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Expert advice on innovation in precision agriculture

October 11, 2017

Precision ag for on and off-target situations: A focus on dicamba

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Reports of damage across millions of acres of North America has left officials  in the United States questioning whether dicamba, a powerful group four herbicide, should be restricted in order to protect vulnerable crops from spray drift.

The herbicide’s tendency toward volatility and drift during spraying has been a hot topic of discussion in the agricultural community. While highly effective, the herbicide’s benefits are best seen when properly managed through the use of precision agriculture technology – including the observation and documentation of crop production applications.



In 1996, glyphosate tolerant soybeans were introduced into the market and 20-years later, the majority of all soybeans acres in North America are glyphosate tolerant. High repeat usage of glyphosate on soybeans and rotation crops such as corn and cotton has increased natural selection pressure and caused weed populations to evolve into herbicide resistant species and variants.

Before precision agriculture technologies were an available option, record keeping for crop and herbicide rotation was kept manually. Linking multiple year-rotation and herbicide application data was not as common and the possibility of weed resistance to glyphosate was considered speculative by many. Twenty years later an estimated 75 per cent of the soybean acres in North America have glyphosate resistant weeds, ultimately leading to the development of dicamba-tolerant soybeans.

If the tools to manage and track cropping rotations and herbicide options had existed in previous decades, the advent of glyphosate resistant weeds may have been delayed. In today’s agriculture, precision agriculture can provide the tools to better manage crop and herbicide rotations to avoid future resistance development.



To increase precision of dicamba spraying, farmers can add a separate piece of equipment onto their sprayer, referred to as a direct injection system.

“With this piece, a farmer can mix Roundup® and water in the main sprayer tank, while the direct injection system works on the side, adding dicamba into the spray stream,” explains Ryan Adams, P.Ag, Manager of Analytics, Crop Production Services(CPS) Canada.. “Using this, the farmer can control the rate of dicamba on-the-fly.”

For example, a full-pass on the edge of a field can be done without dicamba if the neighbouring field has a susceptible crop, or a certain area prone to weeds can be mapped out and receive dicamba while the rest of the field is sprayed with glyphosate.

“When it comes to general management decisions, making sure you’re using the proper products is crucial,” Wilt Billing, P.Ag, Corn and Soybean Product Line Manager with CPS recommends. “Use dicamba products that have been brought to market with stabilizing components reducing volatility.” Currently available is Monsanto’s Roundup Ready® Xtend herbicide System and BASF’s Engenia®. “These two herbicides have components in them designed to significantly reduce the volatility of dicamba,” explains Billing.

“Using the correct nozzle is critical,” says Billing. “Choose a nozzle that produces extremely coarse or ultra-coarse droplets because larger droplets will fall faster and reduce offsite movement of the herbicide.” Maintaining a minimum spray application water volume of 10 gallons per acre helps eliminate volatilization and achieve coarser droplets. Using water volumes lower than 10 gallons produces finer spray particles more prone to drift.

Another management recommendation is to spray when weeds and the crop are smaller, allowing farmers to keep the sprayer boom closer to the ground. “The recommendation is to keep the boom no higher than 50 centimeters above the crop canopy, because as the boom rises, the chance of drift and volatilization does too,” Billing explains.

Keeping ground speeds slower than 25 kilometers per hour helps prevent volatilization as well. “A speed of 25 kilometers per hour sounds fast in the field,” says Billing, “but there are many farmers who operate sprayers even faster than the recommended speed.”

“Always spray under proper conditions,” warns Billing. “Wind speeds within five to 15 kilometers per hour are the recommendation for spraying dicamba and reducing the risk of drift or volatilization. Light winds (zero to three kilometers per hour) tend to be unpredictable and variable in direction. Spray when wind is blowing away from sensitive areas.”



Harnessing a powerful herbicide like dicamba is important for farmers, but users need to understand how to use it successfully and responsibly. “It just comes down to being smart and informed about the product,” says Adams.

“Drift and volatility are separate risks with the same result – damage to plant health,” explains Adams. “When people refer to dicamba drift, they’re talking about small particles – usually smaller than 150 micrometers – moving off-target during application. The particles drift into the air and any sort of wind will blow them onto other fields or areas where the herbicide can damage crops that aren’t dicamba-resistant.”

“The more prevalent risk of using dicamba is referred to as volatilization,” says Billing, referencing the chance the dicamba molecule doesn’t stay on the target plant, and instead volatizes up into the air as a gas.

When dicamba is sprayed on a crop, especially during high temperatures, it can volatize, or turn from liquid to gaseous state. Once a gas, it can be blown by wind off of the field and travel long distances in its gaseous state. “Dicamba is an aromatic oil. Once in gas form, if the gas settles onto a field of another susceptible crop, it can kill it,” says Adams.

“Dicamba is a selective herbicide that only kills certain plant types,” explains Adams. “For example, it’s used with soybeans that have a bred-in resistance for the chemical, whereas a normal soybean sprayed with dicamba will be damaged or killed.”

“When it comes to precision agriculture, there are a few things farmers can do to better manage dicamba herbicide use,” says Adams. “The first is documentation. If an issue occurs, having a written record of what happened is critical. Farmers should be documenting where they sprayed the product and when it went down as well as what the environmental conditions were at the time of application and if they were in the window of conditions that could cause volatilization.” Good record keeping can be extremely beneficial to farmers if any issues occur after spraying. It’s an important habit for farmers to develop and it’s something Echelon experts can easily help with and provide advice to farmers on.

In Canada, dicamba is primarily used on summer fallow and wheat crops in the southern regions of western Canada. For more information on using dicamba properly and benefiting from the power of the product, contact your local Crop Production Services retail.

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