Comparison of nematode population densities on six summer crops at seven sites in north Florida.

Densities of plant-parasitic nematodes were compared on six crops grown for forage during the summer of 1991 at seven sites in north central Florida. The cropping treatments were 'Howard' soybean (Glycine max), 'Deltapine 105' soybean, velvetbean (Mucuna deeringiana), 'California Blackeye #5' cowpea (Vigna unguiculata), 'Pioneer 3098' tropical corn (Zea mays), and 'Asgrow Chaparral' sorghum (Sorghum bicolor). Highest final densities (Pf) of Meloidogyne incognita and Criconemella spp. were obtained following corn or sorghum at most sites. The lowest Pf of M. incognita occurred after velvetbean at all seven sites, but Pf after cowpea were equivalent to Pf after velvetbean at four of seven sites. Cultivar choice is critical in planning rotations to suppress M. incognita because results obtained here and elsewhere have shown great differences among sorghum and cowpea cultivars. The Pf of Pratylenchus spp. were lowest following velvetbean at four of seven sites. There were no differences in densities of Paratrichodorus minor among crops, but populations increased at a greater rate if initial density (Pi) was low. Multiplication rates (Pf/Pi) of most nematode species on most crops varied inversely with Pi. An accurate impression of nematode multiplication and host status could not be obtained unless a range of Pi was examined.