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Corn+Soybean Digest

Sentinel plots ready to stand up and be scouted

Soybeans in the unifoliate -- or one leaf -- stage of development peak through the soil on grower Tom Weiler's Mt. Gilead, Ohio, farm.

Seeded on April 11, the beans are among the first planted in Ohio. They serve a specific purpose -- to aid in the early detection of soybean rust, if it shows up.

Weiler's 20 acres of soybeans are among 45 sentinel plots in Ohio designed to be the first line of defense in identifying the presence of rust. The sentinel plots are part of a nationwide effort in preventing the disease. All soybean-producing states in the country have at least 10 sentinel plots.

"Ohio has been pretty aggressive with the number of sentinel plots because of the dedication of the Extension agents," says Dennis Mills, an Ohio State University plant pathology program specialist. "We first started out with 30, and agents just kept showing up for the training. They've been great in terms of volunteering to monitor fields."

Soybean rust is an aggressive fungus similar to the rust fungi that causes wheat leaf rust and corn leaf rust. It is caused by either of two fungal species, Phakopsora pachyrhizi, also known as the Asian species, and Phakopsora meibomiae, the New World species.

The Asian species, the one found in the U.S., is the more aggressive of the two species, causing more damage to soybean plants. The disease was identified in eight states last year and all eyes are on this year's crop to see where the disease will progress next.

Steve Ruhl, Ohio State Extension Educator for Morrow County is responsible for watching Weiler's sentinel plot. He has schooled the grower, who has raised corn, soybeans and wheat for nearly 40 years, on how often to evaluate plants in the field and what to look for regarding disease symptoms.

"I really didn't have a say in the matter. Steve just sort of told me that part of my acreage would become a sentinel plot," says Weiler, who has had a working relationship with Ruhl for more than 20 years. "It has worked out well though, as I'm on the farm every day. Extension needs people who are dedicated enough to get out and check their fields."

Evaluating a soybean leaf is one thing, but to be able to detect an abnormality and identify soybean rust early enough for fungicides to be effective is another. And therein lies the biggest challenge for growers participating in the program.

"The main thing is identifying rust early. It looks identical to Septoria brown spot in its early stages, so it's going to be a challenge," says Tina Lust, a grower in Marion, Ohio, and a seed dealer for Midwest Seed Genetics.

Lust is monitoring a sentinel plot on her farm -- seven acres of soybeans planted on April 16. She has had a working relationship with Ohio State plant pathologist Anne Dorrance for several years on Phytophthora root rot research.

"Extension has been really good about teaching us to be some of the first detectors of the disease," Lust says. "We have been trained to scout plants once or twice a week in a 50-by-50-ft. area, and spend at least an hour and a half per visit.

"Once the disease is detected in Ohio, we then scout our fields every three days. The goal is to detect inoculation as early as possible. Once spores germinate, the disease has progressed and there isn't much time to get on spray applications,"

Such a short time window is throwing some growers into what Ruhl calls "panic mode."

"I've spoken with some growers who have already bought their preventive fungicides. If rust were to be detected in the state, they are planning on spraying as soon as it's reported," Ruhl says. "We recommend that growers just wait. Timing is everything and it can get expensive to spray several times if the initial spray ends up being too early and ineffective."

Weiler and Lust are taking that advice and waiting to see what happens.

Soybean plants in 37 of the 45 sentinel plots in Ohio already have emerged.

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