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1 October 2018 Injury Criteria Associated with Soybean Exposure to Dicamba
Matthew R. Foster, James L. Griffin
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Abstract

Research conducted in the field identified 14 injury criteria associated with dicamba (Clarity® diglycolamine salt) applied at 0.6 to 280 g ae ha-1 (1/1,000 to 1/2 of 560 g ha-1 use rate) to indeterminate soybean at V3/V4 or R1/R2. For each criterion, injury was rated using a scale of 0=no injury, 1=slight, 2= slight to moderate, 3=moderate, 4=moderate to severe, and 5=severe. Greatest crop injury 15 d after treatment (DAT) was observed for dicamba rates of 0.6 to 4.4 g ha-1 for upper canopy pale leaf margins (3.8 to 4.2) at V3/V4 and for terminal leaf cupping (4.1 to 5.0) at R1/R2, and for rates of 0.6 to 8.8 g ha-1 for upper canopy leaf cupping (3.8 to 4.8) and upper canopy leaf surface crinkling (3.4 to 4.4) at V3/V4. Injury 15 DAT was equivalent to the nontreated control for dicamba rates as high as 4.4 g ha-1 for lower stem base swelling at V3/V4 and for upper canopy leaf rollover/inversion and terminal leaf necrosis at R1/R2; for rates as high as 8.8 g ha-1 for leaf petiole base swelling and stem epinasty at R1/ R2, and lower stem base lesions/cracking (V3/V4 and R1/R2 average); and for rates as high as 17.5 g ha-1 for lower leaf soil contact at V3/V4 and leaf petiole droop at R1/R2. The response to increasing dicamba rate observed for the injury criteria was in contrast to the steady increase in visual injury and plant height reduction rated as 0 to 100%. The moderate to severe upper canopy leaf cupping, pale leaf margins, and leaf surface crinkling, and terminal leaf cupping 15 DAT with dicamba at 0.6 to 4.4 g ha-1 corresponded to soybean yield loss of 1% to 9% for application at V3/V4 and 2% to 17% at R1/R2.

Nomenclature: Dicamba; soybean, Glycine max (L.) Merr

© Weed Science Society of America, 2018.
Matthew R. Foster and James L. Griffin "Injury Criteria Associated with Soybean Exposure to Dicamba," Weed Technology 32(5), 608-617, (1 October 2018). https://doi.org/10.1017/wet.2018.42
Received: 6 January 2018; Accepted: 6 May 2018; Published: 1 October 2018
KEYWORDS
Crop injury assessment
Herbicide-resistant crops
Off-target movement
spray drift
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