Grape Herbicide Injury

Herbicides are incredibly useful tools.  They save labor, money, and time.  However, misuse can have unintended consequences — sometimes minor and sometimes major.  Earlier this week I visited a small muscadine vineyard where an herbicide was obviously sprayed on the vines.  How do I know?  Because every last vine was completely dead.  The person I spoke with was not the manager of the vineyard so did not know the details of what applications were made and at what time, but that is an example of extreme herbicide misuse.  Most times though, the evidence is minor.  In grapes, we often see a condition called epinasty.  Epinasty is when a leaf exhibits unusual growth, usually elongation and downward curvature.  A common herbicide group that causes these symptoms on grapes are phenoxy herbicides.  This includes 2,4-D.  Often the source of the herbicide may be unknown, as drift can occur and hit an unintended target.  See the photo below on a muscadine leaf for evidence of herbicide injury:

Herbicide injury on muscadine

Herbicide injury on muscadine

Notice the “lettuce-like” appearance.  This is common with phenoxy herbicides.  The symptoms in the photo above are relatively minor and will not effect the vine.  For more information on herbicide injury and other leaf symptoms that may or may not be caused by herbicides take a look at this article: Grapevine Problems: Leaf Spots Not Caused by Insects or Disease

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