Growth Regulator Herbicides and Grapes Don’t Mix
By: Andy Muza, Penn State Extension – Erie County
All herbicides registered for grapes have the potential to cause herbicide injury in vineyards if not applied according to the pesticide label. Over the years, I have observed phytotoxicity in vineyards due to improper applications of simazine (Princep), diuron (Karmex), paraquat (Gramoxone) and most notably, glyphosate products (Roundup, Touchdown, etc.). However, of much greater concern for growers are certain herbicides not registered for grapes which are applied to unwanted vegetation in other crops/non-crop areas in proximity to vineyards.
Herbicides are grouped, by the Herbicide Resistance Action Committee and the Weed Science Society of America, according to their Mode of Action. Within these groups, herbicides are further classified according to their Chemical Family.
Grapes are extremely sensitive to very low concentrations of herbicides containing 2,4-D. 2,4-D is classified in the Family of phenoxy–carboxylic–acids which are within the Growth Regulator mode of action group. In addition to 2,4-D other Growth Regulator (GR) herbicides which have been documented as causing injury to grapes include dicamba (Banvel, Clarity, etc.), picloram (Tordon) and triclopyr (Garlon). However, all of the GR herbicides should be considered to have the potential to cause injury to grapes. Therefore, their use around vineyards should be discouraged. GR herbicides are commonly applied to lawns, turf, pasture, agronomic crops (e.g., corn, cereals, sorghum) and noncropland (e.g., roadsides, right of ways). There is a wide variety of GR herbicides and for a partial listing of product trade names refer to References 1 and 2 below. Also, be aware that many prepackaged mixes may contain a GR herbicide.
How Growth Regulator Herbicides Work
Auxins are plant hormones which regulate growth and development in the plant and are in the highest concentrations in the growing tips. Growth regulator (GR) herbicides mimic these plant hormones. These herbicides are systemic and translocate from absorption sites (leaves or roots) to areas of rapid growth. Abnormal growth results due to disruption in the hormonal balance of the plant. The youngest terminal growth is most severely affected.
The most severe cases of injury to grapevines, that I have seen, have been caused by herbicides which contain 2,4-D. There are numerous products on the market with various trade names and these are available for both homeowner and commercial use. Grape is considered one of the crops most susceptible to injury. Although all grape varieties are susceptible to 2,4-D injury there are differences among cultivars (refer to Reference 3 below).
Drift – is defined as the movement of a pesticide from the intended application site to an unintended site (i.e., off target movement). Spray drift results when fine spray droplets move in wind currents to non-target areas. Vapor drift occurs when spray material evaporates from the application site and vapors are moved to off target areas. Vapor may be generated under high temperatures during and after application.
2,4–D Formulations – products are formulated as both esters and amines. Most ester formulations available today are much less volatile than previous products. However, there is still a greater risk of vapor drift with ester formulations than with amine formulations. Amine salt formulations are safer to use, especially at temperatures greater than 80 degrees Fahrenheit.
2,4–D Injury – has been reported to occur 5 miles or more downwind of where herbicide applications were applied. However, the most extensively injured vineyards are usually within closer proximity of the herbicide application. The severity of injury depends on: the amount of herbicide absorbed by the vines; growth stage of the vines at time of exposure; age of vines; and variety. Vines exhibit the most extensive injury if exposed to 2,4–D earlier in the season, during the period of rapid shoot growth (bud break through bloom). Young vines are more likely to be killed that older vines. Depending on the severity of the injury vines may not recover for 2 years or more.
Shoots – shoot tips may stop growing or exhibit twisted growth with deformed leaves.
Leaves – a variety of leaf distortions may occur such as: small, narrow leaves with numerous, thick white veins and pointy leaf margins; fan shaped, puckered leaves with pointed leaf margins.
Clusters – injury to clusters can include: flower abortion; fruit set reduction; reduction of fruit size (shot berries intermingled with normal size berries); delayed ripening; and reduction in fruit quality.
Proactive Approach to Minimize Problems
It is always easier (and less costly) to take steps to prevent injury than to deal with the problem after the fact. Homeowners, other farmers and commercial applicators (e.g., lawn care companies and county/state highway departments) are often not aware that commonly used GR herbicides can cause serious injury to grapevines. Therefore, grape growers should inform them about their vineyard locations. The Applicator Practices and References listed below can be used to educate neighbors and commercial applicators about the hazards of using Growth Regulator herbicides near vineyards.
Applicator Practices to Reduce Risk of Growth Regulator Herbicide Injury
- Be aware of vineyards in close proximity of herbicide applications.
- Read the herbicide label and follow precautions concerning spray drift.
- Avoid application of growth regulator herbicides near vineyards from bud break through fruit set.
- Use less volatile Amine formulations of GR herbicides.
- Monitor weather conditions (wind speed and direction, temperature). Avoid spraying when wind speed is likely to cause spray droplets to drift. Spray when wind direction is moving away from vineyard. Avoid applications if a temperature inversion exists. Remember, high temperatures during and a few days after application increase the risk of vapor drift.
- Use nozzles (e.g., air induction nozzles) that reduce drift by increasing droplet size.
- Keep spray pressure at lower end of pressure range and boom height as close as possible to target.
- Consider using a drift reducing additive.
- Preventing Herbicide Drift and Injury to Grapes https://catalog.extension.oregonstate.edu/files/project/pdf/em8860.pdf
- Preventing Hormonal -Type Herbicide Damage to Kansas Grapes http://www.agmrc.org/media/cms/s142_a7a8702475b22.pdf
- Questions and Answers about Vineyard Injury from Herbicide Drift http://www.bookstore.ksre.ksu.edu/Item.aspx?catId=237&pubId=1105