A review of economic thresholds for invertebrate pests in UK arable crops

Abstract

The economic threshold for an invertebrate pest of an arable crop is the population density at which control measures should be implemented to prevent economic damage. It is a valuable method of determining whether or not control measures are necessary against an individual pest or group of pests. For thresholds to be effective, farmers and agronomists need to be confident that they accurately reflect the risk of economic loss in relation to the current cropping systems, as well as being practical to use. A lack of confidence can lead to the use of insurance sprays (insecticides applied irrespective of actual pest abundance), which are environmentally damaging, increase the risk of pest resistance, and decrease gross margins. We found that most current economic thresholds for pests of arable crops are not based on published evidence, and almost none account for the ability of crops to tolerate pest damage, or the amount, or type of crop damage that pests can cause. Furthermore, many of the methods of pest assessment are impractical, do not guarantee sufficiently accurate estimates of pest abundance, and are not described with sufficient detail to ensure consistency of pest assessment. Following a critique of current economic thresholds, this paper describes the relationship between invertebrate pest damage to crops, yield formation, and crop tolerance to pest damage, and describes what crop information is required to account for the capacity of crops to tolerate damage. This understanding is used to identify the key elements of economic threshold schemes for arable invertebrate pests, and describe a process by which thresholds can be applied. Finally we discuss the impact revised thresholds would have on crop production, and the further work needed to develop accurate, reliable, practical economic threshold schemes within integrated pest management strategies. We conclude that effective management of invertebrate pests in arable crops is reliant on: (1) Quantifying the crop damage a pest can cause; (2) Understanding the degree of tolerance a crop has to pest damage, and (3) Accurate and practical methods for assessing pest abundance.