Biological impact of pesticide use in different cropping patterns in Bongabon, Nueva Ecija [Philippines]

Monocrotophos treated white and red onions showed low incidence of Fusarium and Sclerotium bulb rots compared to the untreated onions. Pepper showed high disease incidence of bacterial soft rot but it had low incidence of anthracnose and stem rot while rainfed rice was heavily infested with rice rootknot nematodes and had low incidence of bacterial leaf blight. Cabbage treated with both monocrotophos and pesticide mixture was free from any disease whereas corn was infested by Helminthosporium and Curvularia leaf spots and rusts. Monocrotophos treated and untreated white and red onions had low population of insect pests. The same was true with pepper and rice, Plutella xylostella, Crocidolimia binotalis and Spodoptera sp. were present at low population levels in the monocrotophos treated cabbage, but high in the untreated. Cabbage treated with combination of Methamidophos, cypermethrin and bendiocarb had lower insect population than in monocrotophos treated plants. In corn, Spodoptera sp. had the highest population per plant followed by Ostrinia furnacalis. Application of monocrotophos and pesticide mixture resulted in low nematode population, variable effects on the air-borne fungi, and growth inhibition of soil fungi and bacteria. These soil fungi were Cephalosporium sp., other species of Aspergillus, Curvularia and unidentified species of fungi. The soil bacteria were Pseudomonas sp., all species of Bacillus and other unidentified bacterial species. Population of the rest of the species increased. Population counts of Curvularia, species of Bacillus and other unidentified bacterial species decreased when exposed to pesticide mixture. Population of the rest of the species increased. Bongabon farmers were totally dependent on chemical pesticides to control pests. They used monocrotophos and other pesticides that are not registered for the crops grown. The farmers applied pesticides on calendar bases at high dosages and unprotected by any protective gears. Pesticide residues in the treated plots exceeded the maximum residue limit set by the WHO/FAO in the atmosphere, soil, and cabbage heads but low in onion bulbs. Pesticide mixture were applied in cabbage every two days while monocrotophos was applied at 3-4 times per cropping season in onions. Re-entry and pre-harvest intervals were 3-4 hours after spraying and 2-3 days after the last insecticide application, respectively. Proper pesticide storage and disposal was not observed.