Effect of cover crop and management system on weed populations in lettuce

Changes in cropping systems can significantly impact pest population dynamics and management. Field experiments were conducted from 1998 to 2000 to study the effect of summer cover crop and in-season management system on weed infestations in lettuce (Lactuca sativa L.). The experiment was a factorial with summer cover crop and management system as the two factors. Cover crops were cowpea [Vigna unguiculata (L.) Walp.] incorporated into the soil in the fall (CWPI), cowpea used as mulch in the fall (CWPM), sudangrass (Sorghum vulgare) incorporated into the soil in the fall (SDNG), and dry fallow (DFLW). Management systems were organic (ORG), integrated crop management (ICM), and conventional (CNV). In general, there was no interaction between cover crop and management system. Weed species richness was greatest early in the growing season and was affected by cover crop. Fewer species emerged in CWPM plots in general but perennial species became important with time. The DFLW showed greater weed populations than all cover crop treatments. Weed populations were similar in all management systems in 1999. However, in 2000, there was better weed suppression in the ORG and ICM systems than in the CNV system. CWPI significantly increased lettuce yield and DFLW yield declined the second year. Yield under the ORG system was low in 1999 and equivalent to that in the CNV and ICM systems in 2000. These results indicate that a prior summer cover crops can improve both conventional and organic vegetable production systems. (C) 2002 Elsevier Science Ltd. All rights reserved.