Burndown Herbicides, Drift, and Vineyards

Background of the Issue

In the past, we have received calls asking for burndown herbicide suggestions for fields that are adjacent to sensitive crops such as vineyards or specialty crops. Most broadleaf plants (e.g., grapes, vegetables, fruit crops, ornamentals, certain trees, non-tolerant soybeans, tobacco, etc.) are extremely sensitive to plant growth regulator (PGR) herbicides. PGR herbicides include phenoxy, benzoic, and pyridine classes of compounds. The most common PGR herbicides used are those containing 2, 4–D, or dicamba. But others, which have been documented as causing injury include picloram (e.g., Tordon), triclopyr (e.g., Garlon), and clopyralid (e.g. Stinger). All the PGR herbicides should be considered as potentially injurious to non-target sensitive plants as a result of spray drift. Herbicide formulations and vapor pressure are primary factors associated with the volatility of most PGR herbicides. In general, the higher the vapor pressure of a pesticide, the greater its tendency to volatilize. Unfortunately, it is difficult to simply use their vapor pressure values to determine how much volatility will occur and thus cause off-target movement and injury. Many factors, including environmental issues, play a part in the overall potential for herbicides to volatilize. Temperature and relative humidity are important for volatility – high temperatures and very low relative humidity usually cause much more volatility. Though volatility is important, off-target movement of herbicides is also due to small spray droplet drift and/or temperature inversions.

Historically, many of the standard burndown herbicide programs have included 2,4-D, primarily to control glyphosate/ALS-resistant marestail and other weeds such as dandelion and winter annuals. And with more XtendFlex and Enlist E3 soybean varieties being sold, dicamba- and 2,4-D choline-products, respectively, are being used more in burndown programs. However, if crop production fields are near sensitive crops or areas, both herbicides have the potential to cause problems even early in the season if grapes or sensitive trees are starting to bud or break dormancy. Furthermore, glyphosate drift can cause problems in these settings, and glyphosate-resistant weed species will not be controlled. In cases like this some alternative herbicides for burndown include paraquat (e.g., Gramoxone), glufosinate (e.g., Liberty 280), saflufenacil (e.g., Sharpen), and tiafenacil (Reviton). And depending on the type of weeds being controlled, other herbicide options (or their generic alternatives) such as Basis Blend, Harmony Extra, Canopy DF, metribuzin, Lorox, or others can provide some burndown activity. To improve the effectiveness of these products, especially during early spring conditions, make sure to use higher rates, include necessary adjuvants, use higher spray volumes (≥15 gpa), spray when weeds are small (3-5" tall) and actively growing; and apply during sunny days and warm temperatures (>50°F daytime). Most of the soil applied residual herbicides that are tank-mixed with burndown herbicides are not volatile and usually don't cause problems to sensitive crops (unless severe drift occurs). However, no matter what herbicide is being applied it is best to keep the spray in the target area by using low-drift nozzles, spraying in low wind conditions, and applying when the wind direction is away from the sensitive area.

An article from Dr. Kevin Bradley and his colleagues at the University of Missouri noted that even when using PGR herbicides during the early spring, some reports of dicamba drift occurred to specialty crops and trees. Refer to his article for more details.

Communication is key to help reduce the chances of herbicide drift. 

DriftWatch by FieldWatch is now available to use in Pennsylvania. It is a free, online Voluntary Specialty Crops Registry designed to alert applicators about locations of sensitive areas. The stewardship tool allows for improved communication and collaboration between producers of specialty crops and pesticide applicators using a technology platform where producers can map their sites and provide contact information to pesticide applicators through an online mapping system.  Go to the FieldWatch site for more details and to register. Please consider using this new tool to help reduce the issues with drift. It is not a regulator tactic but simply a means to be a better neighbor.

Considering PA Vineyards

While the grape and wine industry may be small in acreage relative to other sectors of agriculture, Pennsylvania ranks fifth in the nation in wine production and has about 300 wineries. Due to its agritourism-based enterprises, the grape and wine industry has an estimated $1.4 billion impact on the Commonwealth's economy. Several Pennsylvania grape growers have reached out to Penn State Extension to report herbicide damage and to ask for guidance on how to mitigate vine damage from herbicide drift. As mentioned above, the matter is more importantly about farming coexistence, good communication among neighbors, and pesticide stewardship. Thus, while we know what factors may result in herbicide damage to grapevines, the issue of herbicide drift is complex and nuanced. It is lawful to follow the label. However, even after the herbicide has been applied, certain environmental conditions and land topography may augment the chances of herbicide damage (e.g. via vapor drift) to neighboring vineyards. In collaboration with the USDA-funded North Central IPM Center, the Herbicide Drift Risk Management Special Project Group has developed a series of extension fact sheets written for specialty crop (e.g. grapes, vegetables, etc.) growers. While some vineyards in PA have signed up for DriftWatch, it is possible that not all have registered with this program. A non-exhaustive list of wineries in PA and a county-based map of where some vineyards exist can be found online.

Note: (1) not all wineries have vineyards; (2) vineyards may exist where wineries do not; and (3) the information in these online resources is limited by stakeholder participation. Thus, for the vineyard owner, we encourage good scouting of the surrounding agricultural enterprises that use PGR herbicides (from agronomic farms to rights-of-way to commercial turf and landscape management); for the PGR herbicide applicator, we encourage referencing Drift Watch and scouting of the surrounding agricultural enterprises that produce herbicide-sensitive crops (e.g., vineyards, vegetables, etc.).

When are grapes most sensitive to herbicide drift? 

There are too many factors to consider when making definitive statements about the extent of grapevine damage that herbicide drift can cause. For example, herbicide type, herbicide rate, drift/deposition extent, weather patterns, vine age, vine growth stage, cultivar, and other factors can all affect the "damage potential" of herbicide drift or volatility. We know that grapevine tissues are sensitive to many herbicides, as noted above. We do not know the growth stages at which herbicides are the most damaging to grapevines. Observationally, however, it is likely that herbicides can cause extensive damage to grapevines between bud break and fruit set, as it is between these stages that the vine is growing tissues that will set the current, and determine forthcoming season's, crop yield potential. Further, from a concentration perspective, herbicide drift at these early season growth stages could be problematic due to the relatively small amount of vegetative tissue biomass on vines at this time of the year. Grapevine bud break generally commences in mid- to late-April throughout southeastern PA vineyards and continues through early May in vineyards located in central, northern, and western regions of PA. Grapevine bloom and fruit set generally occur from early June in southeastern PA vineyards through late June in northwestern PA vineyards. Thus, while critical grapevine growth stages occur in April through June, herbicide drift throughout the growing season (April through October) can damage grapevine tissues. A good approach is to follow the label guidelines and use best herbicide stewardship practices to avoid the chances of herbicide drift and volatility to vineyards and other sensitive specialty crop farms.

Related and Current Efforts at Penn State Extension

Penn State Extension is taking a cross-disciplinary approach to educate and conduct research focused on herbicide drift issues in vineyards. Penn State staff and faculty that have backgrounds in weed science, viticulture, agricultural economics, and law are collaborating on grants supported by the Pennsylvania Wine Marketing and Research Program Board and funded by the Pennsylvania Liquor Control Board. The objectives of the grants are to conduct herbicide drift research in grapevines, understand methods of sampling tissues for herbicide detection, survey industry stakeholders (herbicide applicators, vineyard owners) across Pennsylvania to understand more about the scope and scale of herbicide drift issues, and develop educational deliverables (e.g., workshop, media-based extension products). The team of investigators looks forward to sharing results and deliverables with industry stakeholders.

Here are two Extension articles that are products of this cross-disciplinary collaboration: 

• Field Guide to Vineyard Herbicide Drift
• A Review of Survey Results Regarding Auxin Herbicides and Vineyard Damage Grape Grower Feedback