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Biological Impact of Pesticide Use in Different Cropping Patterns in Bongabon, Nueva Ecija
Dissertation Abstract:
A one-year study which investigated five specific areas regarding pesticide use in Bongagon, Nueva Ecija, Philippines was conducted. The specific areas investigated inlcuded the: 1) existing species and population of different plant pathogens and insect pests; 2) abundance and succession of insect pests and diseases on different growth stages of crops; 3) disease incidence and population of pathogens on different cropping patterns after pesticide treatments: 4) pesticide residue in soil, air, and plants as a consequence of pesticide application; and 5) pesticide management practices employed by the farmers.
In white onion-pepper, red onion-rice, cabbage-com, and red onion-corn cropping patterns, white and red onions were attacked by Fusarium and Sclerotium bulb rots; pepper by bacterial soft rot and anthracnose; rice by rice root knot and bacterial leaf blight; and corn by Helminthosporium leaf spot, Curvularia leaf blight, and leaf rust diseases, Cabbage, on the other hand, remained disease-free.
White and red onions were infested by Spodoptra sp. and Liriomyza sp. Bemicia tabaci, Aphis gossypu and Nirvana sp: rice by Tryporyza incertulas, Leptocorisa aratoria, Nephotetlix sp., Oxya sp., and Cnaphalocrosis medinalis; cabbage by Plutella xylostella, Crocidolomia binotalis, Spodoptera litura, and five minor insect pests; and corn by Ostrinia furnacalis and other insect pests of min or importance.
Monocrotophos-treated white and red onions showed low incidence of Fusarium and Selerotium rots compared to the untreated onions. Pepper showed high disease incidence of bacterial soft rot but had low incidence of anthracnose and stem rot. Rain fed rice was heavily infested with rice root knot nematodes and had low incidence of bacterial leaf blight. Cabbage treated with both monocrotophos and pesticide mixture remained disease-free, while corn was infected by Helmithosporium 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. P. xylostella, C. binotallis, and Spodoptera sp. were present at low population level in the monocrotophos-treated cabbage, but high in the untreated. Cabbage treated with a 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 O.furnacalis.
Application of monocrotophos and pesticide mixture resulted in low nematode population, variable effects on the airborne fungi, and growth inhibition of soil fungi and bacteria. These soil fungi were Cephalosporium sp., other species of Aspergillus, Curvularia, and an unidentified species of fungi. The soil bacteria were Pseudomonas sp., all Bacillus species, and other unidentified bacterial species. The population of the rest of the species increased. Population counts of Curvularia, Bacillus species, and other unidentified bacterial species decreased when exposed to pesticide mixture while the population of the other species increased.
Bongabon farmers totally depended on chemical pesticides to control pests, using monocrotophos and other pesticides that were not registered for the crops grown. The farmers applied pesticides on calendar basis at high dosages and unprotected by any protective gears. Pesticide residues in the treated plots exceeded the maximum residue limit set by the World Health Organization/United Nations Food and Agriculture Organization (WHO/FAO) in the atmosphere, soil, and cabbage heads but low in onion bulbs.
Pesticide mixtures were applied in cabbage every two days while monocrotophos was applied 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, with empty pesticide bottles sold in junk shops or left in the field. Sprayers were washed in irrigation canals or creeks.
Pesticide poisoning was generally suicidal in nature and others were occupational and accidental. Cases involved were mostly male farmers who were 11-20 years old. The usual pesticide poisoning symptoms identified by respondents were dizziness, headache, nausea, chest pain, salivation, and difficulty in breathing.