Lipid Synthesis Inhibitors

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WSSA Group Numbers

1 and 8

Where Used

Cropland – most often applied to control grassy weeds

Common Active Ingredients

Group 1: sethoxydim, clethodim, and quizalifop; Group 8: triallate.

Effect on Plant

Lipids are essential to production of cell membranes; inhibiting lipid synthesis interferes with plant growth in roots and shoots because new plant growth stops. These herbicides stop the waxy cuticle from forming properly and they may cause cells to develop abnormally or inhibit cell division. Within this mode of action, the two main groups of herbicides are absorbed and moved through plants differently. Group 1 herbicides are usually applied to the foliage and move in the phloem to growing points. Group 8 herbicides are usually soil-applied and are absorbed in roots and emerging shoots and aretranslocated only in the xylem. 

Injury Symptoms

In grasses symptoms vary based on herbicide group and whether the herbicide was applied to soil or leaves. Group 8 herbicides cause leaf blades of grass to not fully emerge from stem. Grass seedlings may not emerge from the soil. On susceptible broadleaf plants, roots are thickened, shortened, and may have a clubbed shape.Cotyledons may be enlarged, while true leaves are smaller than usual and dark green. Group 1 herbicides have different symptomology and mostly affect grasses. These herbicides tend to accumulate at the growth point (the meristem), and this part of the plant will often bleach white and then rot, making it easy to pull the growth point away from the rest of the plant (Figure 1). The ends of leaf blades may look bleached (white), purple, or chlorotic. Broadleaf plants are usually tolerant to these herbicides, but may show symptoms of chlorotic or necrotic spots if they are injured by solvents in the herbicide formulation (Figure 2).