EFFECT OF CROPPING SYSTEM COMPLEXITY ON PLANT-PARASITIC NEMATODES ASSOCIATED WITH ORGANICALLY GROWN VEGETABLES IN FLORIDA
Bhan, M., R. McSorley, and C. A. Chase. 2010. Effect of cropping system complexity on plant-parasitic nematodes associated with organically grown vegetables in Florida. Nematropica 40:53-70. Two field experiments were initiated in summer 2006 in north-central Florida to compare the effects of integrating cover crops, living mulches, and intercropping on plant-parasitic nematode populations, as well as the effect of fall and spring vegetables on the multiplication rate of root-knot nematodes. Treatments consisted of seven organic cropping systems that included a summer cover crop followed by fall and spring vegetables. The summer cover crop included: pearl millet (Pennisetum glaucum), sorghum sudangrass (Sorghum bicolor x S. bicolor var. sudanense), sunn hemp (Crotalaria juncea), velvetbean (Mucuna pruriens var. pruriens), weedy fallow, mixture of pearl millet-sunn hemp, and mixture of sorghum sudangrass-velvet bean. One experiment utilized fall yellow squash (Cucurbita pepo) and spring bell pepper (Capsicum annuum) as vegetable crops, and fall broccoli (Brassica oleracea) and spring sweet corn (Zea mays) were used in the other experiment. Nematode populations were monitored at the end of the cover crop and vegetable seasons. Summer cover crops of sorghum-sudangrass or pearl millet increased root-knot nematode (Meloidogyne incognita) population levels in some instances while sunn hemp suppressed it in the broccoli-sweet corn experiment. The multiplication rate of root-knot nematodes was lowest when broccoli was planted in the cropping system. Systems with sorghum-sudangrass (alone or in mixture) increased population densities of ring (Mesocriconema spp.) and lesion (Pratylenchus spp.) nematodes, and occasionally increased stubby-root nematodes (Paratrichodorus spp.). Cover crops that increased nematode numbers when planted alone usually gave the same result when planted in mixtures with another cover crop. Other cropping systems failed to suppress plant-parasitic nematodes but maintained low densities similar to weedy fallow.