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Wisconsin Agriculturist

Soybean rust found in Mississippi sentinel plot, Florida field

The latest incidence of Asian soybean rust in Mississippi was found in a Poplarville-area sentinel plot sponsored by the Mississippi Soybean Promotion Board.

Meanwhile, Extension soybean specialists and plant pathologists reported more findings of the disease in Georgia this afternoon. More rust was also confirmed in Alabama and Florida Thursday.

The infection level on the Group 5 soybeans found at the Poplarville, Miss., site was “less than half of 1 percent,” said Alan Blaine, Mississippi Extension soybean specialist on Friday morning.

Even so, “we’re telling farmers south of I-20 if they haven’t already made a fungicide application, they need to give one serious consideration. Rust appears to be spreading a little. However, we still don’t feel the innoculum is built up as much here as it appears to have in the Southeast. And prevailing winds look to be helping us.”

Following a precedent established with the infected George County plot in mid-July, the Poplarville plot “is being destroyed as we speak,” said Billy Moore, Mississippi Extension plant pathologist. “To keep any spores from getting to commercial fields that’s the approach we’re taking.”

Moore, the discoverer of both Mississippi rust occurrences, said the rust’s movement remains sluggish. “I still feel we’re in good shape. The innoculum level remains very low.

“Yesterday afternoon, after finding it in the sentinel plot, we went to a 140-acre bean field about seven miles away. We also checked fields in Wayne County – about 50 miles from the original find in the Lucedale sentinel plot. We could find nothing suspicious.

“Today, we just finished checking fields right on the Mississippi/Louisiana line. We’ve found nothing in that area either.”

Next week, Moore and colleagues will “have an intensive look at producer fields around Hazelhurst.”

Anyone who decides to use a fungicide “needs to be certain of what they’re using and why they’re using it,” said Blaine. “If you’re south of I-20 and haven’t made an application, go ahead and make one. But we’re not recommending anyone come back with a second application yet. We just don’t have the rust load to concern me enough to recommend that.”

The particulars of an application are different for every grower: the crop stage, the timing, the product and everything else must be considered. “We’re happy to work with anyone on those considerations,” said Blaine. “Just give us a call. And prior to making a fungicide application, check your insects. See if there are some pest populations you’re dealing with. If you are, a tank-mix may be in order.”

On Friday afternoon, rust was confirmed at two new sites in Georgia’s Laurens and Tift counties. Tift County has already had several incidences of rust. The rust in Laurens County is a first.

“In Laurens County, we found rust on a couple of leaves out of a 100-leaf sample on plants at R-5/R-6,” said Bob Kemerait, Georgia Extension plant pathologist. “But even with that small amount, there was definitely pustules and sporolation happening.”

Rust has quickened its march across the state’s coastal plain. “Laurens County is on the northern edge of the plain. This is further evidence coastal plain growers need to spray their crops with a fungicide.

“Laurens County is basically at the same latitude as rust sites in Effingham County and Auburn, Ala. Since that’s the case, we’re beginning to look harder at northern Georgia. Producers in north Georgia may not need to spray a fungicide immediately but they do need to be prepared to do so. I don’t think it will be too long before we find rust moving into their area.”

The Tift County rust was found near Chula on a private research farm’s beans at R-3. The sporolation from the site was much more pronounced than in Laurens County.

“Rust hasn’t taken over the field but there are a lot of leaves involved with many pustules. It’s a bit more dramatic than what we’ve seen before.”

The latest cases have led Kemerait to believe rust has reached a critical phase. “I think we’re now on the verge of an epidemic. Over the next few days, the weather is supposed to be rainy, and I suspect the rust is about to take off for the first time this year.”

The latest Florida finding marked the first time Asian soybean rust has been found in a commercial soybean field in that state. The discovery is in Hamilton County, on the north-central border with Georgia.

“The rust isn’t severe at all – from the central infection, the rust might have branched out a foot or two,” said David Wright, Florida Extension soybean specialist on Friday morning.

“The soybean field it was found in was chest-high and bushy. The beans were Group 5s in the R-1/R-2 stage, planted mid-May. My understanding is a scout with the Florida Division of Plant Industry found it. They’ve had scouts out looking for rust in beans and kudzu.”

Lately, Florida growing conditions have been excellent. Since the field’s canopy was so dense, “air wasn’t moving through the crop very well. That’s one reason infection was able to get going.”

Patches of rust have now been found across the Florida panhandle and Wright believes current weather conditions – daily showers and warm temperatures – will lead to even more. “It wouldn’t surprise me at all to find more rust over the next week or so. We’re set up for more infection.”

For that reason, “we’re recommending soybean producers in the early bloom stage use a fungicide with curative effects. If weather conditions remain this damp, another application may be needed in a couple of weeks.”

Wright asked producers to maintain good scouting. “Check five to 10 areas across a field because it’s so difficult to find. Scout a different area of the field every time. And be prepared to use a fungicide.”

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