University of California
Herbicide Symptoms

Acetyl CoA Carboxylase (ACCase) Inhibitors


WSSA Group: 1

ACCase Inhibitors are primarily used for postemergence grass control in broadleaf crops.

These herbicides are absorbed through the foliage and translocated in the phloem to the growing point, where they inhibit meristematic activity. ACCase Inhibitors include herbicides belonging to Aryloxyphenoxypropionate (FOPs), cyclohexanedione (DIMs), and phenylpyrazolin (DENs) chemistries. These herbicides inhibit the enzyme acetyl-CoA carboxylase (ACCase), which catalyzes the first step in fatty acid synthesis and is important for membrane synthesis. In general, broadleaf species are naturally resistant to FOPs, DIMs, and DENs herbicides because of a less sensitive ACCase enzyme. However, ACCase inhibiting herbicides may cause symptoms on certain broadleaf crops. Natural tolerance of some grasses is due to a less sensitive ACCase enzyme or a higher rate of metabolic degradation.

Injury Symptoms: Symptoms on sensitive plants may vary depending on the crop, rate of exposure, and growth stage. Injury symptoms caused by the ACCase Inhibitors appear several days after treatment. Symptoms include chlorosis (yellowing) of newly formed leaves with possible reddening or purpling of older leaves. Tissues at the growing point turn brown and eventually decompose (rotten growing point), a symptom called deadheart. These herbicides may cause general chlorosis and necrosis (white to shiny appearance). Lower exposure rates may cause interveinal bleaching (white) or chlorosis. In corn and sorghum, bleaching is more intense on whorl leaf. In broadleaf plants, symptoms include chlorosis, mottled chlorosis, necrotic spots, leaf crinkling, and leaf distortion.

Chemistry Group and Common Names of ACCase Inhibitors
Used in the United States

Chemistry Common Name
Aryloxyphenoxypropionates (FOPs) Cyhalofop-butyl
Cyclohexanediones (DIMs) Clethodim
Phenylpyrazoline Pinoxaden
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