Note: This fact sheet is written as an informational bulletin that can be distributed to commercial pesticide applicators and to farms and homesteads in the vicinity of vineyards. Print Version - pdf
Avoid Phenoxy Herbicide Damage to Grapevines
Ed Hellman
Texas Cooperative Extension
What are phenoxy
herbicides?
Perhaps as many as one hundred or more herbicide formulations contain a phenoxy-type active ingredient. Some of the more commonly used phenoxy products include 2,4-D, MCPA, Weedone, Weedmaster, Crossbow, Banvel, Garlon, Grazon, Weed-B-Gone, and Brush Killer. The active ingredient of phenoxy-type herbicides may be listed on the label as 2,4-dichlorophenoxy-acetic acid, 2-methyl-4-chlorophenoxyacetic acid, triclopyr, or dicamba.
This family of herbicides is very effective and provides relatively inexpensive broadleaf weed control for lawns, golf courses, and right-of-ways. Phenoxy herbicides are also an important tool for broadleaf weed control in pastures and for production of peanuts, corn, sorghum, wheat and other small grain crops. Common target weeds for these herbicides are pigweed, morningglory, cocklebur, nightshade, and other broadleaf weeds.
These products come in containers ranging from 1-quart bottles
of ready-to-use solution to 5-gallon drums of highly concentrated active
ingredient. They do not require a pesticide license for purchase and are
readily available from department stores, home improvement stores,
co-ops, garden centers, retail nurseries, and farm chemical dealers.
Grapevines are highly
sensitive
Grapevines are extremely sensitive to
herbicides containing phenoxy-type active ingredients. Sensitivity to phenoxy herbicides exists throughout the grapevine's growing season, but
they are most vulnerable from the early growing season through the
bloom and fruit set period (early April through early June).
During the active shoot growth period, phenoxy damage often
causes growth to stop temporarily and to be retarded for several weeks.
If the effects are not too severe, normal growth will resume the same or
following year. Growth may stop completely on severely injured shoots and heavily damaged vines may not recover for 2 years or
more.
Flower clusters are particularly sensitive; exposure during
bloom can greatly reduce fruit set. Injured vines also may have delayed
fruit ripening. Severe injury can prevent complete maturation of the
fruit. The delayed maturation effect may exist in a vine for 1 to 3
years before normal ripening resumes. Slight injury may have little or
no effect upon fruit maturity.
Texas vineyards have experienced significant crop loss and
long-term damage to vines inadvertently exposed to phenoxy herbicides
applied to distant targets. In contrast, minor symptoms on grape leaves
probably do not cause crop loss, but it can take significant time and
energy to resolve the issue with a neighbor.
How damage occurs
Unintended off-target drift of herbicides can be caused by wind, shifting
air currents, climatic inversions, or spraying at high pressure (which
causes a very fine mist). Aerial applications can be especially subject to off-target drift and reports have been made of drift damage from phenoxy herbicides up to 40 miles or more from the area of application (Frazier, et al., 1970). Grapevines will exhibit damage symptoms when exposed to only minute amounts carried by the wind.
Grapevines in close
proximity to a sprayed area are at highest risk. However, even
grapevines some distance from a phenoxy-treated area can be damaged
under certain conditions. Even slight winds can carry small spray
droplets toward a vineyard. Temperatures above 70-75°F allow phenoxy herbicides, especially ester
formulations, to volatilize (vaporize) and be
carried by the wind, even several days after the spray
application.
Symptoms of phenoxy
injury
The symptoms of phenoxy herbicide damage are most dramatic on
the youngest leaves and the tips of growing shoots (Figures 1 and 2).
Affected leaves are small, narrow, and misshapen, and have closely
packed, thick veins that lack chlorophyll. Farther down the shoot,
damage symptoms are progressively less severe; leaves have a distinctive
fan-shape appearance with parallel, strap-like, clear veins (Figure 2).
The leaves sometimes are cupped, and the leaf margins often terminate in
sharp points. Small, puckered, interveinal spots retain some green
chlorophyll. Damaged flower clusters set very few or no
berries.
 |
 |
| Figure 1.--New leaves and growing tips
show the most severe damage. Affected leaves are small, narrow,
and misshapen. |
Figure 2.--Farther down the shoot,
leaves have a fan-shape appearance. Leaves sometimes are cupped,
and margins often end in sharp points. |
Reducing the risk of phenoxy
damage
The most effective means of reducing the risk to your vineyard is to talk with your neighbors and commercial pesticide applicators in the area. Use this fact sheet to inform them of the high risk of damage to grapevines posed by phenoxy herbicide use. Encourage them to use herbicides with a different active ingredient. If they still prefer a phenoxy herbicide, suggest that they use an amine (dimethylamine salt) formulation
instead of an ester formulation, which will decrease the risk of
volatilization. Ask them to consider making applications in early
spring (prior to March 15) before grapevines begin to grow or in the fall after their leaves
have dropped.
Off-target drift can be minimized by careful application timing and methods. Wind speed and direction should be monitored closely and applications postponed until drift potential is very low. All label
directions, restrictions and precautions should be read before using any pesticide. Spray-thickening agents (drift retardant) may help to reduce spray drift.
Finally, encourage a good neighbor relationship that will enable all parties involved to effectively conduct their operations.
References
Frazier, N.W., J.P. Fulton, J.M. Thresh, R.H. Converse, E.H. Varney, and W.B. Hewitt (eds.) 1970. Virus Diseases of Small Fruits and Grapevines. University of California Division of Agricultural Sciences, Berkeley, California. pp. 247-250.
