Wine grapes are increasing in acreage and value in many parts of Texas. These crops are often surrounded by other field and pasture crops that are important to the overall agricultural economy in the state. Grapevines are very sensitive to the application of certain herbicides commonly used to control weeds in field and pasture crops. Many applicators do not realize the hazard that these herbicides present to grapevines and the production of wine products.
Damage is often caused by the use of phenoxy or hormone type herbicides containing the active ingredients 2,4-D, 2,4-DB, MCPA, MCPP, dicamba, picloram, clopyralid and triclopyr. This family of herbicides is very effective and economical for controlling broadleaf weeds. These herbicides are commonly used on a variety of sites such as lawns, golf courses, rights-of-way and agricultural fields. Some do not require a pesticide applicator license for purchase or use and are available at a variety of retail locations.
Grapevines, ornamental plants and many broadleaf crops are extremely sensitive to herbicides containing phenoxy active ingredients. These plants are sensitive to phenoxy herbicides throughout the growing season, but some crops, such as grapevines, are particularly vulnerable from the early growing season through the bloom period. This vulnerable period may vary depending on the part of the state where these crops are grown. Exposure to phenoxy herbicides during the active shoot growth period causes growth to stop temporarily and may retard growth for several weeks. If effects are not too severe, normal growth may resume the same or following year. Severely injured grapevines may not recover for two years or more. Exposure to phenoxy herbicides during bloom can greatly reduce fruit set, and injured vines may have delayed fruit ripening. Severe injury can prevent complete maturation of the fruit. The delayed maturity effect may exist for one to three years before normal ripening resumes.
Grapevines are effected when herbicide drift and/or volatilization occurs. Herbicide particles or vapors may be moved from the application site by wind, shifting air currents, climatic inversions or using high pressures when spraying. Even minute amounts of phenoxy herbicides that move from the application site can create symptoms in grapevines. Grapevines and other sensitive crops in close proximity to the application site are at most risk, but sensitive crops at greater distances from the application site may be vulnerable.
Symptoms of phenoxy herbicide exposure are most pronounced on the youngest leaves and the tips of growing shoots. Affected leaves may be small, narrow and have closely packed thick veins that lack chlorophyll. Farther down the shoot, symptoms are typically less severe and older leaves may have a distinctive fan-shaped appearance with parallel strap-like veins. Leaves may also be cupped and leaf margins often end in sharp points. Small, puckered interveinal spots may retain some green chlorophyll and affected flower clusters often set few or no berries.
The risk of phenoxy or hormone type herbicide exposure to grapevines and other sensitive crops can be reduced by taking a number of precautions when applying herbicides. These precautions include:
- Consider using an herbicide that does not contain a phenoxy-type active ingredient.
- If a phenoxy-type herbicide is used, the risk of volatilization may be decreased by using an amine (dimethylamine salt) formulation instead of an ester formulation.
- Time applications to occur in early spring before grapevines begin to grow or make applications in the fall after leaves have dropped.
- Use extreme caution when making applications whenever sensitive crops are in the vicinity and temperatures are increasing.
- Monitor wind speed and direction closely.
- Read and follow all label directions and precautions of the herbicide being applied.
- Adding a spray-thickening agent (drift retardant) may reduce particle drift.
Communication with your neighbors may be the most effective tool to mitigate the possibility of phenoxy-type herbicides applications posing adverse effects to sensitive crops. Vineyard owners should let their neighbors know of the presence or location of their vineyards and that grapevines are extremely sensitive to some herbicides. Recommend that applications be made before the vines bloom or consider using an alternative to phenoxy herbicides. Suggest to your neighbor to spray when the wind is calm or blowing away from the vineyard.
TDA investigates all reports of adverse effects occurring from the use of pesticides. Upon receipt of a report, an investigation is conducted to determine if the pesticide was used inconsistent with its label and to determine if a violation of pesticide laws or regulations occurred in connection with the reported incident. TDA takes enforcement action appropriate to address the violation documented in the investigation. Timely reporting of any occurrence of adverse effects is critical to the ability of TDA to gather information necessary to determine if a violation occurred.
If you suspect that your grapevines have been affected by herbicide drift, contact the Texas Department of Agriculture at 1-800-TELL-TDA or contact the nearest TDA Regional Office.