Asian soybean rust has been found in extreme southeast Arkansas. Hard on the heels of the latest discovery in Mississippi (see Soybean rust in Mississippi), the Arkansas find is of low severity and has not necessitated a blanket recommendation for fungicide applications.
“Rust was found south of Lake Village in Chicot County around Lakeport,” said Scott Monfort, Arkansas Extension plant pathologist, shortly after the disease confirmation. “It’s very close to the Mississippi River on some R-7 soybeans — at full maturity. It isn’t unusual to find rust on mature beans. Since the field has reached maturity the rust won’t harm the crop whatsoever.”
Of the 100 leaves collected in the field, only one leaf was found to have the disease. And on that leaf “there were only a couple of pustules — less than 1 percent severity. That’s a very, very low incidence.”
Many surrounding Lakeport fields were also checked and found to be clean. “That’s one reason we’re holding off a fungicide recommendation. We’ll revisit the area and see if (the disease) is building up or acting differently. There’s no need for a panic, right now.”
Interestingly, the Arkansas and Mississippi finds are less than 50 miles apart and almost on the same latitude.
How many acres — and how vulnerable — is Arkansas’ late-planted soybean crop?
“We probably have 3.4 million to 3.5 million acres of soybeans, total in the state. The estimate is that at least 1 million acres of those — probably 1.5 million acres, actually — are late-planted.
“That means at least a third of our crop could be damaged by rust if it builds up and moves north. Right now, there haven’t been a lot of good, strong winds to push the rust spores north, though. Winds have largely been moving towards the southeast.”
In 2008, soybean rust “came in late and hung around without doing very much. The weather kept it in check. This year, we want to wait a bit and see if the rust is more aggressive before growers start putting out a bunch of fungicides.”
Monfort encourages growers “not to get in a hurry and not to worry about soybean rust. Right now, everyone needs to continue to manage fields for the other diseases we know are out there: mainly frogeye, aerial blight and anthracnose.”
If those diseases are in the field, “go ahead and treat with the typical strobilurin fungicide. If this rust begins to develop and move — and we’ll be quick to let everyone know — it may be necessary to change over to triazoles. Right now, don’t focus on soybean rust and ignore the diseases we have on hand.”
Monfort requested that samples pulled from fields with suspected soybean rust be sent to diagnostic labs in either Monticello or Lonoke.