Mode of Action of the Herbicide DCMU When chloroplasts are treated with 3-(3,4- dichlorophenyl)-1,1-dimethylurea (DCMU, or diuron), a potent herbicide, O2 evolution and photophosphorylation cease. Oxygen evolution, but not photophosphorylation, can be restored by addition of an external electron acceptor, or Hill reagent. How does DCMU act as a weed killer

It acts as a weed killer by blocking photosynthesis

Explanation:

Photosynthesis is important to plants because it is their principal form of energy.

When DCMU is introduced to weeds, what it does is to block or slow down the process of photosynthesis. Carbon dioxide fixation is slowed down causing weeds to die off. DCMU strongly slows down photosystem II. When this is done, lipid and protein membranes would get destroyed and the weed cells would begin to dry and shed off