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Mystery maladies hit rice

Mystery maladies are affecting Louisiana and Arkansas rice fields. While not suspected to be linked — nor a huge problem in either state — there are similarities. Rice farmers and researchers want answers.

“Not knowing what it is really bothers me,” says John Saichuk, Louisiana Extension rice specialist. “Maybe it's fear of the unknown. Finding an answer is certainly our goal. It does seem to be more widespread this year — maybe because of all the rain. Whatever the cause, we've had more calls on it.”

Last year, a farmer outside Stuttgart, Ark., called Ken Adams at a loss to explain a small patch of stunted, unhealthy rice. In turn, the Arkansas County Extension agent called Arkansas Extension plant pathologist Rick Cartwright and they checked the field together. They found the malady wasn't isolated in the field but widespread.

“And it's spreading even more,” says Adams. “Now, that farm has the problem in two fields. It's worse this year. It's tough to say how badly this will hurt yields. I don't think yields will be hurt by half. They will be hurt significantly, though.”

The plant injuries look “kind of like cold water rice, except it can cover 80 percent of the field,” says Chuck Wilson, Arkansas Extension rice specialist. “Plants will be yellow and stunted with small panicles. Sometimes plants have an orange cast to them with lower leaves dying off. If you pull up plants, the base of the stem is black, as are the roots. If you split the plant open, there's a fungus growing. Instead of the root crown being white, it's dark brown to black.”

There are few hard, fast rules for the disease. “Many of the affected fields have had Grandstand applied, but not always,” says Wilson. “My instinct says this is something that's been around for a while — a stunted panicle size after heading tells me the problem hit at or before mid-season.”

Saichuk hasn't found root crown rot in Louisiana's mystery fields. “That doesn't mean it hasn't occurred here, but we haven't found it. If I had to bet, I'd put my money on having a different problem than the one in Arkansas.”

In recent years, Louisiana has had several odd problems. At first, Saichuk believed all were associated. That's no longer the case.

“We began experiencing some die-back and poor fields in Cameron Parish. That was eventually identified as hydrogen sulfide toxicity. That's already in rice research literature. It just took us a while to diagnose it.”

Then, problems began to show up in Vermilion and Acadia parishes. Die-back was common in affected fields. In most cases, producers were able to drain fields to remedy the problem. This year, though, draining didn't always work.

“Symptoms are not cut-and-dried,” says Saichuk. “Usually, the problem shows up when the rice is flooded. The crop just begins to die. A farmer will notice an area of his field that was lush a couple of weeks ago has died or thinned out. It's an overall necrosis of the crop.

“The thing is, when looking at the roots, the typical hydrogen-sulfide toxicity symptoms are seen. We know this problem is associated with anaerobic conditions in the soil.”

Compounding the situation: this year, some Louisiana Clearfield 161 showed similar symptoms — usually following a second application of Newpath. “We believe that's a separate problem. But something set those plants up, making them sensitive to Newpath. It's odd because in research plots Newpath can be applied at exorbitant rates without injury to the plants. Clearly, something is going on out in these fields that's setting Clearfield up for yield losses.”

“Part of the problem in tackling this is we're getting calls at late boot/early heading,” says Wilson. “When we get into the field, the rice is already in bad shape. Next year, we must find some of these fields earlier in the season.”

A few farmers say they've noticed symptoms very early in the year. One farmer says his field was sick prior to a Grandstand application.

“We've also seen it in fields where Grandstand hasn't been applied,” says Wilson. “That suggests the product isn't to blame except, perhaps, for aggravating the problem.”

Causes have bedeviled researchers. The problems aren't very predictable and, thus far, have been resistant to duplication in test plots.

“The only predictability is if a farm or field has a history of it, it'll likely come back,” says Saichuk. “The thing that drives us a little crazy is it won't reappear in the same spot. One year, we set up an elaborate experiment where a farmer told us, ‘Yeah, it shows up right here every year without fail.’ We had electrodes out in the soil, all kinds of sensors. And the problem showed up about 100 yards away. So we were out a year's worth of extensive research.”

Research is ongoing in Arkansas as well. “Cartwright has isolated several organisms but nothing we can point at and say is causative,” says Wilson. “We can't isolate it. Many times, we can take affected plants out of the field, put them in fresh soil and water and they'll recover. It's very odd. We're still trying to find out if the fungus is the cause or an effect. My hunch is it's an effect, but we don't know anything for sure.”

Nothing has shown up in Arkansas' nutrient analysis. The problem has been found on silt loams and on clays. It's been seen as far north as Craighead County and as far south as DeShay County.

“You know,” says Wilson, “we're getting closer, but the truth is we're still in the dark about the exact cause of this.”


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