Illinois Field Crop Applicators Practice Test

Which of the following is NOT a symptom of growth regulator herbicides?

1. Cupping of leaves

2. Interveinal chlorosis

3. Stalk bending

4. Twisting

The correct answer is: Interveinal chlorosis

Interveinal chlorosis is characterized by yellowing between the leaf veins, often signaling nutrient deficiencies, particularly in the case of iron deficiency. This symptom is not typically associated with growth regulator herbicides. Growth regulator herbicides primarily affect plant growth by mimicking natural hormones, leading to distinctive symptoms such as cupping of leaves, stalk bending, and twisting. These symptoms result from the herbicides' interference with normal plant growth processes, causing abnormal growth patterns. In contrast, cupping of leaves results from the herbicide causing uneven growth between different parts of the leaf, while stalk bending and twisting are direct manifestations of distorted growth responses to the herbicide. Thus, while interveinal chlorosis indicates a nutritional issue rather than a response to growth regulators, the other symptoms are common reactions to such herbicides.