Carryover injury on potatoes has been commonly observed from four major herbicidal families. Carboxylic acids are plant growth regulators, imidazolinones and sulfonylureas are both inhibitors of ALS/AHAS enzyme, and triazines are photosynthesis inhibitors.
Amino Acid Inhibitors
Synthetic Auxin Growth Regulator
- Family: Carboxylic acid or pyridine or picolynic acid
- Example: Clopyralid (Stinger) and picloram (Tordon)
- Crop Use: Small grains, corn, sugar beets, grass pastures
- Movement: Downward through plant
Potato Injury: Potato injury is similar to that from phenoxyacetic acids such as 2,4D. Typical symptoms are curling of young leaves, "fiddle-neck" leaf appearance. Tuber yields are greatly reduced. In addition, exposure may carry over into seed tubers and affect the following year's crop.
- Family: Triazine
- Example: Atrazine (several product names), cyanazine (Bladex), simazine (Princep), hexazinone (Velpar)
- Crop Use: Corn and alfalfa
- Movement: Upward from root to vine
Potato Injury: Carry-over injury has generally occurred in Nebraska when metribuzin at its high, labeled rates is also used on a field after triazine-treated corn in Nebraska. Recommendations are to use metribuzin at half rate under this circumstance or to plant a variety that is resistant to triazine injury such as Russet Norkotah. Symptoms are the same as those described for metribuzin (Lexone, Sencor). The most notable early symptom is veinal chlorosis.
AMINO ACID INHIBITORS
- Family: Imidazolinone
- Example: Imazethapyr (Pursuit), imazaquin (Scepter) and imazamox (Rapture)
- Family: Sulfonylurea
- Example: Chlorimuron (Classic), chlorsulfuron (Glean), metsulfuron (Ally),
- nicosulfuron (Accent), and triasulfuron (Amber)
- Crop Use: Corn, soybean, small grains, grass pasture, and CRP
- Movement: Throughout plant
Injury by Sulfonylurea carryover -- tuber
Potato Injury: Foliar symptoms include a light green appearance of leaves especially new ones. Leaves are cupped upward giving a "boat-shaped" appearance. There may be a loss of leaf blade integrity; leaf disintegrates leaving the mid-rib and about 10% of a normal leaf. Rolling of the leaves may occur resembling drought stress. Severe injury results in stunting and purpling. Tuber yield and quality are greatly reduced.
TUBER SYMPTOMS ASSOCIATED WITH HERBICIDE INJURY
Tuber mis-shaping include longitudinal cracks, "dumb-bells," curved or folded tubers, indentations, and knobs, bumps or protrusions. Tubers are often under-sized. The skin may develop "alligator hide." Severe injury may cause tuber "chaining" and formation of "popcorn" tubers. Aerial tubers have also been observed.