Feb 15, 2016

Managing herbicide drift becomes increasing challenge

Doug Doohan wants vegetable growers to be aware of the impacts of herbicide drift on their crops and of the production practices of neighboring farm operations.

Doohan is professor and state specialist in the Department of Horticulture & Crop Science, The Ohio State University. Located at the Ohio Agricultural Research and Development Center (OARDC) in Wooster, Ohio, Doohan spoke during the recent Great Lakes Fruit, Vegetable and Farm Market EXPO.

Herbicide drift is a fact of life for agriculture producers, Doohan said.

“A Sherman tank will drift when dropped from a plane with enough wind,” he said.

Doohan said the release of 2,4-D and dicamba tolerant corn, soybean and cotton is imminent, beginning with 2,4-D tolerant corn.

“Grain farmers will embrace these crops because they provide a new method to kill a growing range of glyphosateresistant weeds,” Doohan said. “Even modest adoption of this technology on 30 percent of the corn and soybean acreage in the Midwest will result in an increase in potential 2,4-D and dicamba use to six times the current usage.” Because these crops will cause a shift in where 2,4-D and dicamba are primarily used, from western rangeland and wheat production to the corn belt, the actual increased usage in the Midwest could be much more than a six-times increase, he said.

“Even with advanced drift reduction technology in place, the increased use of these herbicides adjacent to sensitive crops will be such that crop injury resulting from off-site movement is inevitable and almost certainly will exceed current levels (estimated at 300 incidents/ year in Ohio),” Doohan said.

Should fruit and vegetable producers in the Michigan be concerned? Doohan said the short answer is yes, as use of these synthetic plant hormone herbicides is likely to increase throughout the Midwest.

In recent decades 2,4-D and dicamba have been used for control of broadleaf weeds in cereal crops and are commonly used in lawn care and for railroad, utility right-of-way and highway maintenance purposes. 2,4-D was introduced in the 1950’s and dicamba was first registered for use in the United States in 1967.

“Unfortunately, some older 2,4-D and dicamba formulations were both notoriously prone to spray drift and to post-application volatilization,” Doohan said.

Survey results of state pesticide control officials (2005 AAPCO Pesticide Drift Enforcement Survey) listed 2,4-D as the herbicide most often involved in crop injury resulting from drift incidents for every year the survey has been taken. The same survey listed dicamba as the third most commonly involved in drift incidents for two years in a row.

“This level of crop damage from drift occurrence far outpaces the relative use of these herbicides,” Doohan said. “2,4-D ranked 7th on an EPA list of most commonly applied conventional pesticide active ingredients. Dicamba did not even make the list of the top 25.”

Doohan said these active ingredients are “highly toxic” to sensitive plants at low concentrations hence drift damage symptoms develop readily, are easy to see and are characteristic of growth regulator herbicides.

“As a result of extensive research, the causes and fixes of spray drift are well known and documented,” he said. “For example, using nozzles and pressures that result in the creation of fine spray droplets, and/or spraying during windy conditions are known to greatly increase the risk of spray drift. Much of this information is contained on the pesticide label. The instructions on the pesticide label are given to ensure the safe and effective use of pesticides with minimal risk to the environment.”

He said many drift complaints result from application procedures that violate the label. The potential for a pesticide to volatilize is related to the vapor pressure of the chemicals involved. Pesticides with high vapor pressure are likely to be more volatile than those with low vapor pressure. Pesticides known to have the potential to vaporize carry label statements than warn users of this fact.

“While there are things that the applicator can control (e.g., nozzle tip, pressure, boom height) to reduce spray droplet or dust drift, vapor drift is dependent upon the weather conditions at the time of application since the likelihood of pesticide volatilization increases as temperature and wind speed increases and if relative humidity is low,” Doohan said.

Dow AgroSciences and Monsanto, the developers of 2,4-D-tolerant and dicamba-tolerant cropping systems, respectively, have both taken great care to minimize the known negative attributes of the older 2,4-D and dicamba formulations, Doohan said.

Dow AgroSciences has developed Enlist Duo that includes a new ultra low-volatility formulation of 2,4-D with minimized drift potential, lower odor, and better handling characteristics than currently available 2,4-D amine or ester formulations, Doohan told growers.

It should be noted the EPA announced in November 2015 it plans to withdraw its approval of Enlist Duo, saying it has new information that suggests the weedkiller is more toxic to surrounding plants than previously thought.
The EPA asked the Ninth U.S. Circuit Court of Appeals to vacate the agency’s approval of Enlist Duo, which is designed to be used on genetically engineered crops, so that it may reevaluate the spray.

Dow Chemical is contesting EPA’s findings. The company expects its Enlist Duo herbicide to be available for the 2016 U.S. growing season, and continues to prepare for commercial sales of the spray.

Doohan said Dow has embarked on an educational and outreach program to farmers, dealers and commercial applicators (Enlist Ahead) to promote and encourage good stewardship of the new system.

An herbicide premix of dicamba and glyphosate branded Roundup Xtend with VaporGrip technology will be introduced upon regulatory approval of the Roundup Ready Xtend Crop System, Doohan said.

Reducing drift’s risk

“Despite everyone’s best intentions and efforts drift happens,” Doohan said. “To reduce the risk of angry exchanges with neighbors and resultant hostility we suggest an ongoing dialogue with neighbors who grow corn and soybean and with commercial spray applicators who are likely to use 2,4-D and dicamba.”
Doohan said it’s important to “create awareness. Help these individuals better understand specialty crop production and the impact of it on the state’s economy. Promote awareness among agronomic crop producers that vineyards, extensive landscape plantings, or other susceptible crops are located in their neighborhood.

“Creating and maintaining a heightened awareness of the industry is probably the most important thing we can do to reduce risk of future herbicide damage and the lawsuits that would inevitably follow,” Doohan said. “We believe that the following steps may be useful in order to help the specialty crop industry develop a process for creating and maintaining awareness and reducing the risk of drift damage.

Step 1. Inform your neighbors. Develop and maintain a good relationship with your neighbors who grow grain and forages. A good relationship starts with open communication. Offer a tour of your operation; explain how damaging drift of glyphosate, 2,4-D and dicamba can be to your crops. In the case of vineyards make sure to point out the potential for yield loss, poor grape quality, increased susceptibility to cold injury, and reduction in long-term profitability. Discuss the possibility of planting buffer vegetation between your crops and your neighbors’ crop/s to reduce risk.

Step 2. Have your farm or vineyard included in an online database. Neighboring farmers and commercial spray applicators will need accurate information on where specialty crops are being grown. Michigan growers and those from several other states can register fields and greenhouses with FieldWatch.

Unfortunately, not all states and provinces participate in the program, Doohan said.

For Ohio growers, register with the Ohio Sensitive Crop Registry. Applicators can check this website for proximity of sensitive crops to fields they are planning to spray. If you farm near roadways or other rights-of-way contact your county or state highway department, power company, etc., since hormone-type herbicides may be used for weed control in those situations.

Step 3. Manage drift of the herbicides used on your own farm or vineyard. Set an example of pesticide stewardship. Grapes are one of the most intensively sprayed crops grown in the United States. Consider the unspoken message you send to the community every time you apply pesticides; especially when using high pressure/high volume equipment.

While many herbicides are registered for vineyard use, most have severe restrictions due to the sensitivity of the crop.

“As mentioned previously, we investigate a lot of complaints and in some cases the herbicide injury problem is caused by an application in the vineyard (or vegetable field),” Doohan said.

The likelihood of drift is a multiple of many factors, but some important ones are wind speed, droplet size (determined primarily by nozzle type), the height of the nozzle above the ground or canopy and the operating pressure.

“Drift can be minimized by spraying on a morning or evening with low but not zero wind conditions (3-10 mph), keeping the nozzle close to the ground, reducing pressure (less than 30 psi), and using low drift nozzles that generate large droplets,” Doohan said.

What if drift damage occurs or is suspected? Know the symptoms of 2,4-D and dicamba injury on your crops and plan on scouting regularly during the time when grain growers are spraying.

“Early symptom detection (within a few days of drift) is important if you hope to detect residues of the causal agent – a data point that may be of great value in obtaining compensation,” Doohan said.

“Prevention is better than cure,” he said. “We encourage open and frank communication between all parties. Spell out the risk. Inform your neighbors about the high dollar value per acre of the crops you grow. Specialty crops (especially grapes) are relatively small in acreage but high in value, and are highly sensitive to trace amounts of 2,4-D and dicamba. Many are perennial crops and the consequences of drift damage can be dire and long-lasting.”

— Gary Pullano, associate editor