By Bob Hartzler and Mike Owen, Department of Agronomy Poison
hemlock, a biennial in the carrot family (Apiaceae), is becoming
more common in crop fields as no-till acres increase.
Infestations typically start in fencerows or other less-
intensively managed areas and creep into production fields. Like
other biennial weeds, its tolerance to control tactics increase
rapidly as the plant moves from a vegetative rosette to
reproductive stages in early spring. The simplest method of
controlling poison hemlock is to eliminate seed sources in areas
adjacent to the field. Fall applications of 2,4-D + dicamba are
highly effective against the plant. Applications to these areas
can be made following corn or soybean harvest, and infested
areas of crop fields should be treated at the same time. Poison
hemlock will not be controlled consistently by the standard
burndown program of glyphosate + 0.5 lb/A 2,4-D LVE (1 pt 4 lb
a.e./gal). Increasing the rate of 2,4-D LVE to 1 lb will improve
control, but this requires a 15 day pl