Thresholds are a critical part of any integrated pest management (IPM) program. The thresholds presented here are economic thresholds (ET), in which the density of a pest has reached a point at which a management intervention (in this case a pesticide application) is economically justified. An economic threshold should not be confused with the economic injury level (EIL). An economic injury level is the lowest population density of a pest that will cause economic damage. Treatment when economic injury level is reached may result in the highest yields, but may not necessarily be the most cost-effective. Treatment at the economic threshold is the most cost-effective management approach, and may or may not result in the highest yields.
For specific information, please consult the individual pest pages for various management strategies, tactics and applicable threshold information. Below you will find information on corn earworm (soybean podworm) and stink bug thresholds in soybeans.
Applying thresholds: When scouting, some level of insects and their damage will always be observed. However, most situations will not result in yield loss since the insect numbers present are too low to produce injury beyond the plant’s compensation ability. Thresholds are levels of pest injury or insect numbers (that are assumed to cause injury) that will result in yield loss beyond the cost of a remedial action (usually spraying with an insecticide). Current thresholds for soybean insect pests in North Carolina are:
Defoliation threshold (any insect or group of insects) — 30% foliage loss up to two weeks prior to blooming or 15% foliage loss from two weeks prior to flowering and until pods have filled.
Kudzu bug thresholds: Our threshold for spraying is five bugs per plant until mid-July, when we switch to a sweep net-based threshold. Remember that when you spray colonizers during the early season (the adults) you may have to spray again and again. Our best kudzu bug insecticides have little to no residual to control the insect. Once the migration period is over, they can easily be managed with a single spray since they are not difficult to kill.
After mid-July, kudzu bug is more effectively sampled with a sweep net. Several randomly selected samples of 15 sweeps (defined, firm pendulum “swooshes” of the net) per sample should be taken from interior areas of the field. A preliminary threshold of one nymph-stage bug per sweep (i.e.,15 nymphs per 15-sweep sample) is recommended and may help reduce the need for multiple sprays.