweep net will capture a different proportion of insects than you are used to. Below are some tips to help you capture a representative sample of insects in the field.
- Sweep between 11AM and 3PM, when the insects are most active. Although our pod-feeding stink bugs do not move in the canopy throughout the day, the stem-feeding kudzu bug adults will move up the plant canopy and fly about during the middle of the day. Kudzu bug nymphs cannot fly and are much less mobile, but can still move around the plant. You will likely capture more insects with the sweep net during this time of the day.
Kudzu bug adults and nymphs are most often found on the main stem. Some feed on lateral stems and petioles and small nymphs may feed on the underside of leaves. Image by Alejandro Del Pozo-Valdiva.
- Our typical recommendation for a sweep net is to bury it just below the top of the canopy, sweeping all foliage in a pendulum fashion, with the top of the net even with the top of the plants. This works well for many soybean or cotton insect pests. However, because kudzu bugs are often located on the main stem, you should try to bury the sweep net deeper than normal into the canopy, brushing up against stems in the lower part of the plant.
- Bring a sharp pair of eyes with you to the field. Some of the smaller kudzu bug nymphs are round and green. At 1/10 of an inch long, these can easily get lost when you’re counting through a sweep sample. Be sure to look carefully at any that may be hiding on dislodged leaves.
- Kudzu bug is an edge colonizing species. Take at least six samples in each field and do not begin sweeping until you are at least 50 feet into the field.
Kudzu bug nymphs on the underside of a kudzu leaf. Note the color and body shape change as the nymphs grow larger. Image by Alejandro Del Pozo-Valdiva.