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Morning and evening restrictions on the 2019 Engenia, FeXapan, Tavium, and Xtendimax Labels (06/06/19)

Off-target movement of dicamba applied over the top in tolerant soybeans has been a problem in both 2017 and 2018.

Off-target movement of dicamba applied over the top in tolerant soybeans has been a problem in both 2017 and 2018. So, EPA issued 2018 labels that called for applications only during daylight hours. The goal was to avoid problems with air temperature inversions which are often in place at night.

2018 again saw significant off-target movement in many areas of the soybean belt, so, based on university observations, EPA issued stricter labeling for 2019. Essentially, the above formulations can only be applied one hour after sunrise until two hours before sunset. In general, we know based on numerous observations by NDAWN, the University of Minnesota, and others, that inversions typically begin to form most evenings two to three hours before sunset. They then dissipate an hour to two hours after sunrise, hence the new labeling. However, it should be noted that if conditions are just so, inversions can begin to set in three to five hours before sunset and linger two to three hours after sunrise. So, if an inversion is in place outside of the labeled hours, you must cease applications.

This means applicators must know the Sunrise and Sunset time on EACH day of application and at the site of application. Sunrise and Sunset times vary every day due to the orientation of the Earth relative to the Sun. These times also vary every day due to the specific location of the application at any given point on the Earth. As you move from East to West the timing changes. As you move from South to North, during the early summer months, the duration of each day increases until the summer solstice, June 21. Then it begins to decrease. (See the following two graphics to illustrate this.) Therefore, successfully meeting this label directive requires you to look up the Sunrise and Sunset times for the location and date that you make an application. Not doing so means you are likely NOT in compliance with the label, and you will risk greater off-target movement.

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The following picture demonstrates that Sunrise and Sunset timing can be heavily influenced by local topography, like hills, ridges, and valleys. Further, trees, especially in a well-developed shelterbelt, can also alter the Sunrise and Sunset time. While the label is silent on this, it can still make a huge difference on timing as well as the intensity of air temperature inversions.

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Sunrise and Sunset times are calculated for any position on the globe by the U.S Naval Observatory. Their website can calculate a table, by date, for a particular city or town and they will calculate them more specifically if you know the longitude and latitude of your location. The National Weather Service also publishes Sunrise and Sunset times. However, it is based on U.S. Naval Observatory calculations.

It should be noted; this article primarily focusses on a narrow part of the label for the above products. There are a myriad of other weather variables and restrictions as well. The applicator is directed to comply with ALL mandatory label statements and not just the one dealing with hours of application.

A narrated PowerPoint presentation on this topic was posted this past April on Vimeo. It runs about 7.5 minutes and can be viewed on computer, smart phone, or tablet with a network connection. 

 

Andrew A. Thostenson

Pesticide Program Specialist

 

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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