Summary:In glasshouse experiments 1,8‐naphthalic anhydride (NA) and N,N‐diallyl‐2,2‐dichloroacctamide (R 25788) were investigated in combination with perfluidone for the control of Rottboellia exaltata Linn. F. in maize. Both protectants were used as seed dressings and R 25788 also as a spray mixture with the herbicide.Surface application of the herbicide generally resulted in greater crop damage than incorporation. The protectants caused no damage than used alone. Both compounds greatly reduced crop damage from perfluidone treatments. In most experiments protection with NA was better and more reliable than with R 25788. Even when kept until flowering no adverse effect at later stages of growth were noted.Good control of R. exaltata was achieved in all trials where perfluidone was applied to the soil surface. Incorporation reduced activity. Mixtures of R 25788 with the herbicide did not significantly protect the weed.Field treatments to improve the tolerance of maize to perfluidone while controlling a wide range of weeds arc su