Abstract
Common ragweed emerges early in the season in Nebraska, USA and is competitive with soybean; therefore, preplant herbicides are important for effective control. Glyphosate has been used as a preplant control option; however, confirmation of glyphosate-resistant (GR) common ragweed in Nebraska necessitates evaluating other herbicide options. The objectives of this study were to (1) evaluate the efficacy of preplant (PP) herbicides followed by (fb) glufosinate alone or in tank-mixture with imazethapyr, acetochlor, or S-metolachlor applied post-emergence (POST) for control of GR common ragweed in glufosinate-resistant soybean; (2) their effect on common ragweed density, biomass, and soybean yield; and (3) the partial economics of herbicide programs. A field experiment was conducted in a grower's field infested with GR common ragweed in Gage County, Nebraska, USA in 2015 and 2016. Preplant herbicide programs containing glufosinate, paraquat, 2,4-D, dimethenamid-P, cloransulam-methyl, or high rates of flumioxazin plus chlorimuron-ethyl provided 90–99% control of common ragweed at 21 d after treatment (DAT). The aforementioned PP herbicides fb a POST application of glufosinate alone or in tank-mixture with imazethapyr, acetochlor, or S-metolachlor controlled GR common ragweed 84–98% at soybean harvest, reduced common ragweed density (≤20 plants m−2) and biomass by ≥93%, and secured soybean yield 1,819–2,158 kg ha−1. The PP fb POST herbicide programs resulted in the highest gross profit margins (US$373–US$506) compared to PP alone (US$91) or PRE fb POST programs (US$158). The results of this study conclude that effective and economical control of GR common ragweed in glufosinate-resistant soybean is achievable with PP fb POST herbicide programs.
Highlights
Common ragweed (Ambrosia artemisiifolia L.) is a native, herbaceous, annual weed that belongs to the Asteracea family and is commonly found throughout temperate North America (Dickerson and Sweet, 1971; Coble et al, 1981)
Results of this study conclude that PP herbicide options are available for early season control of GR common ragweed; a follow-up POST application of glufosinate alone or in tank-mixture is needed to achieve season-long control
Most of the PP herbicides tested in this study provided effective control (>95%) of common ragweed during soybean emergence and establishment
Summary
Common ragweed (Ambrosia artemisiifolia L.) is a native, herbaceous, annual weed that belongs to the Asteracea family and is commonly found throughout temperate North America (Dickerson and Sweet, 1971; Coble et al, 1981). Coble et al (1981) reported that four common ragweed plants 10 m−1 row reduced 8% soybean yield. Shurtleff and Coble (1985) and Weaver (2001) reported that 1.6 common ragweed plants m−1 row reduced soybean yield by 12 and 11%, respectively. Common ragweed is a monoecious species that has the potential to produce several thousand seeds per plant. A large (2.4 kg fresh weight) common ragweed plant can produce up to 62,000 seeds (Dickerson and Sweet, 1971) and can grow up to 2 m in height (Bassett and Crompton, 1975; Clewis et al, 2001). Allowing common ragweed seeds to enter the seed bank can lead to long term concern as seeds can remain viable in the soil for 39 years (Bassett and Crompton, 1975)
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