Control of barnyardgrass and yellow foxtail by herbicides in relation to the sucrose content of the seedling leaves

The ability of triazine and urea herbicides to reduce the sucrose level of seedlings of barnyardgrass (Echinoehloa crusgalli (L.) (Beauv.) and yellow foxtail (Setaria Iutescens (L.) Beauv.) was compared with their effectiveness in controlling these weeds by pre-emergence application to maize. In 2 years out of 3 a significant positive correlation was obtained between the sucrose content of the third leaf and the number of these grasses on the field plots 2 months after planting. The regression of number of grasses on sucrose content for the combined treatments of 3 years was also significant indicating that, in general, control of grasses is improved as the inhibition of photosynthesis in the seedlings is increased.