Grape leaves exhibiting phenoxy-type herbicide damage in 2017. Photo: T. Delvalle, Penn State
Herbicide drift. It is probably not the first time you have heard of it, and it won’t likely be the last. But I can assure you, that if you cause a substantial amount of drift-related damage, you may be getting a call from the Department of Agriculture, or potentially even a lawyer. It is likely that you wouldn’t even know that you caused the damage until someone knocks on your door. The most important thing to remember is that you (the applicator) are responsible for pesticide drift, even if environmental conditions are the cause. And despite what you may think, it does not take much chemical to cause damage onto a nearby crop. For example, grapes can be damaged by 2,4-D at up to 100 times less than the labeled rate for controlling weeds!
Herbicide drift onto vegetable and fruit crops unfortunately occurs regularly across Pennsylvania, especially in the spring. Why? Because spring is the time of year herbicides are applied to various crops to kill newly emerged weeds; both on farms and in lawns. This also coincides with the time of year that certain crops (i.e. grapes and tomatoes) are most susceptible to herbicide damage.
Drift can occur in two ways; particle drift or vapor drift. When small spray droplets move long distances due to wind, it is called particle drift. To minimize particle drift, it is recommended to use air induction nozzles, and/or low pressure nozzles, in addition to spraying in low winds. Vapor drift is when a pesticide volatilizes or evaporates into the atmosphere and moves off site and damages non-target plants. It is suggested to use amines instead of esters in warm temperatures for this reason.
Field crops are not the only place where drift comes from. Documented drift has come from many sources; including vegetable fields, lawn care applications, right of way and industrial areas, forest weed control applications, aquatic weed applications, and even homeowner-related lawn and garden applications. Certain plants are more susceptible to herbicide drift. These include (but are not limited to) grapes, tomatoes, fruit trees, watermelons, tobacco, sweet potatoes, and certain ornamentals. In fact, some plants are up to 20 times more sensitive to 2,4-D or other auxin-related herbicides than to glyphosate.
When drift occurs, depending on the crop, damage may take several weeks to show up. Additionally, a single case of drift can effect plant growth and harvests for several years. For example, a single instance of 2,4-D drift onto a grape plant can minimize or prevent a harvest for two or three years. An applicator may be summoned to court for lost income if this happens (and it does).
The following herbicides are typically associated with increased risk for drift-related damage to non-target crops: 2,4-D, MCPA, MCPP, triclopyr, dicamba, picloram, clopyralid, aminopyralid, and quinclorac. Whether you are a crop grower, a lawn care professional, or right of way professional, you have likely used or continue to use products that contain one or more of these ingredients.
Remember that drift—especially vapor drift—can travel in excess of one mile, especially when ester products are used in warm temperatures (drift is not always caused by high winds). Be sure to read the label, and use common sense. Take note of air temperature and the formulation you are using, look at the wind speed and wind direction, and finally, understand what type of crops are nearby, especially downwind of your intended application. If there is a vineyard nearby, you should pay close attention to your product choice and environmental conditions. Speak with your local farmers, and develop a relationship with them. By taking the initiative to go through these steps, you could save yourself or company from fines, or potentially even a lawsuit.
Grape cluster showing phenoxy-herbicide damage in 2017. Every plant on several acres exhibited this symptom. You can imagine how poor the harvest will be this year, and probably next year as well. Photo: T. Delvalle, Penn State