By Nick Seiter, Extension Entomologist
Over the last few weeks, we have received several reports of adult kudzu bugs in counties where this pest has not been seen before. These insects are highly mobile at this time of year as they search for places to congregate, lay their eggs, and feed. In areas where kudzu bugs are established, it is not uncommon to find them on light colored clothing, buildings, or vehicles, especially on warm sunny days. While we have had reports of kudzu bugs in soybeans, we have not to this point had any reports of the insect at economically damaging numbers in Arkansas.
Kudzu bugs have a habit of aggregating on individual plants in high numbers, including seedling soybean. These aggregations can be alarming, as it is not uncommon for some plants to be virtually covered in kudzu bugs. More often than not, these aggregations will be limited to localized spots in the field, particularly along the field edges. In the southeastern U.S., these aggregations on seedling soybean generally occur on “early” planting dates in April and early May. Since this fits the window when much of our soybean acreage in Arkansas is planted, we expect that similar infestations of seedling soybean will become relatively common as the distribution of the kudzu bug expands in the state.
Kudzu bug infestations of seedling soybean are certainly no reason to panic. While the adults feed on plant vascular fluid, they do not appear to cause as much damage as the nymphs, which will appear later. Even at high numbers, the adults do not appear to be a threat to stand, which is our biggest concern in seedling soybean. In fact, it is not clear if these early infestations of adults result in any reductions in grain yield. Several of the southeastern states have set up a precautionary threshold of 5 adults per plant for these early season infestations. Remember, this
would be an average of 5 adults per plant across an entire field to trigger a whole-field application, an unlikely scenario given the habit of kudzu bugs to congregate around field edges. If a treatment is justified, control recommendations can be found in our MP144, “Insecticide Recommendations for Arkansas.” http://www.uaex.edu/publications/mp-144.aspx
While these early infestations can be alarming, it is during the reproductive stages of soybean that we have documented yield reductions from kudzu bugs in other states. Our threshold is 25 of the more damaging nymphs per 25 sweeps, a high threshold reflecting the large numbers that are needed to cause reductions in yield. (Remember that kudzu bugs do not directly damage the pods or seeds, and any grain yield loss is an indirect result of the stress their feeding puts on the plant). Given how new this insect is to the state, if you find it infesting soybean in numbers give us a call, as we are trying to stay on top of this insect as it becomes more prevalent in Arkansas.