Clay Schaefer’s soybeans were performing perfectly last summer. Then the dreaded soybean rust blew to within five miles of his fields.

To spray a triazole or not? To him, it was a no-brainer decision. Yes.

It was the same this summer. And if Asian soybean rust (SBR) lingers in your area and your beans are pre-R6 in development, you, too, should think about it, says Glen Hartman, plant pathologist for USDA-ARS at the University of Illinois.

“It doesn’t seem to be jumping, just rolling up from the South to the North and slowing in movement as the season winds down,” says Hartman, “But if we see a jump from Arkansas to Minnesota, then we have some problems and explaining to do.”

Schaefer is an east-central Arkansas grower who decided it was worth about $15/acre treatment costs to prevent SBR from ruining his crop. “If I can save or possibly add even 1½ bu. of yield, I can pay for a triazole spraying,” says Schaefer, one of hundreds of Midsouth growers who have stared the fungus in the face the past two years.

Arkansas and Mississippi saw most soybean-producing counties showing signs of SBR last summer (2009). By fall, all of those states, as well as most of Louisiana and Alabama, were colored red on USDA’s IPM Pipeline map, which tracks SBR, soybean aphids and other disease and insect pressures. In Arkansas alone, 600,000 acres of soybeans were sprayed for SBR.

But the Corn Beltwasn’t completely immune to SBR. Missouri and Illinois saw the disease in soybean and kudzu fields. One confirmed area was near the Illinois-Missouri-Iowa border. In all, SBR was confirmed in 16 states and 576 counties last fall.

A similar situation is feared this year. In mid-summer 14 counties in far-south Texas, southern Alabama and Florida had confirmed SBR.

Schaefer was even more ready for SBR this year. He farms about 3,600 acres, half soybeans and half rice. The beans range from Group 4.7s to Group 5.3s. Some are no-till, some are bedded on 60-in. beds and some are conventionally tilled. All are 100% Roundup Ready.

“When Scott Monfort, University of Arkansas Extension pathologist, talked about SBR at a local meeting last August, we knew it was just south of us 5-6 miles away,” says Schaefer. “I had my consultant scout the Group 5s because the 4s were already beyond the R6 growth stage.

“I had already sprayed about one-third of the beans to prevent anthracnose and aerial web blight. So I had about 600 acres of Group 5 later-planted beans left standing unprotected. I decided to spray with 5 oz. of a triazole. Now, I can’t be sure that I stopped SBR, but I know I didn’t hurt myself.”

Jared Ford, his crop consultant, points out that Schaefer was protected, while some others saw SBR invasions. “And he ended up with better-quality beans than the neighbors had,” says Ford. “Others saw quality issues, white mold in the pods.”

Most Corn Belt areas see their beans approaching the R5 growth state in mid-August. If southern weather patterns are pushing SBR northward, be ready to spray a triazole, he says.

Many southern growers treat soybeans early for potential diseases. But most pathologists don’t recommend an early treatment simply to prevent any potential damage from SBR.

“Nine-dollar or higher beans make it a more attractive treatment to spray a strobilurin early and come back with a triazole if SBR threatens the crop,” says Schaefer.
You must follow the fungicide label. “Even though some research shows that soybeans can be rust-damaged in the R6 stage, most triazoles are not labeled for use beyond R5.”

August 2010