Seedling Growth Inhibitors

Click on an image to view as a slideshow.

WSSA Group Numbers

3, 15, and 29

Where Used

Cropland, home gardens, and roadside settings to control both grasses and broadleaf plants.

Common Active Ingredients

Group 3: trifluralin; Group 15: pyroxasulfone and metolachlor; Group 29: indaziflam.

Effect on Plant

This mode of action inhibits cell division at growing points of developing seedlings. Roots and shoots of seedlings do not develop correctly, and plants may die because seedings are not able to take up adequate water and nutrients from the soil. Seedling growth inhibitor herbicides are applied pre-emergent and absorbed in the roots and/or shoots of emerging seedlings when they contact the herbicide in the soil. These herbicides do not translocate very far in the plant.

Injury Symptoms

In croplands, poor stand emergence and stunted seedling growth may be the first non-target injury symptoms that appear. Typically, only seedlings show symptoms while plants that are established at the time of application do not show signs of injury. For group 3 herbicides typical symptoms include roots that are thickened at the tip and swollen stems (Figure 9). Plants are severely stunted, and root systems are poorly developed (Figure 10). Stems may be brittle and break off at the soil surface. Nutrient deficiency or drought symptoms may be present due to poor root development or leaves may appear crinkled.

Group 15 herbicides show symptoms on plant shoots including “buggy-whipping,” where shoots fail to emerge from the whorl of the plant. Other symptoms include enlarged cotyledons and stunting, crinkling, and darkening of true leaves.