COLUMBUS, Ohio -- When it comes to managing soybean rust with fungicides, a number of application options that provide effective coverage are available to growers.
According to the results of an Ohio State University study conducted at the Ohio Agricultural Research and Development Center in Wooster, Ohio, a mix of sprayers and nozzles under certain production situations can provide relatively equal coverage of fungicide on soybean plants.
"The goal of the study was to determine which spray equipment would be the most effective against soybean rust," said Erdal Ozkan, an Ohio State University Extension agricultural engineer and one of the researchers of the project. The research team included plant pathologists from Ohio State, and engineers from the U.S. Department of Agriculture ARS Application Technology Research Unit in Wooster. Soybean rust has yet to be discovered in Ohio, but researchers strive to prepare growers for its potential arrival.
Findings from the research include:
• When using conventional sprayers, nozzles that provide medium spray quality, rather than fine or coarse, tend to provide a better penetration of droplets inside the plant canopy and better leaf coverage.
• Spray hitting the target from two different angles may produce better coverage if the canopy is not dense. But in dense canopy conditions, flat-fan nozzles with a single spray pattern producing medium quality spray tend to provide a better penetration of droplets inside the canopy.
• Air-assisted sprayers did a better job with penetration of droplets and spray coverage than a conventional sprayer.
• Using a mechanical canopy opener, conventional sprayers may provide coverage and penetration nearly as good as those from air-assisted sprayers. However, the canopy opener will not be effective in reducing spray drift, which is achieved using air-assisted sprayers.
• At 15 gallons per acre and seven miles per hour, and under dense canopy conditions, flat-fan nozzles provided better coverage and penetration into the canopy than hollow cone nozzles.
The results of the research were based on droplet coverage and deposition on a variety of artificial targets -- water sensitive paper and metal plates -- attached to a stake and placed inside the soybean plants in four replicated areas 50 feet wide and 150 feet long.
Nine application setups were tested in the research, involving three types of sprayers (air-assisted, AirJet, boom sprayer and boom sprayer with canopy opener), four nozzle types (hollow cone, flat-fan, TwinJet and Turbo TeeJet) and three types of spray quality (fine, medium and coarse). A detailed report on this study can be obtained from the following Web site: http://fabe.osu.edu/FACULTY/Report_Rust_study_2005.pdf
"We analyzed three ways to achieve our objectives. One way was to directly measure the efficacy of rust fungicides applied to soybean plants. Another was to use artificial targets implanted into the soybean canopy. And the third was to measure the amount of fungicide deposits on the leaves and stems of the soybean plant," said Ozkan, who also holds an OARDC research appointment. "Obviously, the first option was not available to us because luckily soybean rust didn't show up in Ohio. And we only have part of the data analyzed regarding fungicide deposits on soybean leaves and stems, although preliminary data is showing similar application results as those achieved using the artificial targets."
Data regarding fungicide deposits on soybean leaves and stems is expected to be completed by May.
Ozkan said that knowing which spray application is most effective in controlling soybean rust important, given the nature of the disease.
"The disease starts from the lower part of the canopy and progresses toward the top. And by the time rust would arrive, say in Ohio, soybean plants may be in advanced growth stages, sometimes three to four feet tall with good canopy coverage. Penetrating the lower part of the canopy with applications is very challenging," said Ozkan. "Despite the wide variety of fungicides available to control soybean rust, fungicide labels fail to clearly specify the type of application equipment or setup that would provide the best coverage."
The spray application recommendations are not limited to soybean rust, however. Ozkan said they are also applicable for managing soybean aphid or other soybean diseases, such as white mold, that exhibit similar growth characteristics to soybean rust.
Funding for the research was provided by the Ohio Soybean Council through soybean check-off, Ohio State University Extension, OARDC, USDA-ARS, BASF Corporation, Corn and Soybean Digest Magazine, Gregson Technologies, Jacto, Inc., Spraying Systems Co., and Unverferth Equipment Co.