Grape and Pasture Herbicides

Grape is sensitive to auxin-type herbicides. Off-target damage can lead to delayed harvests, reduced productivity for growers, and bad publicity for the industry. The extent of damage depends on level and timing of exposure, crop cultivar, and management practices. 
Management aids are available to help prevent and diagnose off-target herbicide injury to grape.
Preventing Herbicide Injury in Grape
Herbicide selection- follow label use directions and precautions, understand herbicide characteristics such as volatility, water solubility, persistence, and efficacy.
Drift prevention- know weather conditions for minimizing drift potential, proximity to sensitive crops, proper application timing, nozzle selection, and sprayer set-up.
Sprayer contamination- to best avoid injury from contamination, dedicate a sprayer for pasture-use only
Field selection- risk assessment based on topography, surface water, field history, and future plans for field.
Monitoring results- field number or name, date and rate of application, weather conditions.
Diagnosing Herbicide Injury in Grape

Many herbicides used in pastures and hay fields are growth regulators that mimic the plant hormone auxin. When observing herbicide damage in grape, it is often difficult to distinguish between these herbicides. The symptoms shown below can help to identify certain characteristics of each of these herbicides in grape. The following are descriptions of commonly observed symptoms resulting from grape exposure to synthetic auxin herbicides:

Curling- folding of edge of leaf margins.
Epinasty- twisting, bending and/or elongation of stems and leaf petioles.
Chlorosis- yellowing or whitening of leaves resulting from loss of chlorophyll.
Necrosis- browning of tissue resulting from cell death.
Herbicides Evaluated for Symptomology on Grape
Common Name Chemical Family Trade Names
aminocyclopyrachlor* Pyrimidine-carboxylic acid Not registered for use in pastures and hay fields
aminopyralid Pyridine-carboxylic acid Milestone, ForeFront R&P, ForeFront HL, GrazonNext HL
picloram Pyridine-carboxylic acid Tordon, Surmount, Grazon P+D
2,4-D* Phenoxyacetic acid Various names and mixtures
dicamba Benzoic acid Banvel, Clarity, Oracle, Rifle, Brash, Rangestar, Weedmaster
*Products containing aminocyclopyrachlor are registered for non-cropland use, but are not yet registered for use in pastures. 
**Picloram, aminopyralid, and dicamba are often sprayed in combination with 2,4-D.
Time Lapse Videos

Grape plants were grown in a greenhouse and treated with simulated drift rates for aminocyclopyrachlor, aminopyralid, picloram, dicamba and 2,4-D. Plants were allowed to dry and moved indoors under artificial light. Photographs were captured every hour for twelve days. Images were then compiled to create a time-lapse video showing the development of symptoms.


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Description: At 1 day after exposure, aminocyclopyrachlor (MAT28) and picloram plants exhibited slight petiole drooping and leaf curling. New growth had essentially ceased by 6 days after exposure in MAT28 and picloram plants. New growth on the aminopyralid plant had distinct upward cupping by 10 days after exposure.

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Description: Grape plants showed early symptomology after exposure to 2,4-D and dicamba. Petioles were severely bent and leaves were folded by 2 days after exposure. New growth had ceased by 5 days after exposure. By 12 days after exposure, both plants had chlorotic and necrotic symptoms.

Symptomatic Still Images
Petioles drooping and folding of 
new leaves
Curling and cupping in young 

 Severe epinasty and chlorosis 
with high rates new leaves
Moderate epinasty and slight leaf curling
Chlorosis and more pronounced cupping of youngest leaves

Clustering of bud leaves at 1 monthAdvanced chlorosis and epinasty with low rates
Epinasty in stems and leaf petioles
Petioles drooping, leaves folded, and early necrosis with high rates

Upward cupping of young leaves with low rates
Severe epinasty and leaf folding
Downward folding in older leaves and petioles bending

Fan shaped and sharp points in young leaves
Drooping petioles and folded young leaves
Cupping in new leaves with low rates

Chlorosis and necrosis with high rates