Herbicide Injury Symptoms

Photosynthesis Inhibitors

Common Herbicides in the Group:

• atrazine (Aatrex)

• simazine (Princep)

• metribuzin (Sencor, Lexone)

• prometryne (Caparol)

• cyanazine (Bladex)

• diuron (Karmex, Diurex)

• linuron (Lorox)

• bromacil (Hyvar)

• tebuthiuron (Spike)

How Applied:

Mostly soil applied with some foliar activity.

Movement in the Plant:

Systemic and move primarily with water and nutrients in the xylem.

Mode of Action:

Inhibit photosynthesis by binding to a protein in the electron transport system thus effectilely blocking energy transport and causing a build up of destructive high energy products.

Common Symptoms:

Yellowed, chorotic leaves which may turn necrotic with excessive herbicide.

Effects of Photosynthesis Inhibitors:

The symmetrical triazine herbicides such as simazine and atrazine most commonly cause plants to exhibit interveinal chlorosis, initially the veins remain green and the interveinal regions are chlorotic. As the symptoms progress, interveinal areas, particularly around the leaf margins, become chlorotic. A range of simazine symptoms in almond are evident in this photo.

The asymmetrical triazine herbicides such as prometryne, the substituted urea herbicides such as linuron and diuron, and the uracil herbicides such as bromacil, commonly cause plants exposed to these herbicides to exhibit veinal chlorosis. Veinal chlorosis can be clearly seen on the bean seedling, there is also some marginal necrosis. This injury resulted after exposure to soil residues of linuron.