Three major herbicidal families have caused injury due to drift from nearby fields. Phenoxyacetic and benzoic acids are plant growth regulators, and bipyridiliums are vine desiccants.
AUXIN-TYPE
Synthetic auxin growth regulators
- Family: phenoxyacetic acid
- Example: 2,4D (many product names)
- Family: benzoic acid
- Example: dicamba (Banvel, Clarity)
- Crop Uses: small grains, corn, pasture
- Movement: downward through plant (phloem)
Injury by auxin-types -- fiddle neck
Potato Injury: As auxins, these promote cell enlargement in the vascular tissue resulting in clogging and inhibition of translocation. Plants exposed to phenoxyacetic acids exhibit twisting stems (epinasty) due to asymmetrical growth. Leaves will malform appearing cup-shaped, crinkled, strapped, and having parallel veins. Leaves of dicamba-exposed plants have a "fiddle-neck" appearance, or a folded or hooded appearance. Curling of some petioles and leaves may occur along with the puckered appearance. Symptoms may occur within a few hours to several days. Yields are reduced but there are little affects on tuber appearance.
CELL DESICCANTS
Cell Membrane Disrupters
- Family: Bipyridilium
- Example: Diquat (Diquat) and paraquat (Gramoxone)
- Crop Use: Potato vine desiccation
- Movement: None, contact herbicide
Potato Injury: By diverting electrons from photosynthesis, these compounds cause the formation of hydrogen peroxide which disrupts cell membranes. Drift injury of these potato vine desiccants appears as leaf speckling or necrotic spots on leaves.