Title : Effects of Dicamba Micro-Rates on sensitive crops
Abstract:
I n order to control glyphosate resistant weeds, Dicamba-Tolerant (DT) Soybeans were plated at about 20 million US acres in 2017. It is believed that the number of acres will increase in 2018 season, which created a concern that the widespread use of dicamba-based herbicides in DT soybeans can result in un-intended drift due to windy conditions in USA. Therefore, the objective of this study was to establish some baseline indicators on the injury of potentially sensitive crops (eg. non-dicamba-tolerant soybeans, grapes and tomato) to six rates of three dicamba-based herbicides (Clarity, Engenia and XtendiMax.Field study was conducted in 2016and 2017 as a split-plot design with 6dicamba rates, 3 application times and 4replications. Dicamba rates were: 0; 1/10; 1/100; 1/500; 1/1000; 1/1500 of the label rate of three dicambaherbicides (560 g ai/ha). Plots had four rows of each soybean type (conventional,organic, RoundupReady,Liberty-Link),and Dicamba-tolerant soybeans(as a check) as well as pot-grown grape plants (2nd year of growth) and tomato seedlings.There were three application times of dicamba (eg. V2 (soybean 2ndtrifoliate), beginning flower (R1) and R2 (full flower) and corresponding size of grapes and tomato.As micro-rates increased, the crop growth parameters were significantly impacted, including: reductions in plant height, alterations in branching pattern, delayed days to canopy closure and delayed dates of flowering, reductions in flower number, delayed dates of physiological maturity, and most importantly reductions in soybean yield. The foregoing negative impacts were dependent on correspondence of application date with the soybean growth stage; with V7/R1 stage being the most dicamba sensitive. The 1/10 rate killed grapes (1st timing) and severely injured tomato (80%). However, there was only temporary injury in the 2nd timing in grapes. The 1/100 (and 1/1000) rate provided only transient symptoms in grapes and tomato (both timings). This is suggesting that grapes and tomato are not as sensitive to dicamba as the non-dicamba soybeans. These results clearly showed that non-DT soybeans were sensitive to even very low micro-rates of Clarity, Engenia and XtendiMax, hence, efforts should be made to avoid drift of dicamba onto non-DT soybeans.
