Herbicide Injury Symptoms

Amino Acid Synthesis Inhibitors

Common Herbicides in the Group:

• glyphosate (Roundup, Rodeo, Accord)

• sulfosate (Touchdown)

• imazethapyr (Pursuit)

• sulfmeturon (Oust)

• chlorsulfuron (Glean)

• pyrithiobac (Staple)

How Applied:

Glyphosate and sulfosate are foliar applied while the others are mainly soil applied but do have foliar activity.

Movement in the Plant:

Glyphosate and sulfosate move readily in the phloem tissue with photosynthate or mobilized storage products, the others move in both xylem and pyhloem tissue.

Mode of Action:

These herbicides inhibit enzymes critical to the production of certain amino acids. Amino acids are important building blocks in the production of proteins. Proteins are important structural components, constituents of cell membranes and as enzymes are regulators of metabolic processes. When amino acid production stops, plant growth decreases and finally is stopped.

Common Symptoms:

Because so many plant processes are affected, many symptoms can be produced including stunting, chlorosis, reddening, and distortion of terminal growth.

Effects of Amino Acid Synthesis Inhibitors:

The corn plant on the left had been treated with a foliar application of imazethapyr ten days earlier. Note the stunting and purple color of the stem.

The bean plant on the left is stunted with chlorotic leaves from treatment with glyphosate 14 days earlier.

The walnut stem here displays the effect of a glyphosate treatment made several months earlier. Note the proliferation of growth from the buds at each internode.