Cause Several classes of herbicides and pesticides can cause damage to grapevines. Some of the most damaging chemicals are 2,4-D herbicides. Grapes are very sensitive and frequently are damaged by chemical drift from nearby applications. Grapes are most sensitive from bud break through bloom but can become damaged anytime during the growing season. The ester form, commercially available as Crossbow, Brush Killer, and other trade names, is more volatile than the amine form. Common uses of 2,4-D esters are blackberry and brush control and broadleaf weed control in grass seed fields. On warm days, the herbicide can volatilize from sprayed areas and move several miles downwind.
Other herbicides that are damaging include Dicamba, Glyphosate, Sulfonylurea, Imidazolinone and others. The most damaging time for herbicide drift is from budbreak to fruit set. Significant exposure to these herbicides can cause fruit deformation and potential crop loss, depending on the timing and intensity of the herbicide drift.
Sulfur products used for powdery mildew control can burn foliage when applied above 85°F. The temperature relationship is correlated with increases in the daily maximum, within a few days after application. Grapes in California can withstand sulfur applications (at lower rates) above 85°F if there are no major short-term changes in the daily maximum. Once vines are acclimated to higher temperatures the chance of burn is greatly reduced. Some grapes, such as labrusca types like 'Concord' and interspecific hybrids, are genetically sensitive to sulfur even at low temperatures. Application of horticultural oils too close to sulfur applications can also damage grape leaves.
Symptoms Leaves affected by 2,4-D herbicides have a distinctive fan-shape appearance with parallel, strap-like veins. These veins are clear and terminate in sharp points at the leaf margin. (Kind of reminds some folks of chicken feet.) Small, puckered, interveinal spots retain some green chlorophyll. In severe cases, clusters shrivel up. Can take up to 3 years to recover.
Sulfur burn appears first as a bleaching between the veins. These turn brown, necrotic and dry out becoming brittle. Defoliation may occur. Injured fruit can develop brown to black scar tissue.
Injury from glyphosate may appear as a proliferation of small shoots and needle-like leaves from a single bud that persist all season.
Cultural control
- Talk to neighbors within a half-mile radius of the vineyard and advise them about the sensitivity of grapevines to herbicide drift. If possible, encourage them not to use the more volatile forms of 2,4-D. Be aware of potential drift from highway department sprays or those that may occur at parks or substations.
- Use lower rates of sulfur when the daily maximum is expected to increase significantly within the next few days. Make applications during the cooler, early morning hours.
Reference Ball, D.A., Corp, M., and Dami, I. 2014. Preventing Herbicide Drift and Injury to Grapes. OSU Extension publication EM 8860-E.