Previous studies in the field and greenhouse have shown that there are antagonistic interactions between glyphosate and chlorimuron. The basis of these negative interactions is not fully understood and is the basis for this paper. Time of application, either early morning, midday, or late afternoon were used to determine the effect of time of day on herbicide efficacy. Glyphosate provided greater control of common lambsquarters when applied in the morning than at all the other times.  There was no difference in velvetleaf control with respect to time of day. Chlorimuron had greater control of velvetleaf with the mid-day application than at other application times.

Separate subsequent applications were used to determine the ideal interval between the fast-acting and slow-acting herbicides necessary to prevent an antagonistic interaction. Applications of glyphosate followed by chlorimuron at 2, 4, 6, 8, 24, 36, and 48 hours showed no difference in weed control from the two herbicides applied initially in combination.