SK Mathiassen et al. J Agric Food Chem (2006) Vol.54 p 1058 – 1063
“Herbicidal Effects of Soil-Incorporated Wheat”
The authors noted that wheat plants contain several chemicals with weak weed killing properties. In field trials, when wheat plants were ploughed-in after harvest, a small effect was noted on the numbers of weeds germinating and their growth in next years crops. With genetic modification, crop plants could be made to continuously exude these chemicals or to increase the dose when ploughed-in.
Control of such modification would need to be exceptionally reliable.