Abstract
AbstractDicamba residues in sprayers are difficult to remove and may interact with subsequent herbicides, including contact herbicides labeled for use in soybean. Without proper tank cleanout, applicators treating dicamba-resistant and non–dicamba resistant crops are at risk of contaminating the spray solution with dicamba residue from previous applications. Experiments were conducted in Fayetteville, AR, in 2018 and 2019, with the first experiment evaluating consequences of dicamba tank contamination with contact herbicides and the second experiment addressing the impact of dicamba exposure on a glufosinate-resistant soybean cultivar relative to a contact herbicide application. Experiments for tank contamination and timing of dicamba exposure were designed as a three-factor and a two-factor randomized complete block with four replications, respectively, considering site-year as a fixed effect in each experiment. Dicamba at 0, 0.056, 0.56, and 5.6 g ae ha−1 was applied alone, with glufosinate, with acifluorfen, or with glufosinate plus acifluorfen to V3 soybean. Dicamba applied in combination with contact herbicides exacerbated visible auxin symptomology over dicamba alone at 21 and 28 d after treatment (DAT), while dicamba at 5.6 g ae ha−1 reduced soybean height. Injury and height reductions caused by dicamba mixtures with contact herbicides did not reduce grain yield. In the second experiment, dicamba was applied at 2.8 g ae ha−1 at VC, V1, V2, and V3 and at 3, 7, and 10 d after a glufosinate application to V3 soybean (DATV3). Greater soybean injury was observed when dicamba exposure followed a glufosinate application than when dicamba preceded glufosinate or was applied in a mixture with glufosinate, with yield reductions resulting from 7 and 10 DATV3 dicamba applications. Dicamba exposure in the presence of contact herbicides resulted in increased auxin symptomology and can be intensified if soybean are exposed to dicamba following a contact herbicide application.
Highlights
Producers frequently combine multiple herbicides into a single application to achieve greater weed control as well as save application costs by reducing the number of trips across the field (Jordan 1995; Rhodes and Coble 1984; Zhang et al 2005)
One advantage of combining herbicides with different sites of action (SOAs) is increasing the longevity of a single herbicide or SOA. This is important for producers facing herbicide-resistant weed issues, especially as a tremendous amount of selection pressure can be placed on POST applications due to the size and number of weeds present at application (Hydrick and Shaw 1994; Lanclos et al 2002; Norsworthy et al 2012; Webster and Shaw 1997)
Contact herbicides can antagonize the activity of systemic herbicides; for example, glufosinate has been documented to antagonize the efficacy of clethodim on goosegrass [Eleusine indica (L.) Gaertn.] by disrupting cell membranes via accumulation of toxic levels of ammonia, which results in reduced translocation of clethodim (Burke et al 2005)
Summary
Producers frequently combine multiple herbicides into a single application to achieve greater weed control as well as save application costs by reducing the number of trips across the field (Jordan 1995; Rhodes and Coble 1984; Zhang et al 2005). Dicamba applied alone caused considerably more soybean injury than other common POST herbicides alone at field use rates (≈40% increase) and resulted in an 18% increase in auxin injury when combined with fomesafen at 330 g ai ha−1 at the V3 growth stage compared with dicamba alone.
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