The growing season's hot, dry weather means there's only a smattering of foliar diseases in Arkansas' rice crop. There is one exception, though: sheath blight.
“Sheath blight doesn't care much about the weather,” said Rick Cartwright, Arkansas Extension plant pathologist. “It's down in the water with a canopy over it so it's always got its own little greenhouse to work in.
“This year, we've had substantial sheath blight pressure. It's been very evident in some susceptible semi-dwarf varieties like Clearfield 161. Lots of calls have come in on that variety.”
While it isn't a no-show, blast - a regular menace to the crop - “hasn't gotten a major hold on us,” said Cartwright, who spoke at the Rice Research and Extension Center field day in Stuttgart, Ark., on Aug. 10. “This year, there haven't been any widespread problems. There are, however, some scattered fields with blast.”
Blast is a foe that must be confronted through genetics, said Cartwright. Over time, though, the blast fungus fights back.
“We try to keep it down, try to put resistance into varieties. But if you plant a lot of a certain gene, the fungus will find a way to overcome it. And given enough time, it will succeed.”
At the field day, Cartwright fielded several questions regarding blast.
“I don't understand all the molecular issues about how blast attacks a rice plant. But the basic principle is the same thing we see in many cropping systems. That is, when you put selection pressure on an organism, it will fight back. It's very similar to the selection pressure we put on weeds using so much glyphosate.”
In fields favorable for blast, producers normally plant varieties containing a strong resistance gene.
“That gene puts pressure on the blast fungus and says, ‘You can't come in. This may be where the food and lodging is, but this gene says you can't come in.’”
The fungus has to fight back and find a way inside the plant's defenses or die. Cartwright likens the process to a war.
“When you put that kind of selection pressure on a fungus, eventually it will find a few soldiers able to handle that resistance gene. Once those soldiers find a way in, the fungus will eat that variety up.”
Regarding other rice diseases, Cartwright warns that smut and panicle blight like hot years. “So we may see more heading disease problems than we had last year. That's something to watch for.”
Stem rot has also reared its “ugly head” in parts of the state. “Because of the increased inputs in growing rice, some producers decided to cut back some things, including potassium fertilizer. Stem rot has taken advantage of low potash soils.”
Most stem rot problems have occurred on lighter soils - silt loams and sandy loams with low native potassium fertility.
“When you have a soil that's inherently low in potassium, you have to fertilize every year.
“The high-yield varieties we're planting won't do well otherwise. If you miss out on that fertilizer, it can bite you. We've had some heavily damaged fields because of that.”
Prescribing a variety
An “amazing” number and mix of rice varieties are now available. And for those willing to do their homework, much data on those varieties can be accessed.
“There's enough information now where you can almost prescribe a variety to a certain field. None are perfect, but most of the varieties have a place they'll work well. We spend a lot of time figuring out where that is.
“I want to know, ‘In all the different environments we grow rice in Arkansas, what variety fits best in a specific field?’ If a farmer could figure that out, it would maximize yield and quality potential for a farm.”
Planting a variety or two across an entire farm means “they'll hit in some spots and miss others. The potential won't be reached.”
Matching a variety to a specific field may sound complicated, but it's really not, said Cartwright.
“An example of this could be a field with high-yield potential that isn't strong in sheath blight years. In that field, you could put a semi-dwarf like a Cybonnet or Cheniere.
“In high-yield potential fields prone to have more sheath blight but very little blast risk, Francis or Wells could fit.”
Cartwright touched on several specific varieties. Among them:
Banks has high-yield potential but also has leaf blast in some dry areas of Arkansas.
“Last year, a new race of blast attacked Banks. Because this new race can attack the main blast-resistant gene in our rice, it made us a little nervous.”
Cartwright currently has Trenasse, a variety out of Louisiana State University's breeding program, in his plots.
“It looks a bit weak on sheath blight, but it's still early. Hopefully that will translate into a positive for length of control - maybe we won't have to spray it with quite as much fungicide.”
A semi-dwarf long grain, Cheniere has impressed the plant pathologist.
“It appears more tolerant of or resistant to sheath blight than most of the semi-dwarves. Side-by-side, it's quite a bit more resistant than CL161, CL131 and Cybonnet. It's even more resistant than Cocodrie, which it's related to.”
A very early variety, Spring can “outrun a lot of problems if you plant it early enough. It's in the moderate range on most diseases.”
The main problem with the Clearfields - 161 and 131 - is sheath blight.
“By now, everyone knows that's the case. However, we can control sheath blight pretty easily with fungicides. So that susceptibility doesn't mean as much as it used to. Because of the problems with red rice in the state, Clearfield technology will be more and more important.”
Jupiter. A new variety out of LSU, Jupiter seems to have resistance to bacterial panicle blight.
“This variety is kind of a mystery because it's so new. On my test, though, it's done well against panicle blight. Time will tell as it's planted on more acres.”