Decision criteria for optimizing postemergence johnsongrass control in soybean crops in Argentina

Abstract

-Field studies were established in Zavalla and Oliveros, Argentina, during four years in order to optimize Johnsongrass (Sorghum halepense (L.) Pers.) chemical control by means of the thermal calendar model in comparison with other criteria (weed height or days after sowing). The effect of three application dates of postemergence herbicides was determined by visual control, density of tillers originated from rhizome bud regrowth, and from crown and shoot bud regrowth, and soybean yield. Following the thermal calendar model criterion, applications during the second date afforded the best control. Weed height for the first date showed little variability between experiments but was highly variable in the second and third application dates, achieving in some cases values greater than 120 cm. For all years, no significant differences were detected for crop yield between the first and second application dates, and yields were always lower for the third date. The greatest rhizome bud regrowth was observed for the earliest application date and the highest crown and shoot bud regrowth was determined for the last application date. Parameters associated with control efficiency showed the best behaviour for the second date. However, plant height at this moment may interfere with herbicide application and the variability exhibited by this parameter highlights the risk of determining control timing using only one decision criterion.Index terms: weeds, herbicides, application timing. CRITÉRIOS DE DECISÃO PARA OTIMIZAR O CONTROLE DE CAPIM-MASSAMBARÁ EMCONDIÇÕES DE PÓS-EMERGÊNCIA NA CULTURA DA SOJA, NA ARGENTINA RESUMO -Foram conduzidos experimentos de campo durante quatro anos agrícolas em Zavalla e Oliveros, Argentina, com o objetivo de otimizar o controle químico de capim-massambará (Sorghum halepense (L.) Pers.), usando o modelo do calendário térmico em comparação com outros critérios de decisão (altura da planta daninha ou dias após a semeadura). O efeito do herbicida foi determinado por avaliação visual, densidade de perfilhos originados de rebrota de rizomas e de touceira e caule, e rendimento de grão de soja. As aplicações segundo o critério do calendário térmico mostraram o melhor controle. A altura da planta daninha na primeira época evidenciou pouca variabilidade entre tratamentos, mas foi muito variável pela segunda e terceira época, atingindo, em alguns casos, valores maiores que 120 cm. Os rendimentos da cultura na primeira e segunda época não diferiram entre si e superaram o rendimento da terceira época. A maior densidade de rebrota de rizomas foi observada na primeira época de aplicação, e o maior rebroto de touceira e caule foi determinado na terceira época. Os parâmetros associados com a eficiência mostraram o melhor comportamento na segunda época. Contudo, a altura da planta nesse momento pode interferir com a aplicação do herbicida e a variabilidade mostrada por esse parâmetro salienta o risco de determinar a época de controle usando só um critério de decisão.Termos para indexação: planta daninha, he...

An individual‐based model of seed‐ and rhizome‐propagated perennial plant species and sustainable management of Sorghum halepense in soybean production systems in Argentina

“…Failure to control Johnsongrass is a significant threat to soybean-dominated agriculture in Argentina, since competition with crops can result in yield loss of ca. US$ 300 million a year (Beltrano & Montaldi, 1979;Colbert, 1979;Tuesca, Puricelli, Nisensohn, Faccini, & Papa, 1999). Considering current herbicide use and the widely adopted no-tillage cropping systems, more cases of evolved herbicide resistance can be expected (Valverde, 2010), which if not addressed proactively or promptly will essentially mean growers have no herbicides to use in the near future.…”

Theoretical assessment of persistence and adaptation in weeds with complex life cycles

“…Herbicide efficiency The herbicide efficiency on Johnsongrass aboveground material depends on the developmental stage of the plants, with small young plants killed with higher efficiency than larger older plants (Tuesca et al 1999, Dogan & Boz 2005, Johnson & Norsworthy 2014. The efficiency also varies between years due to environmental factors and application timing (Vidrine 1989, Tuesca et al 1999. Johnson et al (2003) and Johnson & Norsworthy (2014) report the investigated ACCaseinhibitors to have a higher efficiency on Sorghum halepense than ALS-inhibitors included in their studies.…”

“…Herbicide application is expected to kill solely susceptible plants or partly resistant heterozygotes with an efficiency h or (1 − k h ) h , respectively. Due to inadequate translocation of herbicides into the rhizomes and their dormant buds, they are only partly controlled by the herbicide (Beasley 1970, Tuesca et al 1999). Therefore when shoots are killed by herbicide application but not the parent rhizome, shoots may eventually resprout from the rhizome (Beasley 1970, Tuesca et al 1999).…”

“…Due to inadequate translocation of herbicides into the rhizomes and their dormant buds, they are only partly controlled by the herbicide (Beasley 1970, Tuesca et al 1999). Therefore when shoots are killed by herbicide application but not the parent rhizome, shoots may eventually resprout from the rhizome (Beasley 1970, Tuesca et al 1999). This resprouting reduces the effective herbicide efficiency on rhizome shoots h T compared to the herbicide efficiency on seedlings h L (Vidrine 1989).…”

“…The fragmented rhizomes in shallow layers are exposed to low temperatures during winter, leading to increased mortality (Hull 1970, Warwick & Black 1983). Additionally, rhizome fragmentation is reported to maximize bud sprouting (McWhorter & Hartwig 1965), allowing for an enhanced control of Johnsongrass plants originating from rhizomes by the herbicide (Hull 1970, Tuesca et al 1999).…”