What is an Ecological Threshold in Crop Protection?

Abstract

Threshold values in crop protection should give an indication of the pest density at which control with plant protection products should be carried out or is economically reasonable. Threshold values have been developed or set for numerous arable crops over the past decades. Economic thresholds or injury levels are further terms used in these concepts. The terms can be distinguished by definition but are sometimes also used synonymously. Since the appearance and the introduction of the threshold concept in practice, it has not only been accompanied by support but also by criticism. One criticism is that changing conditions make the thresholds, once set, unusable over time. Until now, threshold concepts have been focused on yield losses and the direct costs incurred in combating them. The focus is therefore on business management. Side effects of plant protection application on non-target organisms, the food chain and other aspects of biodiversity are not considered. This is another reason for criticism of the threshold concept, since this focus means that the manifold benefits of ecosystem services are not priced, and adverse effects of chemical plant protection are not fully assessed. So far, it is completely unclear how such a damage threshold, which takes ecological facts into account, is to be derived and what data are required. Furthermore, there is a lack of initial ideas as to the magnitude of the thresholds in such a concept compared to the existing ones. Therefore, this paper deals with conceptual considerations about the basics of so-called ecological threshold concepts in agriculture and a possible approach to their development. Scenarios are discussed that represent alternative function types and courses of infestation-loss relations, taking ecological effects into account. Furthermore, it is conceivable to add effects on the cost function that have not been considered so far. The considerations lead to the thesis that such newly calculated damage thresholds should be set above the thresholds used so far, while the application practice tends to values below the thresholds known for decades. Need for action is shown.