For much of the 2004 growing season, Arkansas' weather was mild and cloudy. That was good for crops but also good for disease reproduction, according to Rick Cartwright, Arkansas Extension plant pathologist. Diseases like rice blast — a foliar disease needing moisture and milder temperatures — were especially happy with the weather.
“A large percentage of our rice was affected by blast on the leaves,” said Cartwright, who spoke at a production meeting in Searcy, Ark. “We managed the neck blast pretty well. We had some wipeouts in certain fields, but nothing close (to the devastating potential of the early leaf blast).”
Sheath blight tended to be moderate. Clearfield 161 was the one variety hurt by it early in July.
“CL161, used for red rice control, is a very leafy semi-dwarf. Once it canopies over mid-season, sheath blight can blow up in it. Farmers need to be out in their fields before mid-season checking what sheath blight is doing. It may require a fungicide a little earlier than normal, but it can be controlled if you spray at the right time. If you let it blow out the top early, even if you spray and control it, you've already lost 15 to 20 bushels.”
Smut and “Bengal disease” (bacterial panicle blight) were mild. Even so, Cartwright warned that the chemical control option for Bengal disease “seems to have fizzled out. I don't think it will happen now.”
On the flip side, Louisiana State University has several resistant varieties in its program — one long-grain, one medium-grain — that appear to work well on the blight.
“We've tested their 2183 medium-grain for two years. It's showing resistance in our trials as well as theirs. In the future, that variety may be an alternative to Bengal. Because (bacterial panicle blight) is seed-borne and difficult to detect, we're doing seed detection work on Bengal. We're using a new machine we hope will help find it. If clean seed is planted, it probably won't be as big a problem.”
More on blast
It's important to make good choices on the front end. Plant the right varieties.
“If you get into the wrong situation — a susceptible variety in ideal conditions for disease — things can fall apart.”
But blast resistance in rice varieties isn't always cut-and-dried, warned Cartwright. “We turn out resistant varieties, and we base that claim on the fungi we know are out there. We put these varieties in a field and the resistance gene is a selection pressure on the fungi. The fungi respond by breeding races that try to overcome the resistance. This can take quite a while in certain crops, not so long in others.”
An example is IB49, which “took out” Newbonnet a few years ago. The IB49 blast race has been around since the 1980s and is the one most commonly found in the state's crop. Ahrent, Banks and Cybonnet all have a gene resistant to IB49.
Another race, IE-1K, can attack varieties resistant to IB49. Researchers have known about this race since 1993, but it remains rare.
“It was found first in Mississippi, and we've seen it sporadically since. In 2004, one field of Banks, a new variety, was damaged by this race in northeast Arkansas. Almost all the isolates we checked in 2004 were IB49.”
“Pi-ta” remains the best resistance gene available. “We'll continue to use it in varieties like Banks and Cybonnet. But we're going to move towards what we're doing with wheat. IE-1K has caused losses, so we're going to recommend that if you're on a blast-prone field, even with a resistant variety, you need to check it occasionally.”
Warnings and scouting
The blast fungus can survive in old straw. If you're farming sandy, blast-prone fields, it's a good idea to get rid of residue occasionally.
“Early planting also helps with blast. I'd plant those types of fields first. Blast fungus can be seed-borne. If you were to plant a bunch of affected seeds, it could jump to seedlings and begin bothering the crop early. While that can happen, environmental conditions really drive the disease.”
A 4-inch flood is important to suppress neck blast. Breaking up larger fields to irrigate more effectively can help with blast, said Cartwright.
For producers who plant early, a good time to monitor for leaf blast is between mid-June and mid-July. Once the plants begin to boot, many of the lower leaves will dry up and scouts might miss the disease.
“A new seed treatment being heavily promoted by Syngenta is called Dynasty. It contains the active ingredient in Quadris, a fungicide recommended against blast. The label suggests that at higher rates, Dynasty allows some seed-borne blast suppression. We don't have clear data on this yet, but if you're in a field with repeated blast troubles, you might want to check this product out. It doesn't give you season-long blast control, though — you still need to scout.”
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