| Summary: | Growers commonly mix foliar fertilizers with postemergence (POST) herbicides to reduce application costs and/or to decrease soybean injury. Field studies conducted in 2015 and 2016 in Stoneville, MS, evaluated the impact on weed control and soybean (<i>Glycine max</i> (L.) Merr) injury, growth, and yield when combining a blended foliar fertilizer with POST herbicide applications. Herbicide treatments included no herbicide and glyphosate alone and in combination with <i>S</i>-metolachlor, fomesafen, or lactofen. The blended foliar fertilizer was applied at 0, 0.39, and 0.78 kg a.i. ha<sup>−1</sup>. In the Weed Control Study, 14 antagonistic effects at various evaluations were detected on Palmer amaranth (<i>Amaranthus palmeri</i> (S.) Wats) and barnyardgrass (<i>Echinochloa crus-galli</i> (L.) P. Beauv.) control 7, 14, and 21 d after treatment (DAT) when a blended foliar fertilizer at 0.39 or 0.78 kg a.i. ha<sup>−1</sup> was mixed with glyphosate alone or combined with <i>S</i>-metolachlor, fomesafen, or lactofen. Of the 14 total effects, nine were detected with foliar fertilizer at the higher rate of 0.78 kg a.i. ha<sup>−1</sup>. Seven antagonistic effects were detected for both weed species regardless of herbicide treatment or foliar fertilizer rate. The only treatment combination in which an antagonistic effect was not detected was glyphosate plus lactofen plus foliar fertilizer at 0.78 kg a.i. ha<sup>−1</sup>. Blended foliar fertilizer did not influence soybean injury. In the Agronomic Study, blended foliar fertilizer did not impact soybean injury, height, dry wt., nutrient conc., or yield. Foliar fertilizer in combination with POST soybean herbicides did not reduce soybean injury and produced inconsistent effects on weed control across herbicide treatments and between weed species.
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