Author : Pamorntip Aksorntong

Summary : Among the susceptible crops grown in farmers' fields, R. reniformis and M. incognita populations were relatively low and changed only slightly during the first six (for the former) or eight (for the latter) weeks of cropping, then drastically increased 2 weeks later until they peaked on the 12th week. After the peak periods, populations steadily declined until the 16th week, then regardless of whether or not the crops were already finally harvested, rose up again on the 18th week. Except for the differences in nematode densities and peak periods, a similar trend in population changes of nematodes occurred in the resistant crops. It appeared that the population changes on the nematodes were related with root growth, nematode reproduction, and food supply. Rainfall influence on nematode populations at the ends of the cropping periods or even two to four weeks later was indicated. Planting-site application of carbofuran 3 G at the rate of 1.125 g/hill numerically suppressed the R. reniformis and M. incognita populations on the nematode-susceptible tomato, cowpea, and squash and on the resistant sweet pepper and watermelon starting from 2 weeks after application until the 18th week or 0 to 4 weeks after the termination of the cropping periods. However, the suppressive effect of the chemical was not enough to increase the crop yields. This precluded our determination of the effect of changes in nematode population on crop yields. Hence, a higher rate of carbofuran should be applied in order to determine this effect.