Abstract
Glyphosate resistant (GR) Canada fleabane (horseweed) has quickly spread across southwestern Ontario and is a difficult weed to control in GR crops. Glyphosate dimethylamine (DMA)/2,4-D choline (Enlist Duo?TM Dow AgroSciences LLC), a new herbicide premix developed by Dow Agro Sciences, provides control of GR and other problematic weeds. The objective of this study was to compare single and sequential applications of glyphosate DMA/2,4-D choline for the control of GR Canada fleabane in GR corn. Three single applications of glyphosate (DMA)/2,4-D choline (1720 g·ae·ha-1) were evaluated: 1) preplant (PP) applied to Canada fleabane up to 10 cm diameter/height, 2) postplant 1 (POST 1) applied when Canada fleabane was up to 20 cm tall and 3) postplant 2 (POST 2) applied up to 30 cm tall Canada fleabane. Four sequential applications were also examined:1) PP followed by (fb) POST 1, 2) PP fb POST 2, 3) POST 1 fb POST 2 and 4) PP fb POST 1 fb POST 2. The single applications provided 69%-86% control of the GR Canada fleabane while the sequential applications increased control to 92%-100%. Three applications did not provide an increase in control over a sequential two-pass application at 8 weeks after the application (WAA). Results from this research indicate that a sequential 2-pass application of glyphosate DMA/2,4-D choline provided acceptable control of GR Canada fleabane in corn.
Highlights
Conyza canadensis, commonly known as Canada fleabane, horseweed or mare’s tail, is a facultative winter annual weed meaning it is capable of germinating in the spring or autumn and over wintering as a rosette [1,2,3]
The single preplant (PP) applicationprovided effective early control of the glyphosate resistant (GR) Canada fleabane 1 and 2 weeks after the POST application (WAA), 74% - 91% and 79% - 84%, respectively (Table 3). These levels of control are similar to Eubank et al [23] who determined that a preplant application of glyphosate plus 2,4-D ester (860 + 840 g∙ae∙ha−1) provided 80-88% control of GR Canada fleabane 2 WAA
Symptoms observed on the GR Canada fleabane due to the glyphosate DMA/2,4-D choline application included epinasty of the growing point, overall yellowing and stunting compared to the weedy control
Summary
Commonly known as Canada fleabane, horseweed or mare’s tail, is a facultative winter annual weed meaning it is capable of germinating in the spring or autumn and over wintering as a rosette [1,2,3]. Canada fleabane is not limited in autumn and spring germination, as it has been reported to germinate year round as long as the environmental conditions are adequate for germination and emergence [1,3,4,5]. This weed is difficult to control with one herbicide application due to its year round germination. GR crops supported the adoption of no-tillage practices, especially in soybean, allowing glyphosate to be the primary method of weed control replacing single and multiple tillage passes [10]. The overuse of glyphosate has increased the selection for the resistant weed biotypes which has led to GR populations [12]
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