PEST DYNAMICS AND MANAGEMENT IN LONG-TERM ORGANIC AND CONVENTIONAL SUGARCANE PRODUCTION SYSTEMS

摘要

Pest abundance was examined in long-term experimental plots of sugarcane grown in organic and conventional systems with two sequences of plant-ratoon sugarcane separated by a rotational cotton crop. Besides, pest control measures were adopted against regular and invasive pests of main and rotation crop in the two systems. Among sugarcane pests, incidence levels of shoot borer Chilo inftiscatellus Snellen (Lepidoptera: Crambidae) recorded in 60 - 80 day old crop (2.9 - 6.8% deadhearts) tended to be lower in organic plot than in conventional plot with significant difference in only one crop. Incidence levels of internode borer Chilo sacchariphagus indicus (Kapur) (Lepidoptera: Crambidae) in 160 -280 day old crop (1.8 - 12.0% attacked canes) were generally lower in organic plot than in conventional plot in all four years with significant differences in most observations. Intensity of the borer (1.2 - 4.5%) was also generally lower in organic plot than in conventional plot with significant difference in only one crop. The invasive woolly aphid Ceratovacuna lanigera Zehntner (Homoptera: Aphididae) first appeared in ratoon-I but the low intensity did not differ between organic and conventional plots; three species of predators accompanied the aphid. In a second bout of occurrence a month later, mean aphid intensity was significantly higher in organic plot than in conventional plot; Dipha aphidivora Meyrick (Lepidoptera: Pyralidae) was the only predator noticed. Cotton planted as rotation crop harbored greater number of aphids lAphis gossypii (Homoptera: Aphididae)] per plant or leaf in organic plot than in conventional plot. In studieson management of pests, pheromone traps set up against shoot borer in both organic and conventional plots trapped large numbers of moths which, however, did not differ considerably between the plots. When woolly aphid appeared more intensely in plant-H crop than in ratoon-I crop, augmentative releases of D. aphidivora in organic plot gradually enhanced its own numbers and reduced aphid intensity. On the other hand, the aphid in conventional plot was managed by limited number of spatially restricted applications of the insecticide acephate. In ratoon-II crop, stray incidence of the aphid was naturally regulated by the introduced parasitoid Encarsiaflavoscutellum Zehnt. (Hymenoptera: Apheltnidae), which spatially and temporally restricted the aphid. The results of the study are discussed in the context of a conceptual model proposed earlier for arthropod pest management in organic crops.