Pigment Inhibitors
WSSA Group Numbers
13 and 27
Where Used
Cropland, mainly to control broadleaf plants though some grasses are also susceptible.
Common Active Ingredients
Group 13: clomazone; Group 27: mesotrione, tembotrione, and topramezone
Effect On Plant
Pigment inhibitor herbicides cause chlorophyll to be destroyed. There are various ways this can occur, including inhibition of certain pigment production. The absence of these pigments allows excessive light energy to destroy chlorophyll, which causes visible leaf bleaching. Plants are unable to photosynthesize due to a lack of pigments, and they may die after their energy reserves run out.
Injury Symptoms
Leaves turn white and may look bleached (Figure 22), and this symptom may be most severe near the leaf veins while interveinal areas may remain green (Figure 23). Purpling of leaf edges may also occur. Leaves that grow after application or exposure may look crinkled.