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Corn+Soybean Digest

Soybean Rust Problem In Late Fields

In the third week of September, with new sets of Midsouth counties and/or parishes frequently being added to the Asian soybean rust “confirmed” list, the disease is certainly worrisome for producers with late-planted soybean crops.

Many soybeans in central Arkansas’ Jackson County “are still a ways away from harvest,” says Randy Chlapecka, the county Extension staff chair for the University of Arkansas Division of Agriculture. “There are only a few fields ready. Most are still weeks away.”

Soybean rust was confirmed in Jackson County on Sept. 14.

“We still have some late-maturing, late-planted soybeans that are vulnerable to soybean rust. Those will probably need to be sprayed with a fungicide when the weather finally clears.”

Current wet conditions “are ideal for soybean rust,” says Jeremy Ross, Arkansas Extension soybean specialist. “Very few, if any, beans were sprayed (the week of Sept. 14). Here lately, we confirm rust in counties almost like clockwork. Pretty much the entire state has rust, now. As soon as it dries up the vulnerable beans will need to be sprayed.”

And it isn’t just soybean rust that’s shown up recently. Aerial blight, frogeye and other soybean diseases “were being picked up before the rust started to get going. These are really ideal conditions for nearly any disease.”

How much of the Arkansas crop is still in jeopardy due to the rust?

“It’s hard to say, for sure,” says Ross. “There’s a lot of the crop that’s very late. Most of the beans are starting to shut down. I believe USDA estimated we’re at 75% beginning to turn. Dropping leaves and turning yellow is around R7. So, there’s probably 20-25% of the crop that rust could cause premature defoliation or other problems.”

In neighboring Mississippi, “it’s very difficult” to go into a soybean field “and not find rust – especially in the Delta region,” says Trey Koger, Mississippi Extension soybean specialist. “Rust is pretty much everywhere.”

There have been some “isolated cases” where the malady has defoliated spots in fields. “The vast majority of those cases, however, didn’t see any yield drop because the crop was so mature.”

There has been one field in east Mississippi’s Noxubee County where rust “has caused some yield reduction,” says Koger. “But it’s difficult to say how much loss. It’s also difficult to say the loss was solely due to rust since there are other diseases in that field – charcoal rot, mainly.”

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