Kinetics of decay of candidate pesticides for integrated pest control programs

• Malaysian Agricultural Research and Development Institute, Malaysia
• National Postharvest Institute for Research and Extension, Philippines

Cooperative efforts between research and industry groups within Australia have developed and implemented integrated pest control programs that have virtually eliminated losses due to pests in bulk stored cereals in this country. However, these programs rely partly on chemical means, and little basic information is available on the behaviour of pesticides when exposed to the high ambient humidities and moisture contents that prevail in the humid tropics.
This project comprises a chemical study on the kinetics of pesticides decay during storage and processing of tropical grains, nuts and legumes. It complements ACIAR Project 8309, which will carry out the field trials of potential insecticides in Southeast Asia. In turn, scientists in the present project will not only conduct basic studies in Australia, but contribute chemical analysis expertise to the regional teams in Malaysia and the Philippines, with the dual responsibilities for monitoring pesticide residue behaviour in field trials to generate data for decay models and otherwise servicing their chemically oriented requirements.
Scientists in this project will study the insecticides approved by, or in process of approval by, the Codex Alimentarius for use on grain. These include: the organophosphorus compounds dichlorvos, malathion, fenitrothion, pirimiphos-methyl, methacrifos and chlorpyrifos-methyl; the carbamate carbaryl (and the fabric spray bendiocarb); and the pyrethroids pyrethrins, bioresmethrin, phenothrin, permethrin, cypermethrin, flurethrin, deltamethrin and fenvalerate. (The team will also investigate the effect of piperonyl butoxide on their stability of the pyrethroids). They will study the use of these chemicals in the commodities of most commercial importance in the region - paddy rice, maize, sorghum, groundnuts and soybeans - and will also include wheat, sunflower and mung beans to widen the range of grains, legumes and oil seeds.
They will carry out research on the kinetics of decay of pesticides likely to have use on tropical stored products so that, after incorporating biological data from Project 8309, they can calculate correct application rates for each commodity, having regard to type of commodity, storage period, temperature, relative humidity and processing method. (Processing will include not only dehusking and/or shelling as appropriate, but various cooking times and methods). They will unify such data, as far as possible, using models from physical chemistry. Other research will systematically investigate the ways in which oil content, protein content and 'critical moisture level' of commodities affect pesticide stability.
Specific objectives include the establishment of suitable procedures for analysis. laboratory studies will determine the effects of such factors as temperature and moisture content on the stability of various insecticides during storage, the effects of processing on that stability and, using synthesised model compounds, the relations between stability during storage and processing and such physical parameters as partition coefficients. Field trials will compare data obtained commercially with those predicted from laboratory models.
Initially the project will include cooperation with research and grain-handling authorities in Malaysia and the Philippines, but will be extended as appropriate to Indonesia.