Matt Morris, Extension Educator, Frederick County (mjmorris@umd.edu)
Dicamba tolerant soybeans, marketed under the trade name Roundup Ready Xtend will be available to Maryland growers for the 2017 growing season. This line of soybeans will combine previous Roundup Ready technology with a tolerance to the herbicide dicamba. While this new dicamba tolerance may be useful in combatting certain tough-to-control weeds including marestail and palmer amaranth, caution needs to be taken when making applications of dicamba. Problems with dicamba applications may arise due to the sensitivity of certain crops to dicamba. Exposure can occur due to drift, volatility, or a non-target application. Below are some recommendations to consider when utilizing new dicamba tolerant technologies.
Know the location of sensitive crops:
Talk with your neighbors and know where crops such as tomatoes, grapes, alfalfa, and non-tolerant soybeans are located. This will aide in the decision to use dicamba near these crops, especially if a prevailing wind is headed their direction. In addition, buffer zones of 110’ (220’ if a 22oz/ac rate is exceeded), will need to be maintained between dicamba application sites and sensitive crops. These two websites listed below contain a (incomplete) list of some sensitive crops in your area:(Link Here)
Dicamba type:
The only dicamba products that will be approved for in-crop use with Xtend soybeans will be XtendiMax from Monsanto, FeXapan from Dupont, and Engenia from BASF. These are lower volatility formulations than other dicamba products and are designed for the dicamba tolerant soybeans.
Rates:
Engenia – Dicamba tolerant soybeans – max of 12.8 fl oz/application and 51.2 oz/season.
FeXapan and XtendiMax – Dicamba tolerant soybeans – max of 44 fl oz/preplant application, 22 fl oz/postemergence application, and a max of 88 fl oz/season.
Nozzle selection:
Engenia – Only TTI11004 and TTI11005 are currently approved.
FeXapan and XtendiMax – Apply large droplets with specific nozzles. Do not use flat fan nozzles that product driftable fines. Use TTI11004 or nozzles listed on the EPA-mandated product websites.
Spray adjuvants and water conditioning:
Ammonium sulfate (AMS) CANNOT be mixed with these new dicamba formulations. AMS is commonly used as a water conditioning agent for glyphosate applications. Adding AMS will increase volatility of the dicamba. Also, certain spray adjuvants and herbicide tank mix partners are not compatible with the new dicamba formulations. Always consult the label before mixing.
Recordkeeping:
Always keep records of where you’ve planted dicamba tolerant soybeans. This can help avoid costly misapplications to a crop that is not tolerant to dicamba. It will be extremely important to convey this information to custom application companies or employees on your farm.
Wind Speed, temperature, and temperature inversions:
When applying these new dicamba products the optimal wind speed is 3-5mph. Applications are prohibited when wind speeds are above 15mph; however, great caution and even stopping spraying when wind speeds are above 10mph would be ideal.
As temperature increases so does the volatility of dicamba. Caution should be used when applications are made in hot, humid weather.
Caution should also be taken when wind speeds are below 3mph as this could indicate the presence of a temperature inversion. Inversions are another cause of vapor drift. Other indicators of a temperature inversion include low hanging smoke or dust, morning fog or frost, clear and still nights with little to no cloud cover, and ground temperatures cooler than early morning air temperatures.
Multiple applications and weed height:
Multiple herbicide applications with the same mode of action within a single season selects for herbicide resistance. Avoid using dicamba on tolerant soybeans more than once in a season. If possible, a pre-emergence herbicide should be applied before or at planting. It is also important to remember that weeds should be targeted at 4” of height or less for successful control.
Application Suggestions:
Keep ground speeds below 15 mph and nozzle pressures as low as possible to maintain the desired application rate. Boom height should be no more than 24” above the crop or weed canopy. If a weed is 4” tall, boom height should not exceed 28”.
Most importantly:
ALWAYS READ AND FOLLOW PESTICIDE PRODUCT LABELING. It is a violation of Federal and state law to use any pesticide product in a manner inconsistent with its labeling.
The U.S. EPA will allow its approval of dicamba tolerant soybeans to run until the end of 2018. At that point they will consider whether or not to renew approval based on the amount of problems that arise as a result of this new technology. In order to have this technology in the future, proper stewardship by the grower is essential. If you have questions regarding the use of dicamba tolerant soybean technology or dicamba itself please contact Matt Morris @ 301-600-3578 / mjmorris@umd.edu or contact your local Extension office for more information.
References and other Resources:
-University of Illinois Extension. The Bulletin. Dicamba and Soybean: What to Expect in 2017. http://bulletin.ipm.illinois.edu/?p=3765
-Purdue University Extension ID-453-W. 2,4-D- and Dicamba Tolerant Crops- Some Facts to Consider. https://www.extension.purdue.edu/extmedia/id/id-453-w.pdf
-Reviewed by Ron Ritter, Professor Emeritus, University of Maryland
