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Sheath blight and smuts in Arkansas rice

Sheath blight and smuts are at the top of Arkansas’ major rice disease list. At the recent Arkansas’ Southeast Branch Station field day in Rohwer, Rick Cartwright spoke about how best to handle them.

With respect to sheath blight, all semi-dwarf long-grain varieties are susceptible. One that seems less so is Cheniere.

“I don’t know what the reason is, but with normal management, Cheniere seems to have fewer problems with sheath blight,” said the Arkansas Extension plant pathologist. “We still have to spray it, but it’s rated between Cocodrie and some of the taller varieties. There are always exceptions, but normally we can use fewer fungicides on Cheniere.”

Over the last few years, growers have learned the hard way that highly susceptible semi-dwarf long-grains need to be scouted closely for sheath blight from mid-season on.

“If you let sheath blight blow out of the top of those rices, you’ve lost 15 to 20 bushels you won’t get back. That means those varieties need earlier and more frequent scouting. They also potentially need to be treated earlier than taller varieties.”

Cartwright hasn’t seen any results from spraying hybrids with a fungicide.

“Some folks spray them a little. Frankly, I’ve yet to measure a yield response from a fungicide. That’s true in both commercial fields and my own plots.”

Summing up

Cartwright summed up his fungicide test work this way: if you have a long-time rice production field in a semi-dwarf long-grain (including Cocodrie, CL131 and Cybonnet), “we’re getting a benefits from a fungicide.

“Forty percent of the time taller varieties like Francis and Wells are sprayed, we see a benefit. That means such varieties need intense scouting and good decision making.”

Medium grains (Medark, Jupiter, Bengal) and hybrids in the tests almost never get a response from fungicides.

“Sometimes the medium grains will break even. That happens 10 percent of the time. On the hybrids, that percentage is much less — we may have broken even one time. On those varieties, just because you’ve got a lot of sheath blight low means nothing to yield. The disease has to get up higher in the plant to really do any damage.”

Further advice

What about Wells and smut?

“Wells isn’t one we’ve had particular trouble with in kernel smut. It’s one that is moderately susceptible.”

There are preventative compounds, though.

“Because we can’t scout for or predict the smuts, if you’re growing a susceptible variety in a field that normally turns your combines black, we recommend a fungicide treatment. That’s at least during the boot stages. So there are two things to consider: a susceptible variety along with a history of intense smut.”

If the main tillers in your field are in the swollen leaf stage but aren’t heading yet, Cartwright said 4 ounces of Tilt — or the equivalent of another product — per acre is a consistent treatment for smut.

“If you get any earlier than that — say, when the panicles are just about to start into boot — the 6 ounce rate seems to provide more consistency.

“Spray earlier than that and inconsistency sets in. We’ve used 8 ounces and 10 ounces up to a week after mid-season. But even those high rates will fail if applied really early. If I was going in before any boot formation, I’d use the highest rate and hope for the best. Most of the time, you’ll get activity — it just isn’t a definite.”

Editor’s note: to read an unabridged version of this story, see the Delta Farm Press tabloid.


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