Common dandelion has developed into a troublesome agronomic weed for no-tillage corn and soybean producers in Michigan and throughout the north central region of the United States. Field experiments were conducted on established populations of common dandelion in 2001 to 2002 and 2002 to 2003 to evaluate the effect of preplant and sequential herbicide applications on established populations of common dandelion. Preplant treatments of glyphosate or 2,4-D ester were applied early fall, late fall, early spring, and late spring. For both glyphosate and 2,4-D ester, the fall applications were more effective than the spring applications. Glyphosate at 840 gae/ha was more effective than 2,4-D ester at 1,120 gae/ha at each application timing. A single application of glyphosate or 2,4-D ester applied either in the fall or spring did not provide season-long control of common dandelion. Sequential treatments of glyphosate following preplant applications of either glyphosate or 2,4-D ester provided season-long control of common dandelion.

Common dandelion has developed into a troublesome agronomic weed for no-tillage corn producers. A postemergence herbicide application is often required to reduce common dandelion competition. Field experiments were conducted in 2002 and 2003 to evaluate 22 postemergence herbicide treatments for efficacy on established populations of common dandelion in no-tillage corn. All herbicides were applied to five- to six-collar corn at registered rates with typical adjuvants. At 28 d after treatment (DAT) the most effective treatments included glufosinate and mesotrione providing at least 76% control of common dandelion. All other herbicide treatments provided less than 40% common dandelion control 28 DAT. Common dandelion control was evaluated 56 DAT when regrowth of treated plants was observed for some herbicide treatments. AT 56 DAT, dicamba + diflufenzopyr was the most effective treatment, providing 83% control of common dandelion. In 2002, all herbicide treatments, with the exception of flumiclorac, resulted in corn yields greater than the nontreated.

Integration of two or more methods in a weed control strategy may produce a positive interaction. In this study, sequential applications of sublethal rates of 2,4-D and the plant pathogen Sclerotinia minor were assessed for integrated control of common dandelion. S. minor was prepared as a granular treatment of fungal-colonized barley grits. Treatments of 2,4-D (25 or 50% of the recommended field rate) and S. minor treatments (20, 40, or 60 g m–2 rate) were applied alone or sequentially with a 3 wk interval. Fourteen days after inoculation (DAI), sequential applications of either rate of 2,4-D with 40 or 60 g m–2 of S. minor caused greater damage than either treatment alone (P = 0.05). By 21 and 28 DAI, control from 60 g m–2 of S. minor alone was equivalent to any of the sequential treatments (P = 0.05). At all assessment times, the combination of either rate of 2,4-D and 20 or 40 g m–2 of S. minor caused damage equivalent to or greater than that caused by 60 g m–2 of S. minor alone (P = 0.05). According to Colby's test for interactions, 19 of 24 assessments of the sequential treatments were synergistic. Therefore, sequential treatments of sublethal rates of 2,4-D and S. minor can interact positively to increase damage. This synergistic interaction may reduce the rate of either component required for adequate levels of control, possibly decreasing the cost or volume of use of herbicides in traditional weed control strategies.