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Grapevine Sensitivity to Herbicides: Avoiding Herbicide Damage

Grapes are hyper-sensitive to certain herbicides at very low concentrations. While many herbicides applied directly to grapevines can have a damaging effect, there are particular herbicide classes that are damaging to grapevines at very low levels. Growth regulator herbicides in concentrations 100 times lower than the recommended label rate have been reported to cause injury to grapes. This includes chemical classes such as the phenoxys (includes 2, 4-dichlorophenoxy acetic acid (2, 4-D) and MCPA) and benzoic acids (dicamba) and pyridines (triclopyr). The most common group cited to cause damage is the phenoxy herbicide group, which includes such ingredients as 2,4-D. Be aware that 2, 4-D is not a product name but a chemical ingredient a many different herbicide products!

Grapevine exposure to herbicides can occur with inappropriate use of herbicides within or outside of the vineyard. All pesticides must be applied according to regulations on the label. The product label is the law! Be sure to read and consult labels to determine if the product is registered for use with grapes and how to best apply the product. Labels generally have a section General Use Precautions and Restrictions. Some chemicals that are sensitive to grapes will have a precaution statement indicating the sensitivity to grapes and other plants/crops.

Identifying Harmful Herbicides – Know your active ingredients!
It is important to be able to identify the major classes of herbicides that cause damage to grapevines. Within these classes, there are multiple chemicals, or active ingredients, that cause problems in grapevine growth. It is important to have knowledge of which herbicides are commonly used on major production crops in Oregon, as your vineyard may be surrounded by other agricultural production or areas of risk. For example, 2, 4-dichlorophenoxy acetic acid (2, 4-D), a growth-regulator herbicide that is harmful to grapes, is registered for use on major agronomic crops in Oregon, as well as rangeland. It is important to note that these same herbicides are often used in managed forests, hobby farms, stables/pastures, parks, and residential areas and may pose a potential risk. The table below indicates the various herbicide classes that can damage vineyards. Growth regulator herbicides are often the most commonly found related to herbicide drift damage.

Click on the thumbnail to view details of the table below. This table provides information such as the Herbicide Resistance Action Committee (HRAC) code, chemical family, active ingredients, and crops or applications for which the herbicides are generally used. This is an abbreviated reference table that is intended to assist you understanding which herbicides can be damaging to grape as well as avoiding these herbicide formulations when choosing an herbicide. Be sure to avoid using these products in and around vineyards during stages at which grapevines are susceptible to damage.

Herbicide classes and active ingredients damaging to grapevines at low concentrations

Herbicide classes and active ingredients damaging to grapevines at low concentrations

Understanding Herbicide Classifications
Herbicides belong to different chemical classes based on their chemical properties and modes of action in damaging weeds or plants. It is important to know the specific compounds of which grapevines are most sensitive. Because there are so many herbicide products and brand names available, it is important to be able to identify herbicides classes and active ingredients that damage grapevines at very low levels. For example, if you know that one product brand contains active ingredients that damage grapes, you want to be sure to switch to another product that does not contain that same active ingredient or any other chemical that has the same chemistry by which may also be damaging to grapes. Be sure to look for the HRAC classification code and chemical class. Herbicides are grouped by these codes for easy identification of a compound, and this can help you identify products that may have potentially harmful active ingredients. Click the thumbnail below to learn more about how herbicides are categorized.

Click on the thumbnail to learn more about how herbicides are categorized.

Click on the thumbnail to learn more about how herbicides are categorized.

Herbicide Drift
Drift is defined as the movement of herbicides off of the target (or site) by which they were applied. This is generally unintentional. It is important to be aware of drift in and around vineyards since grapevines are more sensitive to herbicides than other crops. Not all herbicides are equally damaging to grapes, and vineyard production often requires herbicide use to control weeds. However, incorrect herbicide selection or inappropriate application can lead to damage. Furthermore, herbicide drift from other sites can damage foliage, shoots, flowers, and fruit in grapevines, and cause significant economic loss.

For more information about herbicide drift damage in vineyards, please see the following links:
Preventing Herbicide Drift and Injury to GrapesGet Adobe Acrobat Reader
Phenoxy Herbicide Damage to Grapevines

Reduce Vineyard Herbicide Exposure
There are various ways in which to reduce vineyard exposure to herbicides. Product labels generally include a section on Spray Drift Management to avoid chemical damage on non-target plants and sensitive crops.

Drift reduction methods include the following:
1. Avoid on-site damage by using the correct product and avoid direct contact with vines!
2. Increase spray-droplet size. This can be achieved by adding a spray thickener or adjuvant, using low spray pressures, and drift-reduction nozzles such as flood-type nozzles.
3. Avoid spraying during windy days (>5 mph).
4. Avoid spraying during days with high temperatures as chemicals can volatilize more readily. Avoid temperature inversions which occur when temperatures are cooler closer to the ground and increase with altitude (ground fog).
5. Avoid the ester form of herbicides, and opt for amines and metallic salts. “Low volatile” (LV) esters are still more volatile than these other compositions of herbicides.

It is the responsibility of the applicator to avoid spray drift or volatility! Proper equipment, weather conditions and precautions need to be considered by applicators prior to spraying an herbicide. If you are concerned about potential damage from off-site herbicides applications, contact your neighbors about your concerns and pass along educational information to them

How to Prevent Herbicide Drift
Herbicide drift can be prevented or minimized through knowledge of herbicide use and regulations, careful management, and communication with neighbors.

It is critical to use the appropriate herbicides in the vineyard, and avoid applications of those herbicides known to be damaging to grapevines at low concentrations (e.g. phenoxy, dicamba, etc) unless applying them when vines are dormant. Communicating vineyard sensitivities to neighbors is critical!

To avoid herbicide damage coming from applications outside of the vineyard, communicate with your neighbors and establish a good relationship with them. If your vineyard is surrounded by other crop-growing areas, make sure your neighbors know when grapes are in their most sensitive growth stages from bud-break through bloom and request that they refrain from applying certain herbicides during that time and/or use other formulations of the product, such as amine rather than ester formulations of products, particularly 2,4-D.

Read the label!
Read herbicide labels prior to purchase and use. Always use products according to the label directions. Herbicides that contain active ingredients that grapes are hyper-sensitive to, often contain a caution statement. Refer to Table 1 above to identify herbicide ingredients that are particularly damaging to grapevines. Also, only use herbicides that are registered for use in Oregon. A safe bet is to use herbicides that are registered for use with grapes.

Determining herbicide use and registration
If you are uncertain of whether a certain chemical is registered within the state of Oregon and particularly for grapes, you can search a pesticide database. This provides additional information on the herbicide product including what crops they are registered for and their intended use. You may narrow your search by crop, pest, or ingredient. Follow the easy and brief tutorial to learn how to use the herbicide search site.

Reporting Herbicide Damage
The Oregon Department of Agriculture (ODA) works in conjunction with the Environmental Protection Agency (EPA) to regulate herbicides. The EPA has the main responsibility for regulating the manufacture, distribution, sale, and use of pesticides in the U.S. All pesticides must first be approved and registered by the EPA, and also with state governments. It is important to note that the EPA label is a legal document which must remain original and complete. If the pesticide is not used according to label directions (whether unintentional or not), it is a violation of federal and state law which can be penalized. The Oregon Department of Agriculture registers pesticides for use in the state. Any product that is not registered for use in Oregon cannot be used in the state.

Because herbicides are regulated, the ODA must enforce thier proper use. Therefore, the ODA Pesticides Division handles pesticide investigations, enforcement of regulations, and pesticide use reporting (PURS). If you suffer crop loss or damages as a result of suspected herbicide drift, you must file a pesticide loss report. This must be done as soon as possible after the damage has occurred. The ODA may choose to conduct an investigation, which will determine if a violation of state and/or federal pesticide laws occurred. This will not provide monetary compensation as the ODA cannot require someone to pay for a loss due to pesticide use.

For more information on the ODA Pesticide Division Herbicide Drift Investigations, please refer to the following resources:
Pesticide Laws and Regulations
Pesticide Investigations and EnforcementGet Adobe Acrobat Reader
Pesticide Loss ReportGet Adobe Acrobat Reader

General Vineyard Weed Management
Weeds can be effectively managed in vineyards using herbicides. Herbicide selection and application are important to effective control. For information on managing target weeds in vineyards, please visit the online Pacific Northwest Weed Management Handbook. Specific chapters include information for vineyard weed management. Keep in mind that different herbicides are registered for particular use in vineyards such as establishing and non-bearing. Be sure to follow guidelines outlined in this guide.

For general information on viticulture, vineyard establishment and weed management, see Oregon Viticulture, available for purchase at OSU Bookstore.

More information on vineyard weed management can be found in the Pest Management Guide for Wine Grapes in OregonGet Adobe Acrobat Reader.