The lower Yakima Valley of Washington is a highly diversified irrigated agricultural region bordered by dryland wheat fields. Residues of herbicides sprayed in wheat can be atmospherically transported to susceptible nontarget crops in the valley. Nontarget crops may be exposed repeatedly to low levels of herbicide residues. The effects on grapes exposed to phenoxyacetate herbicide drift has been well documented, but the effects of comparatively newer wheat herbicides like sulfonylureas (SUs) are less known. Potential effects of repeated exposures of grapes to an SU herbicide were assessed in a simulated drift study. Grape vines of the cultivar “Lemberger”; were sprayed up to three times at a weekly interval with 1/100 (0.01X) of a field application rate of chlorsulfuron, which is a postemergence wheat herbicide. Thirty‐five days after the first application, photosynthesis and stomatal resistance of randomly tagged, fully expanded leaves were measured. Total leaf area and chlorotic leaf area were also measured on the same leaves. The percentage of chlorotic area was calculated to determine the correlation between chlorotic area and photosynthetic activity of the leaf. Foliar injury was indexed on a numerical scale and scored in three intervals over 120 days of growth.