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When Soybeans Send Flowers

Pamela Smith
By  Pamela Smith , Crops Technology Editor
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The R-1 growth stage occurs in soybeans when first bloom begins to appear, and it can happen earlier than you might guess, Image courtesy of Shawn Conley, University of Wisconsin

New federal EPA labels for Engenia, FeXapan and XtendiMax have set a cutoff for postemergence applications in soybeans at 45 days after planting or the beginning of R-1 growth stage--whichever comes first.

R-1 growth stage means one open flower at any node on the main stem, reminds Shawn Conley, University of Wisconsin soybean and small grains specialist. Usually, the first flower is located between the fourth and sixth nodes.

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Tradition has held that soybeans generally start to flower after June 21, when the nights become longer. But, growers who plant ultraearly have found those first flowers can arrive earlier in the spring, thereby compressing the legal dicamba spray window, he notes.

The theory for the early flowering is the photosensitive soybean gets its desired dose of darkness very early in life. Conley says soybeans planted in more northerly regions naturally tend to be less sensitive to night and day.

The message is to forget the calendar approach to spraying and follow the label. And, remember: States may have more stringent spray cutoff dates for dicamba than the federal label.

Follow the latest from Pamela Smith, Crops Technology Editor, by visiting the Production Blogs at dtnpf.com or on Twitter @PamSmithDTN.

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