Defining Hierarchical Decision Trees for Encarsia Formosa Strategies from Greenhouse Tomato Consultants’ Perspectives

Market pressure is forcing New Zealand greenhouse tomato growers to shift from conventional to more environmentally-friendly pest control methods such as IPM (Integrated Pest Management). Growers can access IPM manuals, but these tend to provide generalized advice, which they find difficult to apply to their own situations. Alternatively, growers can use consultants to tailor IPM strategies to their own situations. One method of providing growers with better advice is to capture the knowledge of “expert” consultants and translate this into a form that can be used by growers. To this end, two consultants with expertise in IPM strategy were studied and their knowledge documented. This paper focuses on the strategies the expert consultants used to tailor Encarsia formosa, a natural enemy of greenhouse whitefly, to individual greenhouse’s specific needs. Both consultants used an IPM template and seven to eight decision criteria to tailor their advice to individual grower’s situations. These decisions were represented as hierarchical decision trees. One consultant started with low Encarsia rates for a short time before increasing them while the other consultant started with high Encarsia rates for a longer period before decreasing them later. Growers’ risk perceptions and acceptance of the consultants’ pest threshold levels influenced the success of the IPM strategy.