Control of citrus nematode Tylenchulus semipenetrans on fine-textured soil with DBCP and oxamyl

Three grapefruit orchards on sour orange rootstock were treated by metering DBCP (l,2-dibromo-3-chloropropane) at 56 kg(a.i.)/ha into 15 cm of water in a flood irrigation system. In orchards with 43-49% clay in the surface foot, DBCP reduced numbers of Tylenchulus semipenetrans below control levels for 1.5-2.0 years. In the 3 orchards, DBCP treatment resulted in increases in yield or fruit size in the 2 seasons following treatment. No increases in yield, fruit size, or fruit numbers were observed the third season after treatment, but retreatment of a portion of one orchard after 2 years resulted in large increases in yield and fruit numbers the following harvest. Application of oxamyl twice annually as a foliar spray at 2.8 kg(a.i.)/ha reduced nematode populations to about 50% of control levels and resuhed in a large increase in yield in 1 of the 2 seasons tested. DBCP treatment of fine-textured soils controlled citrus nematode and increased yields, but its effect was not as long lasting as on coarser soil in other citrus areas. Foliar applications of oxamyl reduced nematode populations but were not as consistently effective as DBCP treatments.