Herbicide Injury Symptoms

Pigment Inhibitors

Common Herbicides in the Group:

• norflurazon (Solicam, Zorial, Evital)

• fluridone (Sonar, Brake, Pride)

• clomazone (Command)

• amitrol (Amino Triazole)

How Applied:

Soil applied, water applied (floridone) or foliar (amitrol).

Movement in the Plant:

Move with water and nutrients in the xylem, except for amitrol which moves in both the xylem and phloem.

Mode of Action:

Prevent the production of the yellow carotinoid pigments. The carotinoid pigments of plants protect or buffer the green, photosynthetic plant tissue from overloads of light energy. When light is absorbed by the leaves and the carotinoid pigments are not present to protect the chlorophyll, high energy products build up and the chlorophyll is destroyed. When chlorophyll is destroyed and there is no underlying yellow pigment, the remaining leaf tissue is white.

Common Symptoms:

Albino or bleached appearance to foliage.

Effects of Pigment Inhibitors:

The white seedling leaves of these emerging corn plants are typical of the injuiry of plants emerging from soil treated with a pigment inhibitor. The herbicide used here was norflurazon. Note the green chlorophyll which was protected in leaf tips. These plants died within a few days.

These almond leaves have whitened veins as the result of exposure to norflurazon in the root zone. The herbicide was transported with water and nutrients foom the soil to the leaves where it is concentrated near the leaf veins, producing the typical whitening. Often a purple color is associated with the white symptoms.