Herbicide and Nonherbicide Injury Symptoms on Spring Wheat and Barley

Photosynthetic Inhibitors
The nitrile herbicide family is the only photosynthesis inhibitor labeled for spring wheat and barley. The nitriles, Buctril and Bronate herbicides, are primarily used for control of annual broadleaf weeds in small grains. The nitrile herbicides are contact herbicides that close the photosynthetic (food producing) process in susceptible plants by binding to specific sites within the plant's chloroplasts. Injury on susceptible broadleaf weeds appears first as blistered lesions on leaves that eventually become necrotic within a 24-hour period. Since the nitriles are classified as contact herbicides, they are not translocated within the plant and good foliar coverage is essential for good weed control. There is no soil activity with the nitrile herbicides.

Bromoxynil (Buctril, Bronate, Bison, Moxy)
Application Timing (wheat and barley): Postemergence from emergence until the boot stage. Spring wheat and barley have good tolerance to Buctril.
Injury Symptoms: Injury symptoms from Buctril on small grains appears as leaf tip chlorosis, general wilting, and necrotic leaf spots. Crop injury from Buctril on small grains is uncommon, but can occur if application is made during abnormally cool temperatures or when high temperature or humidity follows application. Crop injury on small grains is short lived and recovery is generally rapid. See photos 13 and 14.
Site of Action: D-1-quinone-binding protein of photosynthetic electron transport.

Photo 13 Bromoxynil can cause small grain injury under adverse weather conditions

Photo 14 Bromoxynil injury to spring wheat. Note the necrotic leaf spot. Injury is temporary and small grains quickly recover.

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