A new study suggests a common weed killer may be linked to the mysterious global rise of young colorectal cancer . The first-of-its kind study published Tuesday in the journal Nature Medicine, suggests that picloram — a herbicide used globally to kill woody plants and shrubs while keeping grasses intact — could explain the rising incidence of colon and rectal cancer cases in people under 50. Picloram did not appear to be significantly linked to cases of colorectal cancer in adults over 70 years