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 (Stern et al. 1959). 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.
Stern, V.M., R.F. Smith, R. van den Bosch, and K.S. Hagen. 1959. The integrated control concept. Hilgardia. 29: 81-99.