Modern agronomic practices include the use of more and more non-selective herbicides. RoundUp Ready® crops already are widely planted and are being supplemented with 2,4-D and dicamba resistant crops. The latter were developed in an effort to control weeds that have become resistant to glyphosate. Additionally, copious amounts of non-selective herbicides are being used to chemically “burn down” cover crops before the land they occupy is planted in the spring.
The above presents a problem for vegetable growers located adjacent to crop farmers. During herbicide application, very fine droplets or products of volatilization can find their way to areas where application was not intended and, as a result, vegetables, ornamentals, and trees can show herbicide injury symptoms. Unfortunately, reports of the latter have been on the increase in recent years.
The extent to which an herbicide will drift from its intended target depends on several factors such as the type of herbicide, environmental conditions (e.g. wind speed) at the time of application, and sensitivity of surrounding plants. Anyone familiar with tomato knows it is one of the most sensitive crops grown, and the majority of the aforementioned cases of accidental herbicide damage has involve tomato.
The most common cause of accidental herbicide contamination is particle drift, which occurs when small droplets are blown off-target by the wind. Damage from this type of drift most often is quite proximate to the herbicide application site and largely can be prevented using proper application techniques. Spots from these droplets may be quite obvious and consistent on a selection of plants in the area.
Plant damage from products of herbicide volatilization is much less common and harder to diagnose. It is also difficult to prove or consider pesticide misuse*. Damage has been known to occur miles from the application site, depending on the herbicide involved and sensitivity of plants damaged.
Vegetable growers should be aware of what crop is planted in adjacent fields and what kind of herbicide practices might be used for that crop. Since this land often is owned by other farmers, conversations with one’s neighbor is an important first step in the prevention of accidental herbicide injury. Producers of agronomic crops often are not aware of the extreme sensitivity of vegetable such as tomato to herbicides. This becomes a somewhat urgent matter as we get into the post emerge weed control chemicals for field crops such corn and soybeans.
If growers suspect accidental herbicide damage to one or more of their vegetable crops, an orderly series of steps should be taken. First, when damage occurs, the damage needs to be documented. The date should be noted and a review of damaged plants should be written down. As quickly as possible, a combination of photos and plant samples should follow. MU Extension and its Diagnostic Lab can help to document symptoms, but do not perform residue testing. Missouri Department of Agriculture can assist with taking plant samples for residue testing; this is only done when filing a formal complaint.
Next, try to determine if other causes of plant stress (e.g. temperature, fertilizer) might be mimicking herbicide injury. Off-target movement of herbicides will cause multiple plants over a large area to exhibit similar symptoms. Grows should carefully observe leaf margins, new growth and the main stem, as these areas can offer several clues for herbicide damage. The University of Tennessee has developed a helpful publication showing the response of tomato to a number of different herbicides, including those used on forages. The publication can be found at: https://ag.tennessee.edu/herbicidestewardship/Pages/Tomato%20and%20Pasture%20Herbicides.aspx.
If herbicide injury is suspected, growers should attempt to narrow down the source of contamination. After ruling out one’s own negligence (e.g. use of an herbicide-contaminated sprayer to apply other pesticides) attention should be turned to “off farm” sources. If damage is most severe in plants adjacent to a field recently sprayed by a neighbor, there is fairly strong evidence that the neighbor’s action caused the injury. Also, looking for patterns in a planting can help determine the source of contamination. A change in the intensity of symptoms in a field may indicate the direction which the herbicide came.
Unfortunately, herbicide injury cannot be reversed. Even though plants may somewhat recover, yields will be lower which can result in significant economic loss. If there is strong evidence that the action of a neighbor or chemical applicator hired by a neighbor is the cause of herbicide damage to a crop, then normal “economic loss resolution” procedures should be followed.
There are several approaches one can follow for seeking either compensation or, at least, the recognition of the problem. The approach chosen likely will be determined by the severity of the damage, the relationship with the individual who caused the damage, their willingness to acknowledge it, or some combination of these.
These approaches include:
Contact the Missouri Department of Agriculture (MDA) and report the incident. This should be done as quickly as possible following the incident by telephone (573-751-5504). An investigation by the MDA will result. Click here for complete MDA information on procedures for investigating possible pesticide misuse and submitting a pesticide incident report. If the MDA is contacted, an investigator will visit the farm to ask questions and conduct the investigation; there are eight spread across the state. At that time, the grower will have the opportunity to:
Ask that formal action is taken. The inspector will then spend time collecting samples. To follow the proper process, this may take several hours. The inspector will advise the grower on a number of issues. A few of special interest include:
Decline any formal action. This needs to be done within the first 10-20 minutes of the inspector visit. The declining of formal action often occurs as the inspector verbally reviews what was just presented above.
The preceding does appear to be a lot of trouble, especially in the midst of a busy production season. If herbicide damage is fairly minimal, the question arises if one should even pursue it. A convincing reason to follow up on even mild damage is to try and prevent accidental herbicide damage from occurring in the future. Even good neighbors are not likely to change their farming practices if they do not know anything “bad” happened because of their actions. Notifying the farmers involved when incidents of accidental herbicide contamination occur is the best way to motivate them to be better neighbors to vegetable growers.
*Pesticide misuse can be the result of several actions, such as pesticide drift, personal protection equipment violations, site violations, rate violations, etc.
The authors would like to express appreciation to Darryl Slade (Enforcement Program Coordinator for the Bureau of Pesticide Control of the Missouri Department of Agriculture) for his assistance.
REVISED: May 23, 2016