K.L. Heong, International Rice Research Institute, Los Baños, Philippines
A recent review by Savary et al (2012) revealed that sustainable rice pest management strategies need to be designed to fit particular pest ecology. The “one size fits all” approach appears to be unsustainable. Using a tetrahedron framework and four basic principles, the authors used selected pest examples to illustrate the concepts. The four principles were Biodiversity, Host plant resistance (HPR), Landscapes and Hierarchies. The pest tetrahedron used consists of four summits, the environment (E), the crop (C), the Pest (P) and Humans (H). The tetrahedron significantly departs from Vanderplank’s disease triangle which considered just three elements, E,C and P. The addition of humans in the framework added an important dimension to plant protection thinking.
Humans (i.e farmers) have direct effects on the Crop-Environment-Pest interactions and this is clearly illustrated by the development of secondary outbreak pests, like planthoppers, in the case of rice. There are other such examples in agriculture, like the beet army worm and leaf hoppers in cotton, the red spider mites in citrus, the mealy bugs and mites in grapes. Normally these pests occur in the crops in low numbers and they became pest problems because of insecticides being used to control other primary pest species. Similarly in the case of rice, insecticides, especially pyrethroid, are sprayed routinely or for leaf folder control in the early crop stages. Such practices make the crop more vulnerable (often more than 10 times) to later invasions for planthopper adults. Experimental and field evidence now offer clear links between farmers’ (H) practices and planthopper outbreaks, the indicator or barometer of crop mismanagement. Host plant resistance in solving this problem seems an unsustainable approach because of the pest’s strong ability to rapidly adapt to new genotypes. Realizing this the Vietnam government has issued an administrative order to curb insecticide misuse. The Thai Rice Department had banned 2 resurgence causing insecticides in June 2011.
On the other hand in the case of managing the blast disease problem, host plant resistance is central and involves all the summits in the pest tetrahedron. Efficiency and relevance of fungicide use depends on the meso – and micro climatic environment.
The tetrahedron framework can be used to provide new perspectives in considering pest problems, both current and emerging, to better focus scarce resources to tackle the right problems in the most cost effective and appropriate ways. This is particularly important as global economic, social and climatic factors reshape agricultural practices that lessen the importance of some pests while heightening the importance of others.