SUSTAINABLE VEGETABLE PRODUCTION: EFFECTS OF CROPPING SYSTEMS ON WEED AND INSECT POPULATION DYNAMICS

Sustainable agriculture continues to attract the attention of policy makers, researchers, and growers. While a lot of research and extension activities have been devoted to sustainable production systems in agronomic crops, there have been few studies on vegetables. This study was conducted in 1999 and 2000 to evaluate the effect of cover crops and management systems on weed and insect populations in lettuce (Lactuca sativa). Cover crops treatments included cowpea (Vigna unguiculata), sudangrass (Sorghum bicolor), and the traditional summer dry fallow. Management systems included Conventional (CNV), Integrated (ICM), and Organic (ORG) systems. Cover crops were grown in the summer, followed by fall lettuce. Over the two years, cover crops had no effect on insect populations in lettuce, as neither cover crop is an alternate hosts for lettuce insect pests. However, the population of cabbage loopers [Trichoplusia ni (Hubner)] increased at the end of each growing season in cowpea mulch plots. The increase in loopers was greater in 2000 than in 1999. The cowpea cover crop suppressed weeds and increased yield. Lettuce yield was reduced when sudangrass was the previous crop. Soil analyses strongly suggest a possible allelopathic interaction between sudangrass residues and lettuce. The ICM system reduced production inputs. For example, the number of insecticide applications was reduced from four to one without an increase in insect damage. After two years, the ORG system produced lettuce yield equivalent to that obtained in the CNV system. Cowpea cover crop offers many advantages in vegetable based cropping systems. Cowpea and sudangrass are compatible with CNV, ICM, and ORG management systems.