Correlations of field populations of nematodes with crop growth responses for determining relative involvement of species.

Treated and nontreated field plots were assayed, and the population density of each plant-parasitic nematode present was compared with crop growth and yield and with the population densities of other nematode species in the same plots. The strongest correlations between nematode population densities and growth responses occurred when soil assays for nematodes were made 55-73 days after planting. Belonolairnus longicaudatus was the most damaging parasite on peanut, Arachis hypogaea, as evidenced by high negative correlations between population densities and plant growth responses. Criconemoides ornatus, Meloidogyne hapla, Helicotylenchus dihystera, Trichodorus christie, Tylenchorhynchus claytoni, and Pratylenchus brachyurus were involved to varying degrees, depending on previous crop and initial densities of these nematodes. Hoplolaimus galeatus and Xiphinema americanum did not appear to affect crop response. The negative correlation of Trichodorus christiei to yield of soybean, Glycine max, was higher than that of Belonolairnus longicaudatus, although both contributed to yield losses. Similar correlation analyses showed that apparent antagonistic or synergistic population-density relationships among nematodes under field conditions depend on the time of sampling and the composition of the nematode community under study.