Soybean Grower

Nymphs on stem
John Ruberson, University of Georgia,

Adults with dime for scale.
Jeremy Greene, Clemson University,

The kudzu bug was introduced from Asia, where it is widespread. It is the only representative of the family Plataspidae in North and South America. The insect taps through the veins of plants to reach the phloem, using piercing sucking mouthparts. As a result, injury to plants likely results from nutrient and moisture loss, rather than a direct loss of biomass from removal of plant tissue. On soybeans, the kudzu bug adults and nymphs feed on stems (last instar nymphs with purplish wing pads), while small nymphs have been observed feeding on leaf veins. In 2011, yield losses of up to 47% were recorded in Georgia on untreated beans on a research station near Midville; only two kudzu bugs were found at this location the previous fall. In North Carolina, two kudzu bugs were found at the Upper Coastal Plain Research Station near Rocky Mount in the fall of 2011.

Adult laying eggs.
Jeremy Greene, Clemson University,

Initial research indicates that the kudzu bug overwinters as adults near kudzu patches and soybean fields in plant debris and behind tree bark, but it will also attempt to overwinter in structures such as houses and other buildings, where it can be a nuisance pest.

When temperatures warm, the strong-flying adults emerge from overwintering sites and move into kudzu or wisteria where they mate, lay egg masses, and develop through 5 nymphal stages before moving into soybean as adults. In Georgia, the kudzu bug can complete development from egg to adult in 6-8 weeks. Kudzu appears to be an important initial host for the development of the first generation, and the insects have been shown to reduce kudzu biomass. Egg masses from the overwintering generation have not been observed on soybeans. Bacteria from by egg-laying females appear to provide the subsequent generation with the capability to survive on other legume hosts such as peas, beans, peanuts and the insects’ preferred host, soybean.

Yield Impact

Yield data has been collected from 19 replicated trials in Georgia and South Carolina. Yield was numerically reduced in unprotected plots in 16 of 19 trials with an average yield loss of 18 percent and a range from 0-47 percent. Kudzu bugs feed on plant sap and can be considered a stress inducing pest. Excessive kudzu bug feeding negatively impacts soybean yield by reducing pods per plant, reducing beans per pod, and/or reducing seed size. The mechanism of yield loss is likely due to the physiological timing that stress occurs on the soybean plant. These yield loss components are very similar to what we observe on soybeans which are drought stressed.

Scouting and When to Treat (Threshold)

Kudzu bugs can be scouted using a 15-inch diameter sweep net. Kudzu bug populations can be extremely high, especially on field edges. We are suggesting a threshold of one immature kudzu bug per sweep. This suggested threshold is based on 2011 field trials where a single properly timed insecticide application preserved soybean yield. In the majority of trials we have conducted, nymphs usually appear at about the R-2 to R-3 growth stage. If adult numbers are extremely high (multiple adults per sweep) and soybeans are stressed, treatment should be considered; this is a judgment call but the idea is to avoid bug induced stress on soybeans that are also stressed for some other reason. Growers should consider using Dimilin as a preventive treatment for velvetbean caterpillar since kudzu bug insecticide applications will be disrupting natural controls. This disruption may also enhance the establishment of other caterpillars such as podworms, armyworms and soybean loopers.

Insecticide Efficacy

The table below summarizes insecticide efficacy data from trials conducted in 2010 and 2011 in Georgia and South Carolina. Products which are shaded have kudzu bug on their label (2(ee) Recommendation). Several insecticides provide effective control, thorough coverage and penetration of the canopy is critical for effective control.

Efficacy Table

State and Regional Factsheets