Rice Farming

A collection of highly effective fungicides has given rice growers new confidence in controlling diseases, such as blast and sheath blight. But experts say an economical disease management program begins with variety and field selection and incorporates careful agronomic management in addition to well-timed fungicide applications.

“An integrated approach means looking at each field, putting the right variety in with the right management practices and using inputs correctly,” says Rick Cartwright, Extension plant pathologist with the University of Arkansas Division of Agriculture. “If you do that, the whole farm enjoys maximum profit. An integrated approach is where the farmer can make more money, even if it is a little more work.”

According to Don Groth, a plant pathology professor at Louisiana State University in Crowley, an integrated disease management program that will maximize yield potential and profit should incorporate the following components:

• Field and variety selection,
• Planting timing,
• Seeding rate,
• Water management,
• Proper fertility,
• Regular scouting and
• Fungicides if necessary.

Field and variety
“An integrated program starts before a grower has even planted a grain of rice,” Groth says. “The first important thing is field selection, because there are certain characteristics of the field that expose it to various diseases.”

A field with a history of sheath blight in rice, bad aerial blight in soybeans the previous season or where growers are following rice on rice will be at an elevated risk for sheath blight. Additionally, fields on light textured soils, where the flood cannot be well-maintained, or where trees or other factors are reducing air movement through the field will be more susceptible to blast. In those situations, Groth says it is important to plant a less-susceptible variety that will provide added protection against disease development.

“Your variety selection must be matched to the field. You want to put your best sheath blight material on sheath blight ground and your best blast-resistant varieties on blast ground,” he says.

Agronomic approach
Growers should avoid planting extremely early or extremely late, and also manage inputs, such as nitrogen and seeding rates, to avoid lush canopy conditions that can exacerbate diseases. Groth says to plant for a targeted seeding rate of 70 to 90 pounds per acre for drill-seeded and 125 pounds per acre for water-seeded rice, depending on seed size. In addition, apply enough nitrogen, based on variety and soil type, to realize maximum yield potential while not aggravating the disease potential.

Water management is the most critical component to minimizing the incidence of blast. Especially with newer, more susceptible varieties, researchers have discovered that maintaining a good flood will significantly reduce incidence of blast.

“Water management is a very critical thing in trying to grow these blast susceptible varieties,” says Fleet Lee, a plant pathologist at the University of Arkansas’s Rice Research and Extension Center near Stuttgart, Ark. “If a grower is not in a position to manage his water and fertility with LaGrue, Wells and now Frances, for instance, he better be very careful with it.”

Lee’s research has shown that maintaining a consistent flood 3 to 4 inches deep creates anaerobic conditions that affect the metabolism of the rice plant, making it less susceptible to rice blast. The oxygen stress actually forces the rice plant to produce ethylene, which somehow builds resistance in the plant. And Lee says the depth and duration of the flood correlates to the level of resistance in the plant, which continues to build resistance the longer it is on flood.

“In a field, the longer you keep that flood there and the deeper that flood is, the more tolerant or resistant that plant becomes to blast,” he says. “A little access to oxygen switches the plant back to the more susceptible stage on less resistant cultivars. So my instinct says you should be gradually increasing your flood so that by early boot, you should have a deep flood and maintain it for some time, at least through the growing season.”

Regular scouting
The final leg in disease management strategies would be scouting beginning at mid-tillering and fungicide applications when disease pressures reach economic thresholds.

Cartwright says the presence of sheath blight does not necessarily require treatment, and careful monitoring from mid-season can help growers determine if a fungicide application is necessary.

“These newer fungicides really fit into an integrated program where you can actually scout for sheath blight and make a decision to treat based on effective scouting,” he says. “You can say, ‘yes it’s there, but is it severe enough to treat?’”

Growers should begin monitoring for sheath blight at mid-season around the time of the last nitrogen fertilizer application. In Arkansas, Cartwright recommends the positive stop method, stopping 40 to 50 times within the field to determine where sheath blight is present and to what degree. Regular stops will show how prevalent the disease is and how quickly the sheath blight is moving up the plant to help determine if applications can be delayed or avoided.

“On semi-dwarf varieties, which are more susceptible, if you are finding sheath blight on every third stop, you should start thinking about treatment. On taller varieties, the threshold is about 50 percent positive stops, because they can take the pressure early without real yield loss,” he says.

Applications, if necessary, should be timed at the early-boot or mid-boot stage when they can best protect the upper three leaves of the canopy that directly affect grain and yield potential.

Monitoring for blast also begins at mid-tillering, though there is no definitive monitoring system for blast at critical stages of the disease. Leaf blast, characterized by diamond-shaped lesions on leaves, will not necessarily affect yield.

But they are 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.

With blast, Groth says, it’s important to time applications when heads are about 50 percent to 70 percent emerged from the boot, but are not yet fully exposed. Blast control requires direct fungicide contact with the head prior to infection because today’s fungicides offer little kickback or curative activity once the neck or panicle becomes infected. Lee adds that rice plants can tolerate some level of blast lesions on leaves, but panicle infections can quickly decimate yields.

Fungicide applications
Consultant Scott Taylor of Hoxie, Ark., estimates that about one-fourth of the 70,000 acres under Farm Service’s watch is typically treated with fungicides to control sheath blight or blast, while the rest is managed through cultural practices. The safety net provided by newer fungicides allows some growers to push the crop for higher yields by planting more susceptible, higher-yielding varieties and maximizing fertility, he says.

Arkansas County grower Jay Coker agrees. “These fungicides we now have available have allowed us to focus on higher inputs for the highest yield potential, because we know if we have a blowup as a result we can address it with effective fungicides,” he says.

Cartwright says the high efficacy of newer fungicides also allows growers to delay applications against sheath blight for a broader disease-control spectrum and season-long control from a single application.

“We can afford to wait a little longer because these new fungicides can stop sheath blight in its tracks and hold it for a long time,” he says.

Growers in 2002 for the first time had access to two new fungicides, Gem and Stratego, for control of blast and sheath blight. Both compounds from Bayer CropScience are based on the strobilurin chemistry trifloxystrobin.

Gem is straight trifloxystrobin, which provides some activity against sheath blight and superior control against blast. Stratego is a premix of trifloxystrobin and propiconazole, providing an economical, broad-spectrum of control that includes sheath blight, blast and kernel smut. Because of the propiconazole in Stratego, however, Stratego cannot be applied to exposed heads, so application timing becomes an issue.

Coker, who grows about 2,000 acres of rice between Stuttgart and Dewitt, in 2002 incorporated Stratego on about one-third of his treated acreage and found sheath blight results similar to his standard Quadris treatment.

Coker typically budgets for one $30-per-acre fungicide application per year, but he says variety selection and cultural practices such as sound planting, fertilizer and water management often preclude him from having to make the expense.

Still it’s good to have the tools in the shed, he says.

“You take those things, in conjunction with a fungicide program, and they keep you from having a major yield reduction or yield loss,” he says. “We might have lesions and identifiable spots with the disease, but if you did the other things right, it doesn’t have to hurt your yield.”

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

Disease control: More than just fungicides Match variety to management practices, then use inputs correctly
By Marni Katz
A collection of highly effective fungicides has given rice growers new confidence in controlling diseases, such as blast and sheath blight. But experts say an economical disease management program begins with variety and field selection and incorporates careful agronomic management in addition to well-timed fungicide applications. “An integrated approach means looking at each field, putting the right variety in with the right management practices and using inputs correctly,” says Rick Cartwright, Extension plant pathologist with the University of Arkansas Division of Agriculture. “If you do that, the whole farm enjoys maximum profit. An integrated approach is where the farmer can make more money, even if it is a little more work.” According to Don Groth, a plant pathology professor at Louisiana State University in Crowley, an integrated disease management program that will maximize yield potential and profit should incorporate the following components: • Field and variety selection, • Planting timing, • Seeding rate, • Water management, • Proper fertility, • Regular scouting and • Fungicides if necessary. Field and variety “An integrated program starts before a grower has even planted a grain of rice,” Groth says. “The first important thing is field selection, because there are certain characteristics of the field that expose it to various diseases.” A field with a history of sheath blight in rice, bad aerial blight in soybeans the previous season or where growers are following rice on rice will be at an elevated risk for sheath blight. Additionally, fields on light textured soils, where the flood cannot be well-maintained, or where trees or other factors are reducing air movement through the field will be more susceptible to blast. In those situations, Groth says it is important to plant a less-susceptible variety that will provide added protection against disease development. “Your variety selection must be matched to the field. You want to put your best sheath blight material on sheath blight ground and your best blast-resistant varieties on blast ground,” he says. Agronomic approach Growers should avoid planting extremely early or extremely late, and also manage inputs, such as nitrogen and seeding rates, to avoid lush canopy conditions that can exacerbate diseases. Groth says to plant for a targeted seeding rate of 70 to 90 pounds per acre for drill-seeded and 125 pounds per acre for water-seeded rice, depending on seed size. In addition, apply enough nitrogen, based on variety and soil type, to realize maximum yield potential while not aggravating the disease potential. Water management is the most critical component to minimizing the incidence of blast. Especially with newer, more susceptible varieties, researchers have discovered that maintaining a good flood will significantly reduce incidence of blast. “Water management is a very critical thing in trying to grow these blast susceptible varieties,” says Fleet Lee, a plant pathologist at the University of Arkansas’s Rice Research and Extension Center near Stuttgart, Ark. “If a grower is not in a position to manage his water and fertility with LaGrue, Wells and now Frances, for instance, he better be very careful with it.” Lee’s research has shown that maintaining a consistent flood 3 to 4 inches deep creates anaerobic conditions that affect the metabolism of the rice plant, making it less susceptible to rice blast. The oxygen stress actually forces the rice plant to produce ethylene, which somehow builds resistance in the plant. And Lee says the depth and duration of the flood correlates to the level of resistance in the plant, which continues to build resistance the longer it is on flood. “In a field, the longer you keep that flood there and the deeper that flood is, the more tolerant or resistant that plant becomes to blast,” he says. “A little access to oxygen switches the plant back to the more susceptible stage on less resistant cultivars. So my instinct says you should be gradually increasing your flood so that by early boot, you should have a deep flood and maintain it for some time, at least through the growing season.” Regular scouting The final leg in disease management strategies would be scouting beginning at mid-tillering and fungicide applications when disease pressures reach economic thresholds. Cartwright says the presence of sheath blight does not necessarily require treatment, and careful monitoring from mid-season can help growers determine if a fungicide application is necessary. “These newer fungicides really fit into an integrated program where you can actually scout for sheath blight and make a decision to treat based on effective scouting,” he says. “You can say, ‘yes it’s there, but is it severe enough to treat?’” Growers should begin monitoring for sheath blight at mid-season around the time of the last nitrogen fertilizer application. In Arkansas, Cartwright recommends the positive stop method, stopping 40 to 50 times within the field to determine where sheath blight is present and to what degree. Regular stops will show how prevalent the disease is and how quickly the sheath blight is moving up the plant to help determine if applications can be delayed or avoided. “On semi-dwarf varieties, which are more susceptible, if you are finding sheath blight on every third stop, you should start thinking about treatment. On taller varieties, the threshold is about 50 percent positive stops, because they can take the pressure early without real yield loss,” he says. Applications, if necessary, should be timed at the early-boot or mid-boot stage when they can best protect the upper three leaves of the canopy that directly affect grain and yield potential. Monitoring for blast also begins at mid-tillering, though there is no definitive monitoring system for blast at critical stages of the disease. Leaf blast, characterized by diamond-shaped lesions on leaves, will not necessarily affect yield. But they are 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. With blast, Groth says, it’s important to time applications when heads are about 50 percent to 70 percent emerged from the boot, but are not yet fully exposed. Blast control requires direct fungicide contact with the head prior to infection because today’s fungicides offer little kickback or curative activity once the neck or panicle becomes infected. Lee adds that rice plants can tolerate some level of blast lesions on leaves, but panicle infections can quickly decimate yields. Fungicide applications Consultant Scott Taylor of Hoxie, Ark., estimates that about one-fourth of the 70,000 acres under Farm Service’s watch is typically treated with fungicides to control sheath blight or blast, while the rest is managed through cultural practices. The safety net provided by newer fungicides allows some growers to push the crop for higher yields by planting more susceptible, higher-yielding varieties and maximizing fertility, he says. Arkansas County grower Jay Coker agrees. “These fungicides we now have available have allowed us to focus on higher inputs for the highest yield potential, because we know if we have a blowup as a result we can address it with effective fungicides,” he says. Cartwright says the high efficacy of newer fungicides also allows growers to delay applications against sheath blight for a broader disease-control spectrum and season-long control from a single application. “We can afford to wait a little longer because these new fungicides can stop sheath blight in its tracks and hold it for a long time,” he says. Growers in 2002 for the first time had access to two new fungicides, Gem and Stratego, for control of blast and sheath blight. Both compounds from Bayer CropScience are based on the strobilurin chemistry trifloxystrobin. Gem is straight trifloxystrobin, which provides some activity against sheath blight and superior control against blast. Stratego is a premix of trifloxystrobin and propiconazole, providing an economical, broad-spectrum of control that includes sheath blight, blast and kernel smut. Because of the propiconazole in Stratego, however, Stratego cannot be applied to exposed heads, so application timing becomes an issue. Coker, who grows about 2,000 acres of rice between Stuttgart and Dewitt, in 2002 incorporated Stratego on about one-third of his treated acreage and found sheath blight results similar to his standard Quadris treatment. Coker typically budgets for one $30-per-acre fungicide application per year, but he says variety selection and cultural practices such as sound planting, fertilizer and water management often preclude him from having to make the expense. Still it’s good to have the tools in the shed, he says. “You take those things, in conjunction with a fungicide program, and they keep you from having a major yield reduction or yield loss,” he says. “We might have lesions and identifiable spots with the disease, but if you did the other things right, it doesn’t have to hurt your yield.” For questions or comments about this article, contact Rice Farming editor Vicky Boyd at (209) 571-0414 or vlboyd@att.net.
Return To Top