Abstract
In 1968 and 1969 soil samples were collected and bioassayed from 116 fields of crucifers from 14 counties in southern Ontario. Residues of T. ni viruses (nuclear-polyhedrosis (NPV) and granulosis (GV)) were found in soil from 12 counties, being detected in 68 and 45% of soil samples in the respective years. P. rapae granulosis virus (GV) occurred in soil from 7 counties, being found in 18 and 19% of samples. T. ni NPV was more common than T. ni GV. The concentration of viruses of both host species in soil was influenced by density of the host population, crop rotation, soil pH, and month of sampling.