Herbicide and Nonherbicide Injury Symptoms on Spring Wheat and Barley

Cell Membrane Distruptors
In spring wheat and barley, the cell membrane disrupters include only the bipyridylium herbicide family. Herbicides in this family are postemergence contact herbicides that are activated by sunlight to form active compounds that disrupt the plant cells causing disintegration of cell membranes and chloroplasts. Destruction of cell membranes results first in rapid desiccation of plant foliage (wilting), followed by necrosis, and eventual death of the plant. On bright sunny days herbicide injury symptoms can occur in one to two hours. Since bipyridyliums are contact herbicides, they are an excellent choice for burn down of annual weeds. Because of the limited translocation of this chemical within plants, underground root systems are not destroyed and perennial weeds usually regrow after their top growth has been destroyed.

Paraquat (Gramoxone, Cyclone)
Application Timing (wheat and barley): Preplant or preemergence in reduced tillage and no-tillage fields. Not labeled for application to emerged wheat or barley. Injury may result from misapplication, off-target drift, or tank contamination. This herbicide has no soil activity.
Injury Symptoms: Mottled yellowing of leaf tissue, wilting and rapid desiccation occurring soon after direct application. Necrotic spots can appear on leaves from droplet drift. The growing point on contacted plants may emerge green even though more mature leaf tissue is dead.
Site of Action: Activated by Photosystem 1 (PSI).

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