Effects of combinations of host genetic variability, nematicides, rainfall and species interactions on nematode community associated with lima beans

Post-plant treatments with carbofuran and aldicarb at 2.5 kg a.i./ha significantly increased seed yields of lima bean cv. Davis White, but miral and oxamyl treatments were not significantly different from control. Nematicidal efficacy on concomitant populations of Helicotylenchus microcephalus, Meloidogyne javanica and Pratylenchus selaensis, likewise species interactions and response to rainfall, differed 011 cv. Taiwan Ace. 1066 to cv. Davis White, respectively susceptible and resistant to M. javanica. Miral and aldicarb were in order most effective in the control of H. microcephalus and M. javanica on either cultivars. Against P. selaensis, miral and oxamyl gave the best control on Taiwan Ace. 10.6 and Davis White, respectively. A cultivar resistance varied with species within a field nematode community, though resistant to two contemporary species, it positively reacted to another. Miral and aldicarb caused alterations in species interactions of H. microcephalus, M. javanica and P. sefaensis, but carbofuran was passive. H. microcephalus was more influenced by rainfall than M. javanica on P. selaensis. Treatment with nematicides increased/decreased nematode response to rainfall depending upon either nematicide or cultivar used. Nematode community structure was imbalanced in relation to interactions of the cultivar genetic variability, nematicide selectivity, competing species and rainfall to the advantage/disadvantage of a nematode species in a given field situation. This is believed to be the first report of H. microcephalus on lima beans.