Grape production is an increasingly important component of agriculture in Tennessee and many parts of the United States. Since many vineyards are located near pastures, hay fields or roads, off-target movement of pasture and right-of-way herbicides is becoming a major issue in grape production. While these herbicides are valuable tools for weed management, off-target damage to grape often results in expensive fines and/or lawsuits, reduced yields, delayed ripening, and poor fruit quality. Fortunately, preventive steps can be taken to avoid these problems.
Preventing Herbicide Injury in Vineyards
(For more information, please refer to Extension publication Preventing Off-target Herbicide Problems in Vineyards, W297-A)
Agricultural chemicals, particularly pasture and right-of-way herbicides, have the potential to cause off-target damage to grapes. Although these herbicides control many troublesome weeds, off-target damage to tomatoes often results in expensive fines and/or lawsuits, lost productivity for growers, and even crop rejection. Several management practices can be adopted to avoid these problems.
- Herbicide Selection -- Although highly effective on several broadleaf weeds in pastures and rights-of-way, the auxin or growth regulator herbicides can damage sensitive crops if not used properly. The characteristics of these herbicides determine which product to use in different situations.
- Volatile herbicides -- change from a liquid to gas or vapor and
move away from the target. Typically, dicamba and 2,4-D are more
volatile than aminopyralid or picloram.
- Persistence of herbicides -- The persistence of herbicides can
affect future plans for a field. While dicamba and 2,4-D are highly
active on grapes even in minute doses, these materials are relatively
non-persistent in soil and in treated pasture grasses and hay. This is
not the case with aminopyralid or picloram. Both of these herbicides can
stay active in soil, pasture grass and hay for a year or longer
- Water Solubility -- Picloram is more soluble than aminopyralid and therefore more likely to be moved off-site by runoff.
- Prevention of Drift -- Several factors can contribute to herbicide drift to sensitive areas. physical and vapor, can occur. (Refer to the section "Spray Today?" in this website)
- Physical Drift -- can occur when the herbicide is blown away
from the target area on windy days and/or in runoff after a hard rain.
It is important to monitor weather conditions several days prior to and
after spraying to prevent physical drift.
- Vapor Drift -- is the movement of spray vapor away from the target
after the herbicide has been deposited on the target. It is mainly
influenced by air temperature, but also by relative humidity (RH) and
herbicide formulation.
- Field Selection -- The location, characteristics and history of a field influence future management strategies. A proper risk assessment should be performed before spraying a pasture with some of these herbicides. Rains can wash certain herbicides downhill to sensitive areas.
- Sprayer Contamination -- A common way for pasture herbicides to make it into vineyards is through sprayer contamination. Pasture herbicides are notoriously difficult to rinse from sprayers. Rinsing with water does not remove all herbicide residues from a sprayer and hoses
- Monitoring -- Producers are encouraged to assess the performance of herbicides in
pastures and hay fields. Tracking results will guide future decisions
for weed control. It is important to keep a log of all applications with
dates, products, field locations and weather conditions.
Diagnosing Suspected Herbicide Damage to Grape Vines
Following proper stewardship recommendations can reduce the impact of off-target herbicides in vineyards (see UT Extension fact sheet W 297-A Preventing Off-target Herbicide Problems in Vineyards). However, these unfortunate events sometimes occur and diagnosing problems in the field is difficult. Many pasture herbicides mimic the plant hormone auxin, and symptoms can be quite similar.
Images and descriptions on this webpage are intended to highlight characteristic symptomology of each of these broadleaf herbicides on grape vines.
The following are descriptions of commonly observed symptoms resulting from exposureto synthetic auxin herbicides:
- Curling — Folding of edge of leaf margins.
- Epinasty — Twisting, bending and/or elongation of stems and leaf petioles.
- Blistering — Appearance of raised surfaces on leaf tissue.
- Chlorosis — Yellowing or whitening of leaves resulting from loss of chlorophyll.
- Necrosis — Browning of tissue resulting from cell death.
Grapevine exhibits curling, epinasty and chlorosis
Herbicides Evaluated for Symptomology in Grape Vines
Common Name:
Chemical Family:
Trade Names:
aminocyclopyrachlor*
Pyrimidine-carboxylic acid
Not registered for use in pastures and hay fields
aminopyralid
Pyridine-carboxylic acid
Milestone, ForeFront R&P, ForeFront HL, GrazonNext
picloram
Pyridine-carboxylic acid
Tordon, Surmount, GrazonP+D
2,4-D**
Phenoxyacetic acid
Various names and mixtures
Dicamba
Benzoic acid
Banvel, Clarity, Oracle, Rifle, Brash, Rangestar, Weedmaster
*Products containing aminocyclopyrachlor (MAT28) are registered for non-cropland use, but are not yet registered for use in pastures.
**Picloram, aminopyralid, and dicamba are often sprayed in combination with 2,4-D.
Picloram Injury Symptoms
After exposure to picloram, grape vines exhibit symptoms relatively soon.
- Within four days after exposure, new leaves start folding upward (Figure 1).
- At one week, young leaves continue to curl and leaf petioles and stems begin to droop (Figure 2). Plants are generally not as upright as those exposed to aminocyclopyrachlor or aminopyralid.
- Higher rates of picloram exposure lead to severe drooping and early signs of necrosis within two weeks after exposure (Figure 3). Large leaves are often folded in half lengthwise and new growth has nearly ceased.
- At lower rates of picloram exposure, drooping is not as severe, and new leaves are cupped upward at two weeks (Figure 4).
- Within three weeks, higher rates of picloram exposure will result in plant death (Figure 5).
- Within three weeks, lower rates of exposure will result in yellowing of younger leaves and down-cupping of older leaves (Figure 6).
The following plant images were photographed over time to illustrate the development of symptoms after plants were exposed to picloram.
Aminocyclopyrachlor Injury Symptoms
After exposure to aminocyclopyrachlor, grape plants exhibit symptoms relatively soon.
- Within four days after treatment, petioles are drooping and new leaves are folded upward (Figure 7).
- At one week, petiole epinasty has become more severe (Figure 8). Also, young leaves are slightly puckered and rippled, and are beginning to lose color.
- Within two weeks, older leaves are cupped downward and some have started to turn brown (Figure 9). New leaves are folded upward and curled around the margins (Figure 10).
- At three weeks, lower rates of aminocyclopyrachlor exposure have resulted in more petiole bending and interveinal chlorosis in leaves (Figure 11).
- At three weeks, higher rates of exposure have caused severe yellowing and more pronounced puckering and rippling in young leaves (Figure 12).
The following plant images were photographed over time to illustrate the development of symptoms after plants were exposed to aminocyclopyrachlor.
Aminopyralid Injury Symptoms
Symptoms typically develop slower with aminopyralid than with picloram or aminocyclopyrachlor.
- New leaves and petioles are starting to curl within four days after
exposure (Figure 13).
- Within one week, young leaves begin to develop into a distinct cup shape, and stems are elongated (Figure 14). Soon after, the cup shape is more extreme in youngest leaves, and all leaves show signs of chlorosis (Figure 15). Slightly older leaves are curled around margins and rippled near the veins (Figure 16).
- Within three weeks, older leaves have become more yellowed and cupped downward, but petioles are only slightly epinastic (Figure 17).
- In young leaves, cupping and rippling symptoms remain and new growth has slowed (Figure 18).
The following plant images were photographed over time to illustrate the development of symptoms after plants were exposed to aminopyralid.
2,4-D Injury Symptoms
Symptoms begin to appear more quickly with 2,4-D than with aminocyclopyrachlor or aminopyralid.
- Within four days after exposure, young leaves are folded in half lengthwise and petioles are drooping (Figure 19).
- At one week, older leaves have cupped downward and petioles continue to twist and bend (Figure 20).
- With higher rates of exposure to aminopyralid, plants exhibit necrotic symptoms within two weeks (Figure 21).
- With lower rates of exposure, new leaves have become fan shaped and are toothed from reduced lateral expansion (Figure 22).
- At three weeks, young leaves are fan-shaped, strappy and have sharp points around the leaf margins (Figure 23).
- After three weeks, most leaves are losing color, and stems also may have a zigzag shape and shortened internodes (Figure 24).
The following plant images were photographed over time to illustrate the development of symptoms after plants were exposed to dicamba.
Dicamba Injury Symptoms
Overall, symptoms develop quickly in plants exposed to dicamba.
- Petioles are drooping and young leaves are folded four days after exposure (Figure 25).
- At one week, petioles have bent down farther, and some of the older leaves are folded (Figure 26).
- Yellowing and browning of leaves are apparent by two weeks with high rates of exposure to dicamba (Figure 27).
- With low rates of exposure, new leaves are cupped upward and puckered and are similar to aminopyralid symptoms (Figure 28).
- Approximately three weeks after higher rates of exposure, all petioles are epinastic, leaves are yellowed, and new growth has ceased (Figure 29).
- After three weeks with lower rates of exposure, older leaves are folded down and new leaves are severely cupped (Figure 30).
The following plant images were photographed over time to illustrate the development of symptoms after plants were exposed to dicamba.
Guidelines and Recommendations
Although diagnosing herbicide injury in the field is difficult, the following steps can be taken to determine possible causes:
- Always record the date, time, location and description
of observed symptoms.
- Photographs of injury can help document symptom development, especially since the appearance of plants can change over a short period of time.
- Try to rule out other causes of plant stress, such as weather, soils, insects or misapplied fertilizer.
- Be aware that 0ff-target movement of herbicides will cause multiple plants over a large area
to exhibit similar symptoms.
- Pay particular attention to leaf margins, new growth, and the main stem, as these areas can offer several clues for herbicide damage.
- If herbicide injury is suspected, it can be difficult to determine if the herbicide was placed there by:
- tank-contamination,
- drift,
- moved after the application of a herbicide due to volatility,
- possibly placed there by manure or urine from livestock who fed on treated forage.
- Research is important to narrow down the source of contamination.
- determine when symptoms first appeared
- whether livestock were given access to the field in the off-season,
- what the previous crop was and what
herbicides were applied in the previous three seasons,
- whether manure was used,
- if there was an application of pesticides soon before the symptoms appeared.
- Looking for patterns in fields can also narrow down the source of contamination.
- Scattered patches of herbicide damage may indicate carryover in manure and urine.
- If the majority of plants are injured, then a change in the intensity of symptoms in the field may indicate from which direction the herbicide came.
- Vapor drift can travel several miles, though, making the direction of origin difficult to determine.
- Herbicide residue testing is expensive, especially if the herbicide or family of herbicides is unknown. Being able to narrow the list of possible herbicides can significantly lower the cost of residue testing.
- One important thing to remember is that picloram, aminopyralid and dicamba are often sprayed in combination with 2,4-D. Even though pasture herbicides damage grapevines in similar ways, the descriptions listed on this webpage can help to verify the source of injury.