Rice Farming

Newer fungicides are giving rice growers greater control options against sheath blight and blast in their fields, but experts say timing is critical for applications to successfully combat the key diseases. Apply too early and fungicides will not provide control throughout critical growth stages; apply too late and growers will miss their protective window.

Recent registrations of newer fungicides have expanded the options for rice producers to reach a broader spectrum of diseases, including both sheath blight and blast. Moncut 70DF, a long-time sheath blight fungicide, is now available in an improved formulation. Quadris 2.08SC, an industry standard from Syngenta Crop Protection containing azoxystrobin, has activity on both sheath blight and blast. Now the industry has registration for Gem and Stratego from Bayer CropScience.

Both Gem and Stratego are based on a new strobilurin chemistry called trifloxystrobin, which provides defense against sheath blight and enhanced protection against blast. Gem is straight trifloxystrobin. Stratego is a premix formulation of trifloxystrobin and propiconazole, the active ingredient in Tilt, which broadens the control spectrum to include smuts while also providing a resistance management rotational tool.

“Having newer fungicides, growers now can consistently get good economic returns on fungicide applications when disease is present and exceeds treatment thresholds,” says Don Groth, a plant pathologist with Louisiana State University. “We are seeing consistent benefits in yield, milling and less lodging. And in the Gulf region, farmers who use fungicides in their first crop regularly get thicker stands in their ratoon crop.”

Timing is critical
While the fit for each of these fungicides will depend largely on economics, variety susceptibility, field history and disease spectrum in the field, Groth says timing is the key for successful sheath blight and blast management no matter which product a grower selects.

“These products are only as good as your timely applications,” Groth says. “Timing is critical for disease control, especially blast, because you only have a five- to 10-day window to get something on there to do any good.”

While experts recommend two applications to control blast, with margins as they are, many growers rely on a single fungicide application to control sheath blight, blast or both, depending on pressures in their field. As a result, Groth says, it’s important to scout carefully and then time applications to coincide with the plant stage at which fungicides will have their highest effect.

“Ninety percent of our fungicides are going to be a one-shot market,” Groth says. “Rarely is a farmer going to put out two applications, so you want to hit the single best timing.”

Sheath blight
For sheath blight, Groth suggests growers begin scouting their fields at mid-tillering, examining the water line for oval lesions that turn tan to light brown and develop up the plant in a snake-skin pattern. Growers should check for sheath blight every 10 to 15 paces in the field, and consider a spray when 30 percent of the sites show signs of sheath blight.

For optimum sheath blight control, growers should apply a boot application of Quadris, Gem, Stratego or Moncut at the 2- to 4-inch panicle stage to protect plants through heading and early grain filling.

For growers relying on degree-day software models, such as the DD-50 Rice Management Program, applications for sheath blight for most varieties should be timed 10 to 14 days after half-inch internode elongation, according to pathologist Rick Cartwright of the University of Arkansas. The DD-50 program provides sheath blight scouting and treatment periods for each variety, based on degree days, variety and date of emergence.

“It’s the same timing, we just word it a little different,” Cartwright says. “It still amounts to an early boot application. The only exception to this is where a highly susceptible semi-dwarf long-grain variety gets into trouble early. We recommend that growers scout the new Clearfield CL 161 variety early and treat prior to boot if sheath blight is aggressive.”

Blast
Monitoring for blast also begins at mid-tillering, though there is no definitive monitoring system for blast established at critical stages of the disease. Leaf blast, characterized by diamond-shaped lesions on leaves, will not necessarily affect yield, but is an inoculum source for impending neck blast problems and an indication that treatment may be necessary, depending on history and variety susceptibility.

“Leaf blast is the warning sign. That, and if you have blast every year or if your neighbor has it, and you have a susceptible variety you need to get a preventative treatment out there,” Groth says.

Protect plant from blast
With blast, Groth says, it’s important to time applications at heading when about 50 percent to 70 percent of the heads are emerging from the boot, but are not yet fully exposed. Blast control requires direct contact with the head prior to infection because today’s fungicides offer little kickback or curative activity once the neck or panicle becomes infected.

“Blast is mostly a preventative type fungicide situation. We have no decision thresholds,” Cartwright says. “If conditions are favorable and you have found leaf blast in the field and have susceptible varieties, you should consider using a preventative fungicide application.”

Cartwright says the traditional recommendation has been for growers with susceptible varieties and favorable conditions to consider two applications to control blast, the first at 5 percent to 10 percent heading, when the panicle tips in main tillers are just coming out of the boot sheath. A second application comes about a week later when 75 percent to 90 percent of the panicle length has emerged from the boot.

“If you choose to do one application, you kind of split that timing,” Cartwright says. “If you were going to attempt to use one application, it would be when about 50 percent of the panicle length has emerged from the boot on the main tillers but the bottom halves of the panicles are still down in the boot.”

A matter of balance
Growers who have both sheath blight and blast and are considering a single application to control both diseases will likely have to delay sheath blight applications to capture the short window of control for blast, Groth says.

“If you are trying to control both diseases, it’s best to take a small hit on sheath blight, let it continue to develop and use Quadris or Gem at heading to control blast,” Groth says. “If I’m a grower in that scenario, I know I’m going to let sheath blight develop more than I want to, but I need to let it go so I can get the right timing for blast.”

Tilt and Moncut do not provide activity against blast. And while Stratego has blast control activity, it cannot be applied at the proper timing because the propiconazole cannot be applied to exposed heads. Groth suggests applying a full rate of Gem or Quadris for blast control, particularly under the single-application scenario.

Today’s selection of fungicides helps provide that flexibility and should also help farmers justify the expense of a fungicide spray, even in the current market. While fungicides may not directly improve returns, they will almost certainly help protect the farmer’s investment under disease pressures, Groth says.

“You probably have four or five hundred dollars per acre in that field,” he says. “If you’ve gone to that expense, then you need to spend $15 to $30 more per acre to protect it.”

For questions or comments, contact Rice Farming editor Vicky Boyd at (209) 571-0414 or vlboyd@att.net.

LOUISIANA RICE VARIETY REACTIONS TO DISEASE, DISORDERS AND INSECTS

R—Resistant
MR—Moderately resistant

MS—Moderately susceptible
S—Susceptible

VS— Very susceptible

	Blast	Sheath Blight	Narrow Brown Leaf Spot	Brown Leaf Spot	Leaf Smut	Straight- head	Rice Water Weevil Larvae	Rice Stink Bug
LONG GRAIN:
Ahrent	R	S	S	MS	S	MR	S	S
CL161	S	S	MS	MS	MS	MR	S	S
CL121	S	S	MR	MS	MS	MS	S	S
CL141	VS	S	S	MS	S	S	S	S
Cocodrie	MS	VS	MR	MR	MS	S	S	S
Cypress	S	S	MR	MR	MS	MR	S	S
Della	S	MS	MR	S	MS	S	S	S
Dellrose	S	S	MR	S	MS	MR	S	S
Dixiebelle	MS	S	MR	MS	MR	VS	S	S
Drew	MR	MS	MR	MR	MR	MS	S	S
Francis	S	MS	MR	MS	MS	MR	S	S
Jackson	S	S	MR	MS	MR	MR	S	S
Jasmine 85	R	R	MS-S	R	R	VS	S	S
Jefferson	MS	S	MR	MR	MR	MS	S	S
LaGrue	VS	MS	R-MR	R	R	S	S	S
Lemont	S	VS	MS-S	S	S	MR	S	S
Maybelle	VS	VS	S	S	S	MR	S	S
Priscilla	MS	MS	MR	MR	MR	MS	S	S
Saber	R	S	R	MR	MR	R	S	S
TORO-2	R	MS-S	MR-MS	MS	MR-MS	VS	S	S
Wells	S	MS	R	MR	MS	MR	S	S
XL6	R	MR	R	MS	R	VS	S	S
XL7	R	MS	R	S	R	MR	S	S
XL8	R	MS	R	S	R	MR	S	S
MEDIUM GRAIN:
Bengal	S	MS	MS	MR	MS	VS	VS	VS
Earl	MR	MS	R	MS	MR	VS	VS	S
Mars	S	MS	MS	MR	MS	VS	VS	S
Rico 1	S	MS	S	MS	MS	MR	S	S
Saturn	MR	MS-S	MS	S	S	S	S	S

* Varieties labeled S or VS for a given disease may be severely damaged under conditions favoring disease development.
Information courtesy of Don Groth, professor at Louisiana State University AgCenter and Louisiana Cooperative Extension Service.

ARKANSAS RICE VARIETY REACTIONS TO DISEASE AND DISORDERS

R—Resistant
MR—Moderately resistant

MS—Moderately susceptible
S—Susceptible

VS— Very susceptible

	Sheath Blight	Blast	Stem Rot	Kernel Smut	False Smut	Brown Spot	Straight- head
AB1542	MS	MS	MS	MR	MR	R	VS
Ahrent	MS	R	S	MS	S	S	S
Alan	MS	S	VS	S	-	R	MS
Bengal	MS	S	VS	MS	MR	VS	VS
CL121	VS	MS	S	S	MS	MR	S
CL141	MS	VS	S	S	MS	R	S
CL161	VS	MS	S	S	S	R	S
Cocodrie	VS	MS	S	VS	S	R	VS
Cypress	VS	MS	MS	S	S	R	MS
Dellmont	VS	MR	MS	R	-	R	MS
Dellrose	VS	MR	MS	-	-	MS	MS
Dixiebelle	VS	MR	S	-	-	R	MS
Drew	MS	R	MS	MS	S	S	MS
Earl2	MS	MS	MS	MS	MR	R	MS
Francis	MS	S	S	VS	S	R	MS
Jackson	MS	S	S	S	-	R	MR
Jefferson	MS	S	MS	S	MR	R	MR
Katy	MS	R	MS	R	MS	R	S
Kaybonnet	MS	R	MS	MS	S	S	S
Koshihikari	MS	MR	S	R	MR	MR	-
LaGrue	MS	S	MS	VS	S	R	MS
Lemont	VS	MR	MS	R	MS	R	MS
M-2022	MS	VS	MS	VS	MR	S	S
Madison	VS	R	MS	R	MS	R	MS
Mars	MS	MS	MS	R	-	S	VS
Maybelle	VS	S	S	S	-	R	MR
Millie	MS	MS	MS	MR	-	R	S
Newbonnet	MS	VS	S	VS	S	R	MR
Priscilla	MS	S	MS	S	S	R	MR
Saber	MS	R	S	S	MR	R	MS
Wells	MS	S	S	MS	S	R	MS
RiceTex XL6 Hybrid	MR	R	S	MS	MS	R	VS
RiceTec XL7 Hybrid	MS	R	S	MS	MR	R	MS
RiceTec XL8 Hybrid	MS	R	S	MS	MR	R	MS
Clearfield XL8 Hybrid	MS	R	S	MS	MR	R	MS
RiceTec XP707* Hybrid	MS	R	S	MR	MR	R	-
RiceTec XP710* Hybrid	MR	R	MS	MR	MR	R	-

1 Not recommended for Arkansas due to extreme susceptibility to rice blast.
Information courtesy of Rick Cartwright, Extension Plant Pathologist for the University of Arkansas Cooperative Extension Service, and Fleet Lee, professor at the Rice Research and Extension Center near Stuttgart, Ark.