Crop Diversification Complexity and Pest and Beneficial Organism Communities in Humid Tropical and Sub-Tropical Climatic Regimes

Non-Technical Summary: The warm, humid climate in Florida and the US Virgin Islands is both an advantage and a disadvantage for vegetable producers. The tropical/sub-tropical climate permits year-round cropping. However, lack of a winter or mild winters allow pests to persist from season to season. In addition, pest species occur that do not persist outside tropical and sub-tropical habitats. Although relatively high rainfall may reduce dependence on irrigation, year-round persistence of many pests and pathogens are encouraged. Therefore, we propose an integrated research project that will examine the effects of crop rotation, intercropping, and cover crop management on insects, weeds, nematodes, and plant pathogens in organic vegetable cropping systems. We will conduct this research under humid tropical conditions in the Virgin Islands and humid sub-tropical conditions in north-central Florida. Our research will compare crop rotation systems that include cover crops and cash crops grown in monoculture or intercropped with a control system with cash crops grown in monoculture, but without cover crops. <P> Approach: The effects of crop diversification complexity on pest populations and community dynamics will be evaluated in organic vegetable cropping systems under humid sub-tropical conditions in north central Florida and humid tropical conditions in the Virgin Islands. Mild or no winter results in the year round persistence of many pests, so alternative ways of breaking pest cycles and preventing species from achieving pest status are critically needed. Summer cover crops in monoculture or mixtures will be grown in sequence with several vegetable crops in monoculture or intercropped in a biannual rotation system. The impact of increasing plant biodiversity on growth and yield of organically produced vegetables, on the population dynamics of key insect pests and beneficial insects, weeds, plant pathogenic nematodes, and soil borne plant pathogens will be assessed. Three rotations of cover crops and vegetable cash crops designed to promote plant diversity along with a control treatment that consists of cash crops and weed fallows comprise the four cropping system treatments to be evaluated. Because the research is conducted in subtropical and tropical locations, year-round cropping is possible. Systems employing leguminous cover crops during the summer fallow will be compared with systems utilizing graminaceous cover crops and grass/legume mixtures. Legume cover crops that are well-adapted to hot, humid conditions and have been characterized as nematode suppressive, sunn hemp (Crotalaria juncea) and velvet bean (Mucuna deeringiana) will be planted at densities selected to optimize weed suppression. Graminaceous cover crops will be sorghum-sudan grass (Sorghum bicolor x S. sudanense) and pearl millet (Pennisetum glaucum). The leguminous and graminaceous cover crops in monoculture and their mixtures will be used in rotation with vegetable cash crops in monoculture or intercropped in order to promote plant diversity. Cover crops and cash crops will be evaluated for weed, insect, pathogen, nematode infestation and soil borne plant pathogens. Plant vigor, biomass, total yield and marketable yield of the cash crops will be assessed also. Biotic diversity of pest and beneficial species will be quantified through the use of species richness, species diversity, and evenness. Ordination techniques will be used to characterize how pest communities are affected by the treatments. The project is aimed at developing strategies that address pest and pest-related problems using an integrated or systems approach and at finding correlations between crop nutritional status and pest incidence. Improved control of pests in organic vegetable production will result in economic benefits to organic growers by improving marketable yields and reducing the need for labor-intensive pest management or the purchase of approved organic pesticides.