January 31, 2017
Mary Ann Rose and Jonah Johnson
Crops resistant to dicamba and 2,4-D may prove to be invaluable tools to combat weed resistance. However, events of 2016 in the Southern states serve as an important lesson to growers who will plant these new crops for the first time this spring.
Dicamba-resistant soybeans were planted on thousands of acres last growing season despite no dicamba formulations being registered for over-the-top use. Widespread, illegal use of older dicamba formulations applied on Monsanto’s Roundup Ready 2 Xtend soybeans led to thousands of acres of injury, mostly to adjacent fields on non-dicamba resistant beans.
Fortunately, this upcoming growing season there are two low-volatility formulations of dicamba herbicide registered for in-crop use on dicamba-resistant soybeans: XtendiMax (Monsanto) and Engenia (BASF). Similarly, a low-volatility formulation of 2,4-D plus glyphosate (Enlist Duo) is registered for in-crop use in Enlist soybeans. These herbicides may be applied up to and including the R1 (first bloom) growth stage of soybeans.
The take-home message from last year’s events is to follow label requirements and technology agreements to the letter. The No. 1 requirement when making an in-crop application is to use only those products registered for this type of application. In-crop application of non-registered dicamba or 2,4-D formulations is against the law.
For the Xtendimax and Engenia products, the “over-the-top” use appears on a supplemental pesticide label, and growers must have a copy of the supplemental label in their possession to make the in-crop application (this is true for all uses that are exclusive to supplemental labels). The distinction between the product label and the supplemental label is that this label allows for in-crop use, which is extremely important. The restrictions that apply to in-crop use only appear on the supplemental label. Be sure to read both, with emphasis on restrictions appearing in the supplemental label if you will be using dicamba on resistant soybeans.
The new herbicides have many restrictions to reduce the risk of drift and injury to adjacent areas. No aerial applications are allowed. Specific spray nozzles and operating pressures that produce extra- and ultra-coarse droplets are required. Only a single nozzle and pressure appear on the XtendiMax and Engenia labels, and 23 nozzle and pressure combinations appear on the Enlist Duo label. Keep in mind you may need to purchase new nozzles for your sprayer to use these products legally.
Do not add ammonium sulfate to the dicamba formulations. Currently, no approved tankmix partners exist for these products, but both labels provide a web address where approved tank mixes and nozzle-pressure combinations may be listed in the future. Dow also has a website where acceptable tankmix partners for Enlist Duo are listed.
Do not apply these products if the wind speed exceeds 15 mph. All of these products prohibit application during a field-level temperature inversion, which can be a risk when winds are very light during cool, clear evenings or mornings. XtendiMax has a minimum wind speed of 3 mph. Purchasing a hand-held device for measuring wind speed at the application site is highly recommended.
Do not exceed ground speeds of 15 mph and keep the spray boom no more than 24 inches above the target. The minimum spray volume is 10 gallons per acre.
All of these herbicides prohibit spraying when the wind is blowing toward adjacent sensitive crops, specifically citing commercially grown tomatoes, fruiting vegetables, cucurbits, grapes and cotton.
The labels may confuse some growers on this point, because of the buffer zones given on the labels for “sensitive areas.” On pesticide labels, “sensitive areas” indicate habitats for endangered species, not sensitive crops. Growers also will need to pay close attention to the tank cleanout procedures to prevent injury to non-resistant crops they may spray at a later date.
In addition to drift management, the product labels also emphasize weed resistance management through minimum and maximum use rates, maximum weed size controlled, scouting, rotation of chemistries and other standard practices. There are also restrictions with respect to rainfall following application.
For your safety, note the differences in required personal protective equipment (PPE) among the products. Enlist Duo requires protective eyewear, chemical-resistant gloves and a chemical-resistant apron for mixing and loading. For the same tasks, XtendiMax requires chemical-resistant gloves and Engenia requires the chemical-resistant gloves plus a respirator. In addition, all of them require a long-sleeved shirt, long pants, shoes and socks. The PPE requirements do not appear on the supplemental labels — another reason why it’s essential to read both the product and supplemental label.
Because of the many requirements and learning curve associated with using the new technologies, the manufacturer websites are including educational information to help growers. Be sure to carefully read the product label, and for the two dicamba products, the supplemental labels as well.
Rose is director of the Pesticide Safety Education Program at Ohio State University Extension and Johnson is a field agronomist at DuPont Pioneer in southern Ohio.
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