The economic threshold is a key IPM decision-making tool. Thresholds are based on considerable amounts of research and/or field experience. If the economic threshold is approached, but not reached, do not apply a pesticide at that time. Instead, re-scout the field within a few days to determine the status of the infestation. Pest populations can decline naturally due to mortality from natural enemies and unfavorable weather conditions. Also, many pests, such as caterpillars, change from an active feeding (larva) to a non-feeding stage (pupa) during their development. Such changes will often produce a natural decline in infestations as pupation occurs.
Why Aren’t There ETs Available for Every Pest?
ETs are notoriously difficult to determine. At first glance, an ET would appear to be a straightforward, cost-benefit relationship involving control costs and market values. However, if you consider the influence of multiple pests on a crop , injury per individual pest, crop response to injury at various stages of development, varying climactic conditions, nutritional stresses, varietal differences, the purpose for which the crop is grown and fluctuating market values, then you can see how ETs might be slow in development and constantly changing.
Who Needs ETs?
We all do! ETs are the most effective method of determining if control is justified. Also, if pesticides are to be used, ETs help determine timing of pesticide applications. ETs are available that work quite well in maximizing the effectiveness and minimizing the number of spray applications for many pests. Some are still under development and many more need to be
developed. ETs represent a giant step forward in timing pesticide applications when compared to calendar or preventive spray schedules.