Cell Membrane Disruptors

There are two groups of herbicides which are commonly referred to as cell membrane disruptors: the Photosystem 1 (PS1) electron diverters and the PPO inhibitors. Diquat and paraquat are the only current members of the PS1 group and are foliar applied, non-translocated, non-selective herbicides. Paraquat is also used as a crop desiccant. When diquat and paraquat molecules enter cells in leaves, they pick up electrons from photosynthetic processes and cause reactive compounds to be formed which rupture cell membranes.

Acifluorafen, carfentrazone, flumioxazin, fomesafen, oxyfluorfen, saflufenacil and sulfentrazone are examples of PPO inhibitor herbicides. Most PPO inhibitor herbicides are post-emergence herbicides but some (flumioxazin, oxyfluorfen and sulfentrazone) have both post emergence and pre-emergence activity. During photosynthesis PPO inhibitors, prevent protoporphorinogen oxidase (PPO) from producing protoporphorin, reactive compounds form and cell membranes rupture.

On plants affected by these herbicides symptoms include a water soaked appearance to foliage (+/- wilting) followed by dessication (browning) of tissue. Light is needed for activity and symptoms develop quickly on bright, warm days. With both groups of herbicides, best post-emergence control is achieved when applied to small weeds.

Photographs by Dr. Michael Pfeiffer

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