Effects of some phenylurea herbicides on photosynthesis of two wheat varieties

Photosynthesis in the shoots of winter wheat (Triticum aestivum L.) was inhibited by certain phenylurea herbicides applied via the nutrient solution. Recovery from this inhibition after short treatments was used as a measure of the rate of inactivation of these herbicides in the leaf tissue of a variety tolerant to metoxuron (Caribo) and of a less tolerant variety (Manella). The introduction of chlorine atoms into fenuron greatly reduced the rate of inactivation in both varieties, whereas that of a methyl or butoxy group had little or no effect. Metoxuron was inactivated more readily than chlortoluron and both compounds were inactivated more rapidly in Caribo than in Manella.