What defines the leaf symptoms caused by Dicamba?

The symptoms caused by Dicamba are characterized primarily by epinasty followed by necrosis. Epinasty refers to the downward curling of leaves due to the differential growth rates of the upper and lower surfaces, often caused by a hormonal imbalance in the plant. This type of damage is typical of herbicide exposure, particularly from those in the synthetic auxin class, like Dicamba. Following the initial epinastic response, necrosis can occur, which is the death of plant cells leading to tissue browning. This symptom progression is crucial as it helps identify exposure to Dicamba specifically, especially in sensitive crops.

The other options describe different types of leaf symptoms that may be associated with various stresses or diseases. Browning and pocking often indicate mechanical damage or specific pest activity, while bleaching and purpling could relate to nutrient deficiencies or other herbicide effects not linked to Dicamba. Chlorosis and mottling usually signify issues with nutrient uptake or disease. Thus, the manifestation of epinasty followed by necrosis is distinct and a clear indicator of Dicamba's physiological impact on plants.