Preplant bed fumigation of lettuce soils significantly increased lettuce head weights in three Palo Verde field trials with DD and Telone. Treatments also produced trends toward more uniform and earlier crop maturity (although differences were not statistically significant). The reasons for the beneficial responses are not completely understood, but the responses were at least partly accounted for by the control of two nematodes, Tylenchorhynchus clarus and Meloidognye hapla.

Cooperators in these trials included Fred Briggs and Bill Johnson of the Wilco Produce Co., and Robert R. Mecilizo of John Norton Farms.