2018 ASHS Annual Conference

Iron (Fe) is commonly used in the turfgrass industry to correct nutrient deficiencies in high pH soils, for disease suppression, moss suppression, or improved turf aesthetics. Particularly in the lawn care industry, Fe may be tank-mixed with 2,4-D containing herbicides to control weeds in the lawn while simultaneously providing Fe nutrition. Since FeSO₄ is known to antagonize certain herbicides and since other cations are known to antagonize water soluble 2,4-D formulations, our objective was to evaluate the influence of various sources of iron on 2,4-D dimethylamine efficacy when tank-mixed. Greenhouse and field experiments evaluated three iron sources: FeSO₄ heptahydrate, Fe diethylenetriaminepentaacetic acid (DTPA), and Fe hydroxyethylenediaminetriacetic acid (HEDTA). FeSO₄ and FeDTPA are commonly marketed for nutrition, whereas FeHEDTA is marketed for broadleaf weed control. Iron application rates were chosen based on label recommendations or common use rates. The iron sources were applied to dandelions with or without 2,4-D dimethylamine at 1.6 kg ae ha^-1 in the greenhouse experiment. The field experiment applied six treatments (nontreated, 2,4-D + FeSO₄, 2,4-D + FeDTPA, 2,4-D + FeHEDTA, and FeHEDTA) to dandelions in October of 2016 and 2017. Without the inclusion of 2,4-D, FeHEDTA reduced dandelion mass compared to other iron sources and the nontreated plants in the greenhouse experiment. This was from a rapid injury to dandelion foliage from FeHEDTA after application followed by a partial recovery of the dandelion. Both 2,4-D applied alone and 2,4-D tank-mixed with FeHEDTA, controlled dandelions in the greenhouse experiment. However, both FeSO₄ and FeDTPA reduced weed control when tank-mixed with 2,4-D. In the field, 2,4-D alone provided the highest control of mature dandelions and superior control to a single application of FeHEDTA alone. All three iron sources (FeSO₄, FeDTPA, FeHEDTA) antagonized 2,4-D when applied as tank-mixtures to field plots. Overall, results suggest that each of the iron fertilizers can antagonize 2,4-D dimethylamine and that applicators should avoid tank-mixing iron fertilizers when applying postemergence broadleaf herbicides.