Dicamba Injury to Winter Wheat

Fabian Menalled, Reviewed May 2004
Meghan Trainor, Posted May 2000

As field crops grow and mature, their tolerance to herbicide changes.　For this reason, it is critical that postemergence herbicides be applied at the proper time to achieve maximum weed control and minimum crop injury.
As a general rule, annual and biennial weeds are more susceptible to postemergence herbicides when they are in the seedling stage.　As weeds mature they become more difficult to control.　Also, field crops differ in the periods when postemergence herbicides can safely be applied.　This places the grower in the predicament of when to apply the herbicide in order to achieve the least crop injury as well as satisfactory weed control.　To minimize the risk of herbicide crop injury, each crop must be considered separately to determine the correct crop growth stage when applications could be done.　
Dicamba is one among many herbicides recommended for postemergence weed control in winter wheat.　Banvel, a benzoic acid, belongs to the chemical group of growth regulators.　Growth regulator herbicides can act at multiple sites in a plant to disrupt hormone balance and protein synthesis, thereby causing a variety of plant growth abnormalities.　Growth regulator herbicides are mostly absorved through the foliage but root uptake may also occur.　These herbicides can move in both the xylem and the phloem to areas of new plant growth and can be used to control perennial and annual broadleaf weeds.　However, Dicamba can injure winter wheat.　
The best time to apply Dicamba is in the early spring (February through April) after winter wheat has begun to tiller, but before the joint stage.　The plant develops additional stems during tillering, but the stems do not elongate.
From the seedling through the tillering stages all leaves appear to originate from the base of the plant.　During jointing, stems lengthen as recognized by leaves being attached at different joints (nodes) on the stem.　Although some herbicide labels allow for application up to the boot stage, delaying application of Dicamba beyond the joint stage will increase winter wheat injury and decrease weed control.
In conclusion, winter wheat can be treated with Dicamba in the spring after winter dormancy has been broken and before wheat begins to joint.　If Dicamba is applied to wheat in the joint stage, significant crop injury may occur.　Furthermore, injury in the joint stage will affect head development.


Yangzhou pioneer chemical CO.LTD