Ecological And Economic Aspects Of Pest Management And Polycultures Of Tomatoes In Central America (heliothis, Spodoptera, Bemisia Tabaci, Liriomyza Sativae, Nicaragua).

Abstract

An analysis of economic development and agricultural ecology shows that integrated pest management (IPM) is compatible with current Nicaraguan development policy. One part of the policy emphasizes the substitution of local resources for imported inputs. As a strategy that minimizes pesticide use, IPM achieves that goal. An IPM program is presented for the pest complex on tomatoes in Nicaragua and other Central American countries. The program consists of two major components: a responsive strategy for control of the cotton whitefly, Bemisia tabaci, based on Economic Injury levels; and cultural control for other pests using polycultures of tomatoes and beans. Whitefly densities under different pesticide regimes were sampled over a season and were correlated with final tomato yields. Even low whitefly densities at 43 days after planting (DAP) caused a 35% reduction in final tomato yield. However whitefly density later in the season and yield were uncorrelated. These data suggest that farmers should discontinue the practice of spraying insecticides for whitefly control later in the season. A table of economic injury levels, for early whitefly attack, is generated for combinations of expected tomato prices and expected yields. Land Equivalent Ratios (LERS) for polycultures in Costa Rica were 1.92 and 2.41 for low and high tomato densities, respectively. In Nicaragua an LER of 1.72 was obtained, and the polyculture also overyielded economically, with a Relative Value Total between 1.09 and 2.19 depending on tomato price. In Nicaragua pest and pathogen attack was monitored during the season in 10 x 10 m plots of monocultures and polycultures. There were reductions in the polyculture of the density of the vegetable leafminer, Liriomyza sativae (P < 0.005), and of the number of fruit damaged by the tomato fruitworm complex, Heliothis spp. (P < 0.015). A similar trend was observed for the armyworm complex, Spodoptera spp. (0.05 > P < 0.10). There was no difference in levels of Fusarium, Xanthomonus vesicatoria, Phytophthora infestans, or virus. In an unreplicated large-scale test of pest suppression in the polyculture, the percent fruit damaged by the Heliothis and Spodoptera complexes was more than 10 times higher in the monoculture than in the polyculture. Another large-scale test demonstrated a trap crop effect, whereby intercropped beans protected tomatoes from Spodoptera sunia, by virtue of being the preferred host plant.