Abstract
Control of glyphosate-resistant giant ragweed is a challenge, particularly for soybean growers, because of limited effective post-emergence (POST) herbicide options. Many soybean growers in no-till production systems use 2,4-D in burndown application for control of broadleaf weeds, including giant ragweed. Field experiments were conducted at David City, NE, in 2012 and 2013 to evaluate 2,4-D followed by PRE or POST herbicide programs for control of glyphosate-resistant giant ragweed in glyphosate-resistant soybean. Results suggested that burndown application of 2,4-D or saflufenacil plus imazethapyr resulted in 89 to 99% control of giant ragweed at 21 days after treatment. Burndown-only treatments of S-metolachlor plus metribuzin or sulfentrazone plus cloransulam resulted in poor control (≤65%) of giant ragweed and reduced soybean yield (≤ 577 kg·ha-1). Burndown application of 2,4-D followed by saflufenacil plus imazethapyr, S-metolachlor plus metribuzin, or sulfentrazone plus cloransulam applied pre-emergence (PRE) or cloransulam, chlorimuron, fomesafen, imazethapyr, or lactofen in tank-mixtures with acetochlor applied POST resulted in 87% to 99% giant ragweed control, reduced density to ≤7 plants m-2, and resulted in soybean yield from 2519 to 3823 kg·ha-1. There was no difference among and between 2,4-D followed by PRE or POST herbicides for giant ragweed control, density, or soybean yield, indicating all the two pass herbicide programs were effective. It is concluded that glyphosate-resistant giant ragweed can be effectively controlled in soybean by including 2,4-D in burndown program followed by PRE or POST herbicides tested in this study.
Highlights
Soybean (Glycine max L.) is the most prevalent oilseed crop in the United States and it is the second most common field crop after corn [1]
We hypothesized that a combination of 2,4-D as burndown followed by PRE herbicides including saflufenacil plus imazethapyr, S-metolachlor plus metribuzin, sulfentrazone plus cloransulam, or POST herbicides such as cloransulam, chlorimuron, fomesafen, imazethapyr, or lactofen in tank-mixtures with acetochlor can effectively control glyphosate-resistant giant ragweed
A total of 13 herbicide programs including burndown followed by PRE or POST herbicides were compared for control of glyphosate-resistant giant ragweed (Table 1)
Summary
Soybean (Glycine max L.) is the most prevalent oilseed crop in the United States and it is the second most common field crop after corn [1]. In 2012, soybean was planted on 31.24 million ha in the United States [1]. Glyphosate-resistant soybean was first commercialized in 1996, and since it has been rapidly accepted by soybean growers [2]. In 2012, the National Agriculture Statistics Service of the U.S Department of Agriculture (USDA) reported that 91% of the soybean and 60% of corn ha were planted with glyphosate-resistant trait [3]. The success of glyphosate-resistant crop technology is due to broad-spectrum weed control that has facilitated adoption of conservation tillage [4]-[6]. 25 weed species worldwide have evolved resistance to glyphosate including 14 in the United States [8]
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