Monday, June 30, 2014

Many Reports of ALS Herbicide Injury in the Burrus Footprint

ALS herbicides are one of the more common sources of herbicide injury this year.  Products in the ALS family tend to be registered for use in only corn or only in soybeans (occasionally both, but more often one or the other).  Therefore, either corn or soybeans can be exposed to this herbicide via carryover, misapplication, or tank contamination.

ALS or acetolactate synthase is an enzyme that is needed to form amino acids in the plant.  The application of ALS herbicides ties up this enzyme, which means the plant is not able to form amino acids.  Amino acids are needed to form proteins, and proteins are the building blocks of just about everything.  This means that plant is not able form proteins, which means that plant cannot form the materials needed for cell growth. 

When this herbicide is applied to a plant, it moves both the up and down within the plant, then settles in the growing points. The ALS enzyme is shut down rapidly by these products, but actual symptoms do not appear until 10 days later when the plant begins to tap out its protein reserves.  Death, if it is going to occur, will occur within 10 to 14 days.  It is not uncommon for ALS products to have a several month interval between application in one crop and rotation to the next crop.

 Symptoms of injury in corn can include all or a few of the following:  Plants may be stacked, or there is no space between the nodes.  Leaves should be placed alternately on the corn plant, but a stacked plant (lacking internode length) appears to have opposite leaves.  Likewise, the lack of space between the nodes means the plant may appear shorter than an otherwise healthy plant.  Such stunting may be dramatic.  Leaves may take on a yellow or even purplish yellow cast due to lacking chlorophyll formation.  In many cases, the midrib of the plant will take on a stark dark purple or red appearance.  Because roots also have growing points and because growth at these points may be inhibited by ALS products, stubby or bottle-brushed root deformation is a possibility.

Symptoms of injury in soybeans will parallel those in corn, but the nature of the plant may cause those symptoms to look less similar.  For instance, stacking does occur, but this causes the bean plant to appear “bushy” due to lacking stem elongation.  Leaves will also yellow, and the veins on the underside of the leaf will also appear red, brown, or purplish in color.

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