DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is an algicide and herbicide of the aryl urea class that inhibits photosynthesis.

In 1952, chemists at E. I. du Pont de Nemours and Company patented a series of aryl urea derivatives as herbicides.

[2][3] Subsequently, over thirty related urea analogs with the same mechanism of action reached the market worldwide.

[4] As described in the du Pont patent, the starting material is 3,4-dichloroaniline, which is treated with phosgene to form a isocyanate derivative.

In fact, it was found that DCMU not only does not inhibit the cyclic photosynthetic pathway, but, under certain circumstances, actually stimulates it.