Kentucky: Dicamba – Postemergence Applications – Restrictions Reminders

Herbicide spraying in soybean field. ©Debra L Ferguson Stock Photography

The month of June has arrived and so too will postemergence soybean applications, many of which are likely to contain the dicamba formulations of Xtendimax, Engenia, or FeXapan. As we approach these coming weeks when many of our dicamba application are likely to be applied it is time to have a refresher on the label restrictions and guidelines for applying these products.

Record Keeping: Twenty-one points of data must be recorded for each field that receives a dicamba application. Weather conditions of wind speed, wind direction, and temperature must be recorded at the beginning and end of each application. Also remember that wind speed and direction should be taken at the boom height.

Record keeping can seem very burdensome to us all, especially when you have an endless number of acres ahead of you and limited time. Remember though that well-kept records are you best friend when/if you are inspected for a potential injury case.

Sensitive Areas and Sensitive Crops: There is a distinction between sensitive areas and sensitive crops for the dicamba labels. Distinguishing the differences in these two areas is important in that they are treated differently when the wind is blowing towards them from a field receiving a dicamba application.

  • A sensitive area is any non-crop area that potentially harbors an endangered or threatened species, such as native vegetation, wooded areas, fence lines, and road ditches.
  • A sensitive crop is any crop that is susceptible to dicamba such as non-dicamba-tolerant soybean, tobacco, tomatoes, grapes, fruit trees, and residential areas.

If the wind is blowing towards a sensitive area then a buffer (110 ft) must be maintained between the application site and the sensitive area.

If the wind is blowing towards a sensitive crop, DO NOT APPLY. The distance of a sensitive crop downwind is undefined, but we would suggest that if it is within 0.5 miles then the applicator should strongly consider not making the application.

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It is the responsibility of the applicator to know what sensitive crops are surrounding the field receiving a dicamba application. It is strongly encouraged for you to revisit with owners of neighboring field to make sure that the crop planted is still consistent with what was discussed in past conversations as things can often change, especially with this past planting season.

Wind Speed: Applications can only be made when wind is between 3 and 10 mph and when blowing away from any sensitive crops as discussed above. The minimum weed speed is just as critical as the maximum wind speed. Applying dicamba when winds are below 3 mph significantly increases the chances of applying into a temperature inversion.

Time of Day: Applications are only allowed between sunrise and sundown. These restrictions have been put in place to avoid temperature inversions that will setup during the majority of nights in the summer months of June and July.

Tracking of temperature inversions by our neighboring states over the past couple of season suggest that temperature inversions often start setting up about two hours prior to sunset and dissipate approximately two hours after sunrise. Based on this knowledge we would encourage you to only apply from two hours after sunrise to two hours prior to sunset.

Nozzle Selection: Use only approved nozzles that can be found on the label websites listed at the end of this article. The websites will also list the approved pressures for each nozzle. These restrictions on nozzles and pressures assure that driftable fines are minimized and thus minimize movement of droplets off-site, assuming all other restrictions are followed. Remember that even large droplet can move off target in high wind conditions.

Boom Height: The height of the spray boom at the time of application is often overlooked, but plays a critical role in the drift potential of an application. The higher the boom is from the target the longer the droplet must remain in the state of fall.

This extended period of time leads to increased chances of horizontal movement by wind currents and evaporation of the droplet causing a decrease in size and increased likelihood of drift. Lowering the boom to the required height of 24 inches from the target will significantly reduce the potential of off-target movement.

Running a boom height at 24 inches can be nerve racking for any applicator operating a wide boomed sprayed in many of our Kentucky fields that certainly are not flat. Our suggestion would be to lower travel speeds to allow for the ability to more accurately control boom height while avoiding damage from running boom tips into the ground.

Tank Mix Partners and Adjuvants: Use only approved tank mix partners that are found on the label websites listed at the end of the article. Some of the tankmix partners will require the addition of an approved drift reduction agent, which are also listed on the website.

Remember to only use the trade name products that are listed on the website. A generic product with same active ingredient as a product on the approved list cannot be used as formulations vary from product to product even with the same active ingredient.

DO NOT USE Ammonium sulfate: Ammonium sulfate that is either added to the tank or is a residue from previous applications will cause the salts to dissociate from the dicamba molecule creating a dicamba acid. Dicamba acid is the most volatile form of dicamba and will most likely move off-target to neighboring sensitive crops.

These are just a few reminders of the dicamba label restrictions, as always make sure to review the label and label websites.

We are very aware that following all the strict restrictions on these dicamba labels is difficult, especially in the months of June and July and often may be impossible.

It is imperative though that we follow these label restrictions as to decrease the level of wide spread off-site movement that occurred last season. Applicators and farmer must also understand that there are some fields that are just not appropriate for a dicamba application due to surrounding sensitive crops and may need an alternative weed control method or herbicide.

It is undeniable the amount of utility that the dicamba-tolerant soybean system brings to those farmers who have infestations of Palmer amaranth and waterhemp. The level of stewardship of these dicamba

products this season and ability to reduce off-target movement will go a long way in determining the availability of this system in the years to come.

Approved Tank Mix and Nozzle Websites:

BASF Engenia® Herbicide Tank Mix: www.engeniatankmix.com

Monsanto Xtendimax® Application Requirements: www.xtendimaxapplicationrequirements.com

DuPont FeXapan® Application Requirements: www.fexapanapplicationrequirements.dupont.com


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