Abstract
AbstractA meta-analysis of 11 previously published field studies was conducted with the objectives being to (1) estimate the no observable effects dose (NOED) for dicamba on susceptible soybean; (2) evaluate available evidence for hormesis, or increased soybean yield in response to low doses of dicamba; (3) estimate the dose of dicamba likely to cause measurable soybean yield loss under field conditions; and (4) quantify the relationship between visible injury symptoms and soybean yield loss. All studies that included visible injury data (N=7) reported injury symptoms at the lowest nonzero dicamba dose applied (as low as 0.03 g ae ha−1), and therefore a NOED could not be estimated from the existing peer-reviewed literature. Based on statistical tests for hormesis, there is insufficient evidence to support any claim of increased soybean yield at low dicamba doses. Future research should include a range of dicamba doses lower than 0.03 g ha−1to estimate a NOED and determine whether a hormesis effect is possible at or below dicamba doses that cause visible injury symptoms. Soybean is more susceptible to dicamba when exposed at flowering (R1 to R2 stage) compared with vegetative stages (V1 to V7). A dicamba dose of 0.9 g ha−1(95% CI=0.08 to 1.7) at the flowering stage was estimated to cause 5% soybean yield loss. When exposed at vegetative stages, dicamba doses that cause less than 30% visible injury symptoms (95% CI=23 to 49%) appear unlikely to cause greater than 5% soybean yield loss; however, if soybean is exposed at flowering, visible injury symptoms greater than 12% (95% CI=8 to 16%) are likely to be associated with at least 5% soybean yield loss.
Highlights
Dicamba-resistant soybean cultivars have recently been commercialized, and adoption of this genetically engineered trait has been widespread throughout soybean-growing regions of the United States
The purpose of this report is to update the meta-analysis by Egan et al (2014) and to add potentially useful information regarding the relationship of visible injury symptoms to soybean yield loss based on the new data that have been published in the last several years
Because visible injury was reported at the lowest dicamba dose in each study in which injury was evaluated, a no observable effects dose (NOED) value cannot be estimated from the existing published literature
Summary
Dicamba-resistant soybean cultivars have recently been commercialized, and adoption of this genetically engineered trait has been widespread throughout soybean-growing regions of the United States. Along with the commercial introduction of these cultivars, there have been many reports of soybean fields without the dicamba-resistance trait showing synthetic auxin herbicide symptoms. Many studies have been conducted to quantify the relationship between dicamba dose and soybean response. Since Egan and colleagues’ meta-analysis, additional studies have been published reporting the effects of dicamba on soybean yield. The purpose of this report is to update the meta-analysis by Egan et al (2014) and to add potentially useful information regarding the relationship of visible injury symptoms to soybean yield loss based on the new data that have been published in the last several years
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