Herbicide and Nonherbicide Injury Symptoms on Spring Wheat and Barley

Seedling Growth Inhibitors
The seedling growth inhibitors used in small grains include the thiocarbamate and dinitroaniline herbicide families. These herbicides interfere with development of seedlings as they emerge from the soil. They are soil-applied herbicides that require incorporation to be effective. Plants continue to take up the herbicide until after they have emerged from the soil. If plants emerge from the treated soil uninjured, they are likely to remain so. Seedling growth inhibitors are active at two sites, the developing shoot and the root. Root-inhibiting herbicides stop plant cell division, which in turn inhibits shoot elongation and lateral root formation. Uptake of these herbicides is through developing shoots and roots. Translocation of the herbicide is limited within the plant, and therefore the injury is mainly confined to the uptake areas. Shoot-inhibiting herbicides are absorbed by developing shoots and roots and are transported via the xylem and phloem to areas of new growth.

Triallate (Far-Go)
Application Timing (wheat and barley): Preplant incorporated in the fall or spring; preemergence incorporated in the spring. Barley has more tolerance to Far-Go than wheat.
Injury Symptoms: Injured small grain seedlings may show reduced coleoptile length, stunting, or delayed emergence. Shoot tips may also fail to unroll from the coleoptiles giving the plant a buggy-whip appearance. Plant injury is increased when Far-Go is incorporated too deeply into the germinating zone of the small grains. Tank mixes of Far-Go + Treflan can result in increased crop injury if applied to soils that are excessively wet and cool. See photos 15, 16, and 17.
Site of Action: Specific site(s) unknown; believed to have multiple sites of action.

Photo 15 Far-Go injury to spring wheat. Note the uneven emergence and stunting.

Photo 16 Far-Go can cause shoot tips to fail to unroll from the coleoptiles, giving the plant a buggy-whip appearance.

Photo 17 Wheat leaves emerging through the side of the coleoptile caused by high application rate of Far-Go.

Trifluralin (Treflan)
Application Timing (spring wheat and barley): Wheat, preplant incorporated in the fall and preemergence incorporated in the spring; barley, preplant incorporated in the fall or spring and preemergence incorporated in the spring.
Injury Symptoms: Injured small grain plants will exhibit shortened, swollen root tips giving them a "club-like" appearance; reduced lateral root growth will also be visible. Injured grass shoots are thick, short, and may appear red or purple in color. Injury is more severe if Treflan is incorporated too deeply (>1.5 inches) into the seeding zone (2 to 2.5 inches) of wheat or barley. Tank mixes of Far-Go + Treflan can result in increased crop injury if applied to soils that are excessively wet and cool. Numerous environmental factors such as high soil salinity, soil compaction, drought, heavy rainfall followed by soil crusting, or cold wet soils can stress plants, accentuating the injury effects of Treflan. See photo 18.
Site of Action: Tubulin protein involved in cell division.

Photo 18 Trifluralin injury to wheat. Note the shortened, swollen root tips.

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