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Mississippi: no uniform spraying recommendation for ASR

In the wake of Asian soybean rust having been discovered in southwest Mississippi on Aug. 1, Alan Blaine has some advice for soybean farmers in the state. “There are several issues I believe growers need to focus on,” says the Mississippi Extension soybean specialist.

Crop maturity. “Between 60 percent and 80 percent — probably in the upper range of that percentage — of our crop is home-free from rust. It’s that far along.”

Soybean harvest in the state began July 10.

“That isn’t necessarily good. But due to the prolonged, dry weather, that’s what we’ve been doing.”

Location. Every ASR find thus far is south of I-20. And it appears to be isolated to the southwest.

“Mississippi is almost uniformly hot and dry. The conditions we’ve had the last couple of days are absolutely not conducive for rust. The wind has been blowing out of the west at 95-plus degrees. That’s supposed to continue at least (into the second week of August).”

Fungicides. Don’t rush to make a fungicide application.

“Even if weather conditions become ideal for the disease, I believe ASR will show up sporadically. From what we’ve seen, the innoculum potential is extremely low. Couple that with hot weather and any ASR threat is further tamped down. And no moisture is forecast for the next few days, at least.”

Blaine and colleagues aren’t calling for any uniform spraying. Any application should be done on a “field-by-field basis. What have you done thus far in the season? What stage is the crop in? What are the current environmental conditions? What is the innoculum potential? All those things need to be answered.

“Don’t spray a fungicide until you at least talk to your county Extension agent and (chemical) dealer. I’ve been on the phone steady (since the ASR news broke). And I think, for the most part, growers are already doing that. Growers seem to be sitting tight and that’s the right approach.”

Mississippi has a problem much larger than ASR, says Blaine. “It’s called ‘dry weather.’ Even for those irrigating who have decent yield potential, this has been a very expensive crop. It’s going to be hard to make any money because pumping costs are so high.”

Blaine says growers should know the ASR found has been in very small amounts. To find the disease, the state’s ASR scout team (see, “searched for two hard days and these two small infections were all they could find. On his way back to Mississippi State (University) campus from the infected soybean field, (plant pathologist) Billy Moore said he probably had every leaf with rust in a Ziploc bag. That’s how small of an amount they found.”

The second find, on kudzu, was a bit larger in size — a few feet square. As with the soybean discovery, the infected kudzu was in a partially shaded area.

“The scout team traveled from the Vicksburg area to Yazoo City, across the bluff in the south Delta. They found nothing suspicious. So they went to the coast and came back up the eastern side of the state checking soybean fields all along the way. Again, they found nothing and these guys can find a needle in a haystack.”

Early in the week of Aug. 6-12, the scout team will make another tour of the state.

“What we’re trying to do is stay on the northern edge of any infection. We always want to know ASR’s northernmost location. Right now, we don’t believe it is any further north than the outskirts of Natchez. And what’s there isn’t much.”


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