Burcucumber can be one of the most difficult weeds to manage in corn. It can emerge well into the growing season and its vines can spread up to 25 feet and twine around corn plants.
"It can drag down the corn and make it difficult to harvest, impacting yields," said Mark Loux, weed scientist for the Ohio Agricultural Research and Development Center.
Loux is in the middle of a two-year study to determine the most effective way to manage burcucumber in corn.
"While we previously had an idea of the relative effectiveness of various pre- and post-emergent herbicides, we weren't sure what would be the most effective combinations of herbicides and application timings to provide the most consistently effective late-season control," said Loux, who is also a weed science specialist for Ohio State University Extension. "Late-season emergence varies from year to year based on rainfall patterns and other factors, but when burcucumber emerges in big numbers after post-emergent herbicides have been applied, it can create a mess."
Loux's research compares the effectiveness of various residual pre- and post-emergent herbicides and the timing of their application. In 2010, the first year of the study, researchers applied herbicides Lexar, Corvus+atrazine and Harness Xtra at planting (pre-emergent) and early post-emergent, when corn was at the V2 (second-leaf) stage. These treatments were followed with various residual and non-residual post-emergent herbicides, including Callisto, Spirit and bromoxynil. Researchers tested different timings for the post-emergent herbicides and single and multiple applications.
One of the research sites in 2010 was non-GMO corn; several more are planned in 2011, including at least one with glyphosate-resistant corn, Loux said.
The study's 2010 findings included these observations:
* The Lexar and Corvus+atrazine were much more effective than the Harness Xtra for control of burcucumber between planting and the post-emergent application. Not only were there fewer burcucumber plants with the Lexar and Corvus+atrazine, but the weeds were small and had not started to vine at the time of the post application. Plants in the Harness Xtra treatments were much larger, and some had already extended tendrils to the corn plants by the time the post-emergent herbicides were applied.
* There appeared to be more effective control when the residual herbicides were applied at the early post-emergent stage instead of at planting, but this was much less important than the choice of residual herbicide. These results indicate that delaying the residual herbicide application until corn is at about the V2 stage could provide more effective control in mid-season and allow a more flexible application window for later treatment.
* 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.
"We expect that results with glyphosate will be similar to bromoxynil, since both herbicides lack residual activity," Loux said.
It didn't seem to make a difference if Callisto was applied on 20-inch or 37-inch corn, but, Loux added, it's possible that the later application could be more effective in a year when burcucumber emerges in great numbers in late June or July.
"We will hopefully know more about this after another year of research," he said.
Loux first reported findings from the study in the Crop Observation and Recommendation Network (CORN) newsletter, produced by Ohio State's Agronomics Crop Team, a multidisciplinary group of faculty members and educators with OSU Extension and OARDC. The newsletter is available online at http://corn.osu.edu , where readers can sign up for a free e-mail subscription.