Pest control and soil management in the Guatemalan highlands: Understanding traditional agricultural practices.

Abstract

Extension of integrated pest management (IPM) technology in recently introduced vegetable export crops in the Guatemalan highlands has been largely unsuccessful. Efforts to overcome the failure of the IPM diffusion-adoption process have been ineffective, in part because farmers are not generally taken into account in the research process. Understanding farmers' agricultural knowledge must be an early step in research. I conducted a semi-structured survey of 75 Cakchiquel Maya farmers in Patzun, Guatemala, to begin documenting their pest control practices. Their knowledge of biological and curative pest control is limited. Nevertheless, their broad knowledge of preventive agronomic pest control practices explains why they had few pest problems in their milpas (traditional intercrops of corn, beans, and other edible plants). According to agroecological theory, the majority of these preventive practices are efficient and environmentally innocuous. However, scientists know little about the pest control practice that farmers mentioned most: application of organic fertilizers. I conducted a series of experiments to test the impact of fertilizers on corn pests. Field trials compared effects of organic and synthetic fertilizers on herbivorous insects and their natural enemies. Corn plants treated with traditional organic fertilizer applied for at least two years hosted fewer aphids (9.14 aphids/plant), than those treated with synthetic fertilizer (19.18 aphids/plant). Complimentary bioassays in an olfactometer and with corn growing in screened boxes, revealed that aphids are attracted to plants treated with synthetic fertilizers 3.42 times as frequently as to those grown with manure. Aphid reproductive rates on the synthetically fertilized corn were 1.07 times those on the organically treated plants. Foliar nitrogen concentration was higher in synthetically fertilized plots (2.97%) than in the organic fertilized (2.67%), explaining in part the aphids' response. Natural enemies appear to play a role as well, as Coccinellidae populations were 3.6 times higher in organically fertilized plots. The effect of synthetic fertilizers on aphids persists for at least one year after their application. Fertilizer treatments had no effect on yields, suggesting that traditional fertilization practices in Patzun are ecologically and economically appropriate.