In small-plot field studies, cotton yield was inversely related to initial population levels of Meloidogyne incognita. A tolerance limit of 21 juveiles and eggs/1000 g soil is estimated and maximum yield reduction was 34%. Cowpea yields, in a similar study, indicated greater tolerance to M. incognita. Yield reduction did not occur at initial opulation levels below 249 juveniles and eggs/1000 g soil and maximum reduction at high nematode densities was 12%. Nematode reproduction on cowpea in plots with low initial population levels was 6% of that on cotton. Population densities of Cyperus esculentus and Paratrichodorus minor were in direct proportion to those of M. incognita, Covariation of these organisms and Fusarium oxysporum f. sp. vasinfectum with M. incognita may allow simplification of yield forecasting methods.