Two citrus orchards, identified in 1982 as having patches of trees infected by Tylenchulus semipenetrans, were used to study the long-term effect of the nematode on tree quality. In 1992-93, the distribution of infected trees in both orchards continued to be aggregated. Trees were selected in one of the orchards, which had only trace amounts (0-17 juveniles and males/100 cm soil), or high levels (500-9 875 juveniles and males/100 cm soil) of the nematode. Six edaphic and biotic variables measured in soil from the two groups of trees were not different (P 0.05). Percent silt was slightly higher (3.0 vs. 1.4%) in soil with trace numbers of nematodes. There were no differences between the two groups of trees in variables that reflect long-term damage (tree height, canopy diam, and canopy density). However, fibrous root mass density, leaf area, and fruit yield were 33, 8, and 23% lower, respectively, on trees heavily infected by the nematode.
