Suspected glyphosate-resistant Amaranthus palmeri plants were collected from 23 locations of the San Joaquin Valley.

They did not survive the label rate of glyphosate at the 4 to 6 leaf growth stage.

However, when they were sprayed at later growth stages several plants survived the label rate of glyphosate.

Therefore, escapes of A. palmeri in these locations may be due to glyphosate applications at later growth stages.

Several alternative herbicides and herbicide combinations were identified for the control of A. palmeri populations.