Cell Membrane Disrupters

The cell membrane disrupters include the diphenylether and bipyridylium herbicide families. These herbicides are postemer-gence contact herbicides that are activated by exposure to sunlight to form oxygen compounds such as hydrogen peroxide. These oxygen compounds destroy plant tissue by rupturing plant cell membranes. Destruction of cell membranes results in a rapid browning (necrosis) of plant tissue. On a bright and sunny day, herbicide injury symptoms can occur in one to two hours. Because these are contact herbicides, they are excellent for burn down of existing foliage and postemergence control of annual weeds. Perennial weeds usually regrow because the herbicides do not move to underground root or shoot systems. These herbicides have little phytotoxicity through the soil.

1. Bipyridyliums

a. Use: Paraquat (Gramoxone Extra) for non-selective weed control in corn, soybean, dry bean, sunflower, sugarbeet, small grains and dormant alfalfa and for desiccation of potato and sunflower.
Difenzoquat (Avenge) for barley, winter wheat and some spring and durum wheat varieties.

b. Injury Symptoms: Drift on sugarbeet often will appear as spotting of leaf tissue (Photo 36). High amounts of drift or an accidental application may cause patches of brown tissue on leaves (Photo 37). Spots from bipyridylium drift (Photo 38) have been confused with foliar diseases such as Cercospora or bacterial blight. Generally the pattern of injury in a field can be used to distinguish between disease and drift. If in doubt, samples should be taken to a diagnostic laboratory for disease identification.

c. Site of Action: Activated by photosystem I (PSI).

2. Diphenylethers

a: Use: Acifluorfen (Blazer) for soybean.
Lactofen (Cobra) for soybean.
Fomesafen (Reflex) for soybean.

b. Injury Symptoms: Affected leaves will exhibit dessication where the herbicide contacted the plant (Photo 39). Drift gen-erally will not kill sugarbeet but the plants may be severely stunted. New leaf growth will appear normal.

c. Site of Action: Inhibition of photoporphyrinogen oxidase (Protox).