Populations of Pratylenchus penetrans in plots treated with a 92% solution of 1,3-dichloropropene (1,3-D) at 47, 70, 94, 117, or 140 L/ha of formulated material increased less than in control plots when this fumigant was injected under an untilled winter cover crop with a sweep-shank injector. Linear regressions of posttreatment P. penetrans populations or population changes against 1,3-D rates were significant (P .ltoreq. 0.01) at one of two locations. Fumigation at 140 but not 94 L/ha resulted in contamination of groundwater by cis and trans 1,3-dichloropropane within 68 days of application. Water samples taken 83 days after fumigation also contained 1,2-dichloropropane. Peak concentrations of these chlorinated hydrocarbons in groundwater occurred 83 days after fumigation. Abnormally heavy rainfall (11 cm) that occurred within 6 days of fumigant application probaby reduced fumigant efficacy and enhanced pesticide leaching. The need for research to evaluate the potential for groundwater contamination by soil-applied pesticides is discussed.