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Comparative Efficacy of Preplant Fumigation and Postplant Chemical Treatment of Replant Citrus Trees in an Orchard Infested with Tylenchulus semipenetrans

Preplant soil fumigation with methyl bromide at 49 and 98 g/m² was compared with various postplant nematicide and fungicide programs in a replant citrus orchard infested with the citrus nematode Tylenchulus semipenetrans and the fungal pathogens Phytophthora nicotianae, Fusarium solani, and F. oxysporum. Postplant treatments comprised multiple applications of fenamiphos at 4.0 g a.i./m² soil, aldicarb at 4.5 g a.i./m² soil, metalaxyl at 4 g a.i./m² soil, fose-tyl-Al stem painting at 400 g a.i./liter, and combinations of fenamiphos + fosetyl-Al and aldi-carb + fosetyl-Al at the same rates as for single treatments. P. nicotianae could not be detected in the entire experimental site after replanting, but populations of F. solani and F. oxysporum showed only a temporary decline following site preparation. T. semipenetrans did not re-establish in any of the treatments within the first 2 years. Numbers of juveniles remained low in most treatments during the third year, but thereafter both juveniles and females increased significantly in all except the fumigated plots. Female populations on roots of citrus trees planted in fumigated soil remained suppressed for 8 years and the trees developed more vigorously and produced higher yields and larger fruit than those in non-fumigated soil. Compared with the control, net income for the period 4 to 8 years after planting increased by 101 and 46% in plots fumigated with 49 and 98 g/m², respectively. With the exception of aldicarb, all other treatments showed net losses.