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Arkansas rice diseases and varieties: 2005 in review

NEWPORT, Ark. -- Finding anything redeeming about Arkansas’ 2005 drought is a stretch. One possibility glass-half-full types might point to: with only a couple of caveats, rice diseases were taken off the boil.

“Sheath blight is a bit of an exception to that because it functions between the waterline and upper canopy,” said Rick Cartwright, Arkansas Extension plant pathologist at the Jackson County crop production meeting in Newport, Ark. “Once the rice canopy closes, a small ‘tent’ of humidity is constructed where the fungus can operate.”

Dry years keep the blight from completely blowing out the top and taking out heads. But it still does damage to foliage resulting in yield loss.

“So we had some rather severe sheath blight in 2005, especially in July when the state caught a few rains. The high temperatures also helped sheath blight out more than they did in 2004.”

Conversely, blast requires pre-leaf moisture to keep going in order to do well. So, compared to 2004, last year saw mild blast. That’s true even though “we had a lot of drought stress which normally provides neck blast with more potential.”

Recently, the blast race IE-1K has been keenly watched and worried over. Having developed on Banks, formerly a resistant variety, IE-1K has proven capable of overcoming resistance genes.

Since IE-1K has spread through northeast Arkansas, Cartwright has shifted Banks from the “resistant” camp to “moderately susceptible.” And the pathologist warns that in fields where IE-1K exists, Banks will be truly susceptible.

“We’ve got to keep that in mind when addressing blast. Last season, when we got concerned with IE-1K, we changed our recommendations a little.

“The blast fungus can travel on seed. That’s one way it gets into fields. With all the minimum tillage going on, it can also reside in crop residue.

“We’re trying to address that in our current recommendations. Between the annual seed-borne blast issue and the development of this new race, IE-1K, recommendations have changed. We’re now advising that producers monitor all varieties for this disease. All our resistance genes have been compromised by this fungus.”

Cartwright believes the moderately resistant/resistant varieties ratings remain “pretty stable.” But there are times, when conditions produce a “blasty” situation and producers need to keep an eye on “everything just to make sure something doesn’t sneak into the field.”

To help deal with blast, producers can turn to a new seed treatment fungicide, Dynasty. “It can do a very good job with stand establishment and also suppresses seed-borne blast. If you’re constantly having problems with blast — like in a river-bottom field — this could be a way to break up the disease cycle. It could hold back the disease until flood when you can get a better handle on it.”


The smuts were a bit more severe, but sporadic, in 2005. Export markets have complained, said Cartwright. “We’re going to have to try to do a good job on the smuts every year if we’re to continue exporting a lot of rice.”

Last season, the “Bengal disease” — bacterial panicle blight — was moderate although it was found on Francis for the first time. While there was no severe damage, it also concerns Cartwright the disease was found in a few fields on the Grand Prairie.

For smuts, boot stage is the best time to apply fungicides. “If you’re earlier than that, or in heading, activity will be lost. That’s being reiterated each year.

Variety quick hits

Spring: An early cultivar released by the University of Arkansas’ breeding program, Spring doesn’t have a great disease package. However, it’s very early and tends to outrun many diseases.

“It is very weak on stem rot, though. On low potassium soils in northeast Arkansas, we saw quite a few stem rot and lodging problems with it last year.”

Cheniere: As far as semi-dwarf long-grains, Cheniere has been a nice surprise. Out of the LSU breeding program, it’s a relative of Cocodrie.

“But it’s a better variety than Cocodrie — including in respect to diseases. Cheniere is moderately susceptible to sheath blight. We’ve been able to manage it, generally with lower rates of fungicides and later applications. In that respect, it’s much more like Wells than a semi-dwarf. It’s had a good run across the state.”

Clearfields: Both Clearfield 131 and 161 are very susceptible to sheath blight, a major disease. With these varieties, producers must be out in front of the disease in order to control it.

“131 is also very susceptible to straighthead, much like Cocodrie. If you’ve got a straighthead field, be very cautious about planting CL 131.”

Cartwright is frequently asked if 131 is an improvement over 161. “It doesn’t look like there’s a lot of difference. 131 is a different plant type — a little shorter, more erect. But sheath blight will hammer both of them. They’re also very similar in reaction to blast.”

On the flip-side, across many growing locations, there’s a 4-bushel to 5.5-bushel yield difference between the two. “What you don’t see is that out of the 16 locations, 131 had much higher yields than 161. But in three locations it was blasted, bringing the overall yield number down. It has higher yield potential — but keep it out of real trouble fields.”

Interestingly enough, even though 131 and 161 react similarly to sheath blight, yield losses were in the 30-plus bushel range where the best treatments were in place. The milling data suggests 131 — “even though it has less quality, in general, than 161” — in the presence of sheath blight and fungicides is more stable.

“It doesn’t take the hit that 161 can from sheath blight. It doesn’t seem to lose as much. Scout early and often with these two and apply a fungicide early, if needed.”

Trenasse: Trenasse is a very productive, very early semi-dwarf long-grain out of LSU. Unfortunately it has some major disease weaknesses. Sheath blight “can eat it up” and Trenasse is also very susceptible to straighthead. Cartwright has lost some plots of the variety to straighthead.

Cybonnet: “Cybonnet has been a pleasant surprise for us. Even though it’s very susceptible to sheath blight, like the old Cypress, it still has good blast resistance. It holds up better — even to IE-1K — than Banks, even though it’s somewhat susceptible. It also is resistant to all the other blast races.”

Cybonnet also has excellent milling quality and its yield potential is better than anticipated. Cartwright predicts Cybonnet, a semi-dwarf, “should get some play, especially in the state’s sandier ground.”

Jupiter: Another variety out of LSU, Jupiter was released several years ago. While resistant to bacterial panicle blight, there’s an ongoing debate about its small grain size. That concern will play out this year and “we’ll see if that slightly shorter grain size holds it back. Bengal and Medark both produce grain sizes that are acceptable. Looking at kernel weights, Jupiter is a bit lighter. I don’t know if that’s enough for buyers to reject it. But there is some concern and you should know that before planting a bunch of acreage in it.”


TAGS: Management
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