Article written by Madeline Wimmer, UMN Extension Fruit Production Educator
Images: Different herbicides lead to a range of symptoms in grapes including the fanning displayed on the left and shoe-stringing— a condition with the appearance of fabric puckering, or a tightened cupped look as seen on the right photo. Left photo credited to a Minnesota grower from Morrison County and right photo from a grower located in Washington County.
Grapevine foliage is highly sensitive to herbicide drift and tends to show more dramatic symptoms than some other crops. Experiencing drift, whether it originates from within or outside of a vineyard, can be a frustrating challenge for growers, and devastating when the damage is extensive.
What do herbicide damage symptoms look like?
Herbicide symptoms can vary depending on which type of herbicide is involved. Additionally, the amount, concentration, droplet form (i.e., particle vs vapor), and weather conditions at the time of drift also contribute to resulting symptoms.
Auxin herbicides: Some herbicides are formulated as plant growth regulators (PGR), also called auxin herbicides. These include 2,4-D and dicamba, as well as picloram, triclopyr, and clopyralid.
ALS-inhibitors: Inhibition of acetolactate synthase (ALS) is a different mode of action in herbicides trisulfuron-methyl, imazapyr, and chlorsulfuron, of which grapes are also sensitive.
EPSP synthase inhibitors: Glyphosate is a well-known herbicide that can cause injury in grapes and works by inhibiting EPSP synthase, an enzyme that plays a key role in creating plant proteins and other biochemicals.
While symptoms vary among different herbicides, some general trends exist, which are summarized in the table below.
Table: Herbicides, modes of actions, and symptoms as they show up on grapes*
*This table was created from information sourced from University of California IPM.
Drift vocabulary:
Understanding drift terminology can help you figure out what type of injury occurred in your vineyard.
Chlorosis: pale or yellow leaf color due to a lack of chlorophyll.
Epinasty: downward bending appearance of leaves due to faster growth on the upper side of the leaf than the bottom side.
Leaf feathering: abnormal growth on leaf edges that cause a feathered appearance on leaf margins.
Leaf strapping: unusual, stretched-look to a leaf, relative to its width.
Leaf stacking: leaves grow unusually close to a stem due to shortened internodes, making the foliage look compressed.
Mottled chlorosis: parts of a leaf appear chlorotic while other parts look normal.
Shoe-stringing: distorted leaves that appear both elongated and cupped, similar to fabric puckering that can happen when a thread’s tension is too tight within a piece of fabric.
Preventing drift
DriftWatch
DriftWatch is a resource that helps put vineyards on the map to alert pesticide applicators of their location. For those who have registered, it is still worth having conversations with neighboring farms and county highway departments to spread awareness.
To learn more about DriftWatch, check out their website:
Website: https://driftwatch.org/
Other ways to be proactive
Off-site drift
Additional steps to prevent herbicide drift include selecting growing sites that are not adjacent to row crop fields, which may be possible for new growers, or planting a buffer strip of trees on vineyard edges next to row crop fields.
On-site drift
To prevent injury from on-site herbicide applications, growers should be careful about which herbicides are applied at any given time of the year.
Certain herbicides should only be applied in vineyard blocks with mature grapevines, as they can injure younger grapevines with less woody growth. Some herbicides are systemic, whereas other herbicides are more local and can actually be used for managing grapevine suckers (the shoots that emerge from the grapevine base).
To learn more about ground and weed management for grape production, view the following resources:
Reporting and drift
Growers who have detected drift in their vineyard in Minnesota also have the option to report their findings to the Minnesota Department of Agriculture (MDA) to open an investigation. It’s recommended to start this process immediately, and can help put drift incidents on the map, with the option to pursue litigation when appropriate.
To learn more about filing a drift complaint to the MDA, look at their web page, “Pesticide drift complaint process and timeline.”
Additional resources
To view a gallery of herbicide drift symptoms, visit the University of California IPM’s Herbicide symptoms search engine.
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