ROLE OF NEMATODES, NEMATICIDES, AND CROP-ROTATION ON THE PRODUCTIVITYAND QUALITY OF POTATO, SWEET-POTATO, PEANUT, AND GRAIN-SORGHUM

The objective of this experiment was to determine the effects of fenam iphos 15G and short-cycle potato (PO)-sweet potato (SP) grown continuo usly and in rotation with peanut (PE)-grain sorghum (GS) on yield, cro p quality, and mixed nematode population densities of Meloidogyne aren aria, M. hapla, M. Incognita, and Mesocriconema ornatum. Greater root- gall indices and damage by M. hapla and M. incognita occurred on potat o than other crops. Most crop yields were higher and root-gall indices lower from fenamiphos-treated plots than untreated plots. The total y ield of potato in the PO-SP and PO-SP-PE-GS sequences increased from 1 983 to 1985 in plots infested with M. hapla or M. arenaria and M. inco gnita in combination and decreased in 1986 to 1987 when root-knot nema tode populations shifted to M. incognita. The total yields of sweet po tato in the PO-SP-PE-GS sequence were similar in 1983 and 1985, and de clined each year in the PO-SP sequence as a consequence of M. incognit a population density increase in the soil. Yield of peanut from soil i nfested with M. hapla increased 82% in fenamiphos-treated plots compar ed to untreated plots. Fenamiphos treatment increased yield of grain s orghum from 5% to 45% over untreated controls. The declining yields of potato and sweet potato observed with both the PO-SP and PO-SP-PE-GS sequences indicate that these crop systems should not be used longer t han 3 years in soil infested with M. incognita, M. arenaria, or M. hap la. Under these conditions, these two cropping systems promote a popul ation shift in favor of M. incognita, which is more damaging to potato and sweet potato than M. arenaria and M. hapla.