A risk management system for controlling the foliar pests of Brassica crops

摘要

Although most vegetable growers walk their crops regularly, keep records and make decisions based on their findings, there is rarely any sound statistical basis for their various approaches. In addition, the concept of 'nil tolerance', propounded by multiple retailers, does not fit easily into a sample-based system since all plants in a field would need to be sampled to be certain that none was infested. Thus, growers require a rational and statistically sound approach to crop walking and decision-making which is in line with the quality control procedures developed and used regularly by other industries. This paper describes the preliminary results of a project to develop a robust cost-effective management system for foliar pest control in Brassicacrops. The paper focuses on the first objective of the project, which is to determine the influence of pests (principally aphids and caterpillars) on the quality of marketable crops, so that the management system can be designed to achieve an acceptablelevel of pest infestation in the end-product. Harvested crops (broccoli, Brussels sprout, cabbage, cauliflower) were sampled in packhouses to determine levels of pest infestation prior to despatch. Losses, due to pest damage and contamination, were measured and categorised, and compared with packhouse assessments of quality. No samples was entirely free from pests. Aphids were the most numerous pest insects and high numbers of Brevicoryne brassicae (cabbage aphid) and Myzus persicae (peach-potato aphid) were found at several sites. Caterpillars were considerably less numerous. Slugs and slug damage were also evident at several sites and, at one location, slugs had damaged 295 of 300 cabbage heads.