Influence of Aldicarb and Fenamiphos on Tylenchulus semipenetrans Population Densities and Orange Yield

The effect of aldicarb and fenamiphos on Tylenchulus semipenetrans population densities and on orange yield was investigated during a 3-year (1986-88) field trial in Italy. Rates were 10 and 20 kg a.i./ha as an early spring single application, 5 kg a.i./ha in spring and 5 kg after flowering, and 5 kg a.i. in spring followed by 2.5 kg/ha after flowering and 2.5 kg/ha in early autumn. Rates and times of application of the two nematicides did not affect numbers of females of T. semipenetrans on the roots but suppressed (P = 0.05) egg, male, and second-stage juvenile population densities from October 1986 to 1988. Yield of fruit was not affected by any treatment during 1986-87. Yield was increased (P = 0.05) in 1988 by i) a single application of 20 kg a.i./ha aldicarb, ii) 10 kg a.i./ha fenamiphos, and iii) an application of 5 kg a.i. aldicarb/ha in spring, followed by two more applications of 2.5 kg/ha each in June and September. Fruit size was not affected by the nematicide treatments. Concentrations of fenamiphos and its metabolites, in rind and pulp, were below 0.02 ppm.