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Practical Weed Science for the Field Scout: Corn and Soybeans
Pigment inhibitors
Injury from clomazone on soybeans and corn. Soybeans are generally tolerant; damage to soybeans is unlikely except at high application rates.
Isoxazolidinones chemical group
Herbicides
- Clomazone (Command — soybean, rice)
Mode of action and characteristics of activity
- Specific sites unknown
- Control of annual grass and broadleaf weeds
- Primarily soil active
- Medium soil persistence
- Volatile, be aware of drift potential
General symptoms
- Leaf and stem tissue turns white after becoming translucent at the leaf tips, then chlorotic and necrotic. In corn, if more than 75 percent of the plant is white, it will probably die.
Injury from isoxaflutole on soybeans appears to be similar to atrazine injury except that isoxaflutole causes more chlorosis and some bleaching should eventually be seen.
Injury from isoxaflutole on corn. Note the chlorosis on leaf tips and ends.
Isoxazoles
Herbicides
- Isoxaflutole (Balance — corn)
Mode of action and characteristics of activity
- Inhibition of p-hydroxy phenyl pyruvate dioxygenase. Control of annual grass and broadleaf weeds
- Primarily soil active
- Medium soil persistence
General symptoms
- Plant tissue turns white, chlorotic, and then necrotic
- Subsequent rainfall events will result in plants taking up more herbicide and showing injury symptoms in newly developed tissue
- Injury can be severe in sandy soils, in high-pH soils, in combination with high application rates of atrazine, and under cool, wet-weather conditions
Injury from postemergence applications of triketone herbicides like mesotrione will appear as irregular chlorosis and bleaching of the lower leaves and whorls. Some sweet corn hybrids are highly sensitive to postemergence triketone herbcides.
Injury from residual activity of triketone herbicides like mesotrione will also appear similar to isoxaflutole and atrazine injury with initial chlorosis of the first true leaves and trifoliates, but some signs of bleaching should eventually appear.
Soybean injury can occur as a result of mesotrione or topramezone carryover. This will appear as partially bleached trifoliates with some degree of leaf strapping.
Mesotrione injury on other vegetable plants will also appear as bleaching, especially toward the outer leaf edges.
Injury from drift of triketone herbicides like mesotrione on soybean plants ranges from slight bleaching of the leaf margins to severe chlorosis and bleaching of the newest trifoliates, depending on the severity of drift or contact with the foliage.
Triketones chemical group
Herbicides
- Mesotrione (Callisto — corn)
- Topramezone (Impact — corn)
- Tembotrione (Laudis — corn)
Mode of action and characteristics of activity
- Inhibition of p-hydroxy phenyl pyruvate dioxygenase
- Control of annual broadleaf and some grass weeds
- Soil and foliar activity
- Medium soil persistence
General symptoms
- Plant tissue turns white (bleaching) then necrotic within three to five days
- Translocates in xylem and phloem
- Injury can be worse under cool, wet weather conditions
IPM1007, revised June 2007
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