* Choice of post-emergent herbicide was even more important than the choice of pre-emergent herbicide. Applying of Callisto at either 20- or 37-inch corn resulted in half the number of burcucumber plants at the end of the season compared with bromoxynil. More importantly, the Callisto resulted in a biomass (total above-ground growth) and burcucumber seed production that was about 97 percent lower than where bromoxynil was applied. "So, the potential for the burcucumber to twine around corn plants and create a mess was much lower with Callisto, as was the seed production," Loux said.
* Spirit provided control generally similar to Callisto. The end-of-season burcucumber population was higher with Spirit compared with Callisto, but the biomass and seed production were similar, so the Spirit prevented plants from producing substantial above-ground growth. The researchers saw similar levels of control when they applied bromoxynil twice at the post-emergent phase. However, they saw no improved control when they followed Callisto and Spirit applications with a late post-emergent (50-inch corn) application of bromoxynil.
* The researchers monitored burcucumber emergence throughout the season in several untreated areas. The majority of the weeds emerged in mid-June, but emergence started in early May and extended into early July. "In 2010, we did not observe the substantial emergence that can apparently occur in mid-summer, based on grower comments, so these results may overestimate the end-of-season effectiveness of the herbicide treatments we studied."
Although there's another year to the research project, Loux said a few things are already clear to him. First, effective burcucumber management in corn requires a combination of pre-emergent and post-emergent herbicide applications. Starting with a pre-emergent herbicide reduces the number and also the size of the weeds at the time of the post-emergent herbicide application. Herbicides capable of doing so include Lexar, Lumax, Corvus+atrazine and Balance+atrazine. "Any of these should be much more effective for early-season control in comparison to atrazine premix products," Loux said.
More importantly, it appears that the use of a post-emergent herbicide treatment with both foliar and residual activity on burcucumber may be the most vital component of a management program. Callisto or Spirit, both of which have residual activity on burcucumber, provided more effective end-of-season control than bromoxynil, unless the bromoxynil was applied twice.