Soybean rust may be a manageable disease, but getting effective fungicide coverage with the most efficient equipment and the least amount of cost may turn out to be a challenge.

Erdal Ozkan, an Ohio State University Extension agricultural engineer, said that 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. And because of the nature of the disease, such information is considered important.

“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, a researcher with Ohio State’s Ohio Agricultural Research and Development Center. “The most frequently asked question we get from farmers related to soybean rust control is how effectively should you apply fungicides to get the maximum benefit.”

In response to this inquiry, Ohio State agricultural engineers and plant pathologists, along with U.S. Department of Agriculture researchers based at OARDC, have launched a series of studies to determine which types of nozzles and/or sprayers provide the best fungicide coverage with the least amount of additional costs and the most environmentally friendly results. The data will be presented at Farm Science Review, being held Sept. 20-22 at Molly Caren Agricultural Center in London, Ohio.

“We are looking at several options. One is using a conventional sprayer and just changing out a variety of nozzles. Another is looking at air-assisted sprayers, more expensive kinds of equipment. And a third is looking at sprayer quality in regards to droplet size,” said Ozkan. “We want to determine what are the best options in terms of nozzle type, range of droplet size, nozzle set-up and sprayer set-up.”

Researchers are analyzing four types of nozzles to determine which type (cone or flat-fan, for example) would work most efficiently.

Treatments also include using air-assisted sprayers — equipment that uses air to spread open the plant canopy before applying fungicides. One sprayer is in the experimental stages, developed by Ohio State agricultural engineers to provide growers with a less-expensive alternative to air-assisted sprayers currently on the market.

“The equipment is called a mechanical canopy opener and works like an air-assisted sprayer. A horizontal bar retrofitted to a conventional sprayer a foot below and a foot behind the boom pushes the canopy forward opening up a space for spray droplets to reach the lower canopy,” said Ozkan. “Air-assisted equipment can cost an additional $10,000 to $15,000 for a grower, but this equipment could only be about a $300 option that gives similar results.”

A third aspect of the research is analyzing spray quality — whether medium, fine or coarse droplets provide the most effective coverage.

“Typically for soybean rust the recommended spray quality is fine to medium. Well, is the classification fine or medium? Or is it coarse?” said Ozkan. “The smaller the droplets, the higher risk of spray drift, so pinpointing droplet classification is important. Altogether, we are looking at 10 different treatments involving several conventional nozzle types operating at different conditions, some new sprayers, and different spray quality classifications. “

The treatments, being conducting in OARDC and OSU/ATI soybean plots in Wooster, will be replicated four times and evaluated using three methods:

• Water sensitive paper placed on metal target holders at heights of medium and lower parts of the canopy. The paper turns from yellow to blue when it gets wet. The more blue the paper, the more fungicide coverage the plant received. The coverage expressed in percentages will be determined by using image analysis software.

• The actual amount of fungicide, in micrograms, that was deposited on the leaves and stems at different heights.

• Florescent tracers added to the mixture before application. Certain target areas will be equipped with metal plates and after treatment the plates will be analyzed to determine the amount of tracer found on the plates.

“I don’t think anyone in the U.S. has done this kind of extensive research in determining the effectives of fungicide applications on soybean plants for soybean rust,” said Ozkan. “Hopefully it will give us more precise management recommendations to farmers.”

The project is being supported by Ohio State University Extension, OARDC, various equipment and chemical companies, and the Ohio Soybean Council through soybean check-off funds.

Farm Science Review is sponsored by Ohio State University’s College of Food, Agricultural, and Environmental Sciences, OSU Extension and the Ohio Agricultural Research and Development Center. Tickets are $8 at the gate or $5 in advance when purchased from OSU Extension county offices or agribusinesses. Children 5 and younger are admitted free. Hours are 8 a.m. to 5 p.m. Sept 20-21 and 8 a.m. to 4 p.m. Sept. 22.