Pesticide usage by farmers in Pagsanjan-Lumban catchment of Laguna de Bay, Philippines

Pesticides have been of great benefit to agriculture in the Philippines by decreasing crop losses due to insects, weeds, plant diseases, rodents, and other pests. However, they may build-up in the food chain and can cause contamination of the environment. We examined farmers’ pesticide usage in southern sub-catchments of Laguna de Bay, which is a crucial water resource subject to intensive investigations to identify types and sources of pollution. Before the monitoring of pesticides in surface waters was commenced it was necessary to conduct a survey of the pesticides being used by the growers in the catchment in order to select the pesticides that should be monitored.Our survey found that nearly all growers in Lucban and Laguna, irrespective of crop grown, used the pyrethroid-based insecticides l-cyhalothrin and cypermethrin. In rice, pesticides were applied one to three times per season, while in vegetables, l-cyhalothrin and cypermethrin insecticides were applied five times and the other insecticides were applied two to four times throughout the cropping season. In Laguna other insecticides used were carbofuran, endosulfan and a formulated product of BPMC (fenobucarb) and chlorpyrifos. In Lucban other insecticides used were malathion, profenofos, chlorpyrifos, carbaryl, niclosamide and metaldehyde. Butachlor and 2,4-D herbicides were used to control weeds and were applied once throughout the growing. Some fungicides were also applied. An estimation of the potential loads of chemicals moving into waterways has shown that l-cyhalothrin, pretilachlor, niclosamide, butalchlor, carbofuran and profenofos are most likely to be present in waterways in the Lucban and Pagsanjan regions in the largest quantities based on the quantities applied and/or use in a number of crops.

► First extensive documentation of pesticides used in this region of Philippines.
► Irrespective of crop grown, nearly all growers use lambda-cyhalothrin and cypermethrin.
► Pesticides were used more intensively in vegetable production (up to 5 applications) than in rice production (three applications).