Article by Jack Bacheler
I have been in several soybean fields during the past week in which the levels of kudzu bug adults and nymphs were many times the suggested threshold of 15 nymphs per 15 sweeps around field perimeters. In 6 of 8 cases (assessing only fields with high reported levels of kudzu bugs), sweeps taken from field interiors had sub-threshold levels of nymphs. We realize that visual observations of kudzu bug nymphs and adults may reveal many more kudzu bugs than with sweeping. However, the above presently-suggested threshold was based on sweep net sampling which is not expected to obtain all of the nymphs on a plant, but to obtain a sub-sample of nymphs that indicate a treatable population. Although possibly changing weekly in the direction more soybean fields requiring treatment, treatment has not been justified in the vast majority of our soybean fields at this point. In a number of soybean fields, the levels of kudzu bug nymphs have been lower than what we would have expected so far based on the hefty levels of adults and egg masses. This situation could change in the coming weeks. On the plus side, some early planted and/or group IV and V beans fields have reached or are approaching the R7 “kudzu bug” safe stage. Growers are again urged to observe patience with moderate to high adult levels of kudzu bugs and instead to concentrate on finding threshold levels of nymphs in field interiors. The above photo shows the pendulum sweep method in which the scout brings the sweep net down into the plant canopy. This method is more effective in detecting kudzu bug nymphs down on soybean plant stems than sweeping across the upper canopy parallel to the ground.