Photo of several zucchini plant leaves in a crop field. the leaves have small light brown spotsClose up photo of a pea plant growing in a greenhouse with large white spots on the leaves

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WSSA Group Numbers

14 and 22

Where Used

Cropland, residential areas, and roadsides.

Common Active Ingredients

Group 14: saflufenacil and sulfentrazone; Group 22: paraquat and diquat

Effect On Plant

These herbicides destroy cell membranes which leads to the breakdown of cells. The two groups disrupt cell membranes and move in the plant differently, so symptoms are distinct. Group 22 herbicides are highly toxic, destroy cells on contact, and are therefore not translocated. Group 14 herbicides are translocated within the plant in the xylem and affect older leaves.'

Injury Symptoms

Photosystem I electron diverters (Group 22): Injury appears within hours. Where the herbicide contacts leaves, water-soaked spots appear followed by browning and necrotic spots or blotches (Figure 20).
PPO Inhibitors (Group 14): Symptoms of injury usually occur first in developed leaves. Symptoms appear as white necrotic areas on leaves (Figure 21) but then turn reddish brown and necrotic. Often the symptoms appear on leaf tips.

 
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