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.

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.


  • 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

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 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.