Rice Farming

Although rice disease is no laughing matter, farmers can learn a lesson from stand-up comedians: Timing is everything.

“Several new fungicides are available, and timing is critical for maximum return,” says Dr. Donald Groth, professor of plant pathology at Louisiana State University’s Rice Research Station. “Each disease has its own cycle, and control practices are effective only at certain stages when the pathogen is susceptible to the chemical control and before irrevocable damage occurs.”

Johnny Saichuk, Extension rice specialist at the LSU AgCenter, agrees. “Timing is perhaps the most critical aspect of fungicide use in rice production,” he says.

First things first
Before you can determine the optimum timing, you must decide whether a fungicide treatment is needed.
“The best advice I can give farmers for determining whether a fungicide is necessary or not is to scout carefully to assess the presence and degree of disease infection,” Saichuk says.

Dr. Allen Wrather, professor at the University of Missouri’s Delta Center in Portageville, Mo., makes the same recommendation.

“The decision to use a fungicide should be based on disease severity in the field,” he says. “If a disease is severe and the variety is susceptible, then a fungicide should be applied. If the variety has some resistance, then a fungicide may or may not be needed. It will depend upon the weather forecast for the next seven to 10 days.”

An important part of scouting is determining not only the presence of disease but also the spectrum.

“The big thing is knowing which disease will be most prevalent in the field—sheath blight or blast,” Groth says. “These are the two major diseases we are trying to control, and the timing will be different for each one. Disease scouting plays a key role in determining fungicide rates, timing and need.”

Not too early ... or late
There are two obvious mistakes to avoid when it comes to timing—treating too early or too late—and either one can be costly. Louisiana, for example, has become a “one-shot market,” Groth says, so a treatment must be timed to protect the crop through harvest.

“If you apply too early, you are putting the fungicide in a bad situation for a long period of time,” he says. “You may postpone the onset of disease, but a little bit of disease early in the season is not going to do much damage.”

Waiting too long is a far more common mistake.

“Make sure the crop is protected 14 days after the head begins to move in the stalks,” Wrather says. “The biggest mistake you can make is delayed treatment.”

Yield potential can drop dramatically after a disease infection reaches a certain point.

“The period of 50 percent to 70 percent heading is a very critical stage in rice development,” Groth says.

“What we have seen is that five to 10 days after that, you start to lose a significant amount of yield potential. It is extremely important to remember that if fungicide applications are delayed after heading, significant yield and milling losses can occur that cannot be corrected by a fungicide.”

Saichuk, who helps farmers implement Groth’s recommendations in the field, echoes his advice.

“Timing is perhaps the most critical aspect of fungicide use in rice production,” he says. “I have followed Dr. Groth’s advice carefully over the years and have complete confidence in him. His research indicates many growers probably are applying fungicides too late to be of most economic benefit.”

Sheath blight and blast
Of the two major diseases, timing for sheath blight applications is much easier to determine, says Dr. Rick Cartwright, University of Arkansas Extension plant pathologist in Little Rock.

“With sheath blight, we have a fairly good understanding of scouting and thresholds where the potential economic loss would justify a fungicide application,” he says. “I recommend starting to scout within a week after mid-season fertilizer applications. If 35 percent or more of random stops have sheath blight, that field would be a strong candidate for a fungicide application. If the weather is not favorable for sheath blight, you may be able to wait a while before application.”

Keep an eye on the crop through heading, adds Dr. Gabe Sciumbato, plant pathologist at Mississippi State University in Stoneville. “A lot of our farmers who have had problems in the past just spray automatically,” he says.

Effective new fungicide options have opened the treatment window wider, says Dr. Ronnie Helms, a rice farmer, consultant and contract researcher in Stuttgart, Ark.

“Our newer fungicides are so active that they really can stop sheath blight,” he says. “What I like to do is hold off as long as possible, unless the disease is very intense and severe, and make applications from late boot through heading.”

Fungicide timing for blast can be a little trickier
“Conditions that favor sheath blight typically do not favor blast epidemics,” Cartwright says. “It’s a different type of disease. Sheath blight enjoys hot weather, but blast likes it slightly cooler with frequent light moist periods. Sheath blight is more of a problem in early planted fields, and blast is more of a problem later. We have no minimum threshold levels for deciding whether or not to spray—it is largely a judgment call.”

The University of Missouri recommends treating at about five to seven days before heading, or the late boot stage. It is especially important to treat if a susceptible variety is being grown; if the crop has excessive growth and a dense canopy; if leaf symptoms have been found in the field; if disease is present in the southern parts of fields; or if a period of cool, rainy or cloudy weather with high humidity and heavy dews is predicted during heading.

“The development of this disease is difficult to predict, and fungicide treatments are expensive,” Wrather says. “Therefore, you should treat on the basis of the above factors or automatically treat the field with a fungicide if you are unwilling to risk disease damage.”

Farmers are encouraged to closely follow state Extension recommendations and fungicide product labels to determine proper timing. Keep in mind that the first line of defense against any disease is not a fungicide, but knowledge. You should know your field history, scout carefully and understand how diseases work to be in the best position to make smart decisions.

“It all comes down to common sense,” Groth says. “We are just trying to get farmers to move a little earlier to maximize the return on their investment.”

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

New fungicides require careful attention to timing

Disease control may have been harder when there were fewer fungicide choices, but decision-making was simpler. The challenge for farmers today is to stay on top of timing recommendations for the new fungicides that have been registered in recent years.

Two effective new options are Gem and Stratego fungicides, both from Bayer CropScience. The active ingredient in Gem is trifloxystrobin, while Stratego combines trifloxystrobin and propiconazole. Gem is strong against blast, while Stratego is highly effective against sheath blight, says Dr. Ronnie Helms, a rice farmer and consultant in Stuttgart, Ark.

“Both are good fungicides with good activity,” he says.

Bayer CropScience makes these recommendations for proper timing of its two new fungicides.

• Gem: For sheath blight control, apply from panicle differentiation to boot split at the initial sign of disease. Rates and timing for sheath blight depend on crop growth stage, rice variety and disease severity.

For blast, apply Gem at mid-boot to 5 percent heading, when tips of panicles are just emerging but before full head emergence. If conditions favor blast, make a second application when panicles are 60 percent to 90 percent emerged from the boot, which will be five to 14 days later.

“Gem at heading has a little more activity against blast,” says Dr. Donald Groth, a plant pathology professor at the Louisiana Agricultural Experiment Station in Crowley.

• Stratego: For sheath blight control, begin applications before disease development, usually at or near panicle differentiation. Under severe conditions or when conditions favor disease development, make a second application just before boot split and head emergence.

“I used Stratego last year and was satisfied with it,” says Johnny Saichuk, Extension rice specialist at the Louisiana State University AgCenter in Crowley, La.

Farmers who tried Gem and Stratego last year were pleased with the results. This season should provide more opportunities to fine-tune their timing decisions for maximum effectiveness.

To scout successfully, know what to look for

Plant pathologists agree that careful scouting is the most important step in determining whether and when to apply a fungicide.

“If you are going to use a fungicide approach, I recommend understanding the disease problems on your farm and scouting,” says Dr. Rick Cartwright, Extension plant pathologist at the University of Arkansas.

“You will feel better about what’s in your field, and you also will learn an awful lot about the overall progress of your crop.”

But what exactly should scouts be looking for? Here are the symptoms for the two most prevalent diseases, sheath blight and blast.

Sheath blight is caused by a common pathogen called Rhizoctonia solani. The pathogen thrives in warm, moist weather and in thick, lush stands.

Although symptoms can appear on seedlings, they usually show up first at internode elongation. The first symptom is an oblong, water-soaked lesion on leaf sheaths at or near the water line. Within a few days, lesions will develop a grayish-white center surrounded by a dark purplish or reddish-brown margin. Tissue below the lesions, however, may remain green.

Blast is caused by the pathogen Pyricularia grisea, which overwinters in rice seeds and infected rice stubble.
Symptoms can show up on leaves, leaf collars, nodes and panicles. Look for diamond-shaped spots on leaves with gray or white centers and brown to reddish-brown margins. However, both the shape and color of lesions can vary, depending on the age of the lesion, the rice variety and environmental conditions.

While scouting for sheath blight and blast, also keep an eye open for secondary diseases that can reach economic thresholds during certain conditions. State Extension offices can provide detailed information about the symptoms that are likely to be present.

It’s about time To get the most from fungicides, scout and—if needed— apply at proper rice growth stage
By Alan Goforth
Although rice disease is no laughing matter, farmers can learn a lesson from stand-up comedians: Timing is everything. “Several new fungicides are available, and timing is critical for maximum return,” says Dr. Donald Groth, professor of plant pathology at Louisiana State University’s Rice Research Station. “Each disease has its own cycle, and control practices are effective only at certain stages when the pathogen is susceptible to the chemical control and before irrevocable damage occurs.” Johnny Saichuk, Extension rice specialist at the LSU AgCenter, agrees. “Timing is perhaps the most critical aspect of fungicide use in rice production,” he says. First things first Before you can determine the optimum timing, you must decide whether a fungicide treatment is needed. “The best advice I can give farmers for determining whether a fungicide is necessary or not is to scout carefully to assess the presence and degree of disease infection,” Saichuk says. Dr. Allen Wrather, professor at the University of Missouri’s Delta Center in Portageville, Mo., makes the same recommendation. “The decision to use a fungicide should be based on disease severity in the field,” he says. “If a disease is severe and the variety is susceptible, then a fungicide should be applied. If the variety has some resistance, then a fungicide may or may not be needed. It will depend upon the weather forecast for the next seven to 10 days.” An important part of scouting is determining not only the presence of disease but also the spectrum. “The big thing is knowing which disease will be most prevalent in the field—sheath blight or blast,” Groth says. “These are the two major diseases we are trying to control, and the timing will be different for each one. Disease scouting plays a key role in determining fungicide rates, timing and need.” Not too early ... or late There are two obvious mistakes to avoid when it comes to timing—treating too early or too late—and either one can be costly. Louisiana, for example, has become a “one-shot market,” Groth says, so a treatment must be timed to protect the crop through harvest. “If you apply too early, you are putting the fungicide in a bad situation for a long period of time,” he says. “You may postpone the onset of disease, but a little bit of disease early in the season is not going to do much damage.” Waiting too long is a far more common mistake. “Make sure the crop is protected 14 days after the head begins to move in the stalks,” Wrather says. “The biggest mistake you can make is delayed treatment.” Yield potential can drop dramatically after a disease infection reaches a certain point. “The period of 50 percent to 70 percent heading is a very critical stage in rice development,” Groth says. “What we have seen is that five to 10 days after that, you start to lose a significant amount of yield potential. It is extremely important to remember that if fungicide applications are delayed after heading, significant yield and milling losses can occur that cannot be corrected by a fungicide.” Saichuk, who helps farmers implement Groth’s recommendations in the field, echoes his advice. “Timing is perhaps the most critical aspect of fungicide use in rice production,” he says. “I have followed Dr. Groth’s advice carefully over the years and have complete confidence in him. His research indicates many growers probably are applying fungicides too late to be of most economic benefit.” Sheath blight and blast Of the two major diseases, timing for sheath blight applications is much easier to determine, says Dr. Rick Cartwright, University of Arkansas Extension plant pathologist in Little Rock. “With sheath blight, we have a fairly good understanding of scouting and thresholds where the potential economic loss would justify a fungicide application,” he says. “I recommend starting to scout within a week after mid-season fertilizer applications. If 35 percent or more of random stops have sheath blight, that field would be a strong candidate for a fungicide application. If the weather is not favorable for sheath blight, you may be able to wait a while before application.” Keep an eye on the crop through heading, adds Dr. Gabe Sciumbato, plant pathologist at Mississippi State University in Stoneville. “A lot of our farmers who have had problems in the past just spray automatically,” he says. Effective new fungicide options have opened the treatment window wider, says Dr. Ronnie Helms, a rice farmer, consultant and contract researcher in Stuttgart, Ark. “Our newer fungicides are so active that they really can stop sheath blight,” he says. “What I like to do is hold off as long as possible, unless the disease is very intense and severe, and make applications from late boot through heading.” Fungicide timing for blast can be a little trickier “Conditions that favor sheath blight typically do not favor blast epidemics,” Cartwright says. “It’s a different type of disease. Sheath blight enjoys hot weather, but blast likes it slightly cooler with frequent light moist periods. Sheath blight is more of a problem in early planted fields, and blast is more of a problem later. We have no minimum threshold levels for deciding whether or not to spray—it is largely a judgment call.” The University of Missouri recommends treating at about five to seven days before heading, or the late boot stage. It is especially important to treat if a susceptible variety is being grown; if the crop has excessive growth and a dense canopy; if leaf symptoms have been found in the field; if disease is present in the southern parts of fields; or if a period of cool, rainy or cloudy weather with high humidity and heavy dews is predicted during heading. “The development of this disease is difficult to predict, and fungicide treatments are expensive,” Wrather says. “Therefore, you should treat on the basis of the above factors or automatically treat the field with a fungicide if you are unwilling to risk disease damage.” Farmers are encouraged to closely follow state Extension recommendations and fungicide product labels to determine proper timing. Keep in mind that the first line of defense against any disease is not a fungicide, but knowledge. You should know your field history, scout carefully and understand how diseases work to be in the best position to make smart decisions. “It all comes down to common sense,” Groth says. “We are just trying to get farmers to move a little earlier to maximize the return on their investment.” For questions or comments, contact Rice Farming editor Vicky Boyd at (209) 571-0414 or vlboyd@att.net. New fungicides require careful attention to timing Disease control may have been harder when there were fewer fungicide choices, but decision-making was simpler. The challenge for farmers today is to stay on top of timing recommendations for the new fungicides that have been registered in recent years. Two effective new options are Gem and Stratego fungicides, both from Bayer CropScience. The active ingredient in Gem is trifloxystrobin, while Stratego combines trifloxystrobin and propiconazole. Gem is strong against blast, while Stratego is highly effective against sheath blight, says Dr. Ronnie Helms, a rice farmer and consultant in Stuttgart, Ark. “Both are good fungicides with good activity,” he says. Bayer CropScience makes these recommendations for proper timing of its two new fungicides. • Gem: For sheath blight control, apply from panicle differentiation to boot split at the initial sign of disease. Rates and timing for sheath blight depend on crop growth stage, rice variety and disease severity. For blast, apply Gem at mid-boot to 5 percent heading, when tips of panicles are just emerging but before full head emergence. If conditions favor blast, make a second application when panicles are 60 percent to 90 percent emerged from the boot, which will be five to 14 days later. “Gem at heading has a little more activity against blast,” says Dr. Donald Groth, a plant pathology professor at the Louisiana Agricultural Experiment Station in Crowley. • Stratego: For sheath blight control, begin applications before disease development, usually at or near panicle differentiation. Under severe conditions or when conditions favor disease development, make a second application just before boot split and head emergence. “I used Stratego last year and was satisfied with it,” says Johnny Saichuk, Extension rice specialist at the Louisiana State University AgCenter in Crowley, La. Farmers who tried Gem and Stratego last year were pleased with the results. This season should provide more opportunities to fine-tune their timing decisions for maximum effectiveness. To scout successfully, know what to look for Plant pathologists agree that careful scouting is the most important step in determining whether and when to apply a fungicide. “If you are going to use a fungicide approach, I recommend understanding the disease problems on your farm and scouting,” says Dr. Rick Cartwright, Extension plant pathologist at the University of Arkansas. “You will feel better about what’s in your field, and you also will learn an awful lot about the overall progress of your crop.” But what exactly should scouts be looking for? Here are the symptoms for the two most prevalent diseases, sheath blight and blast. Sheath blight is caused by a common pathogen called Rhizoctonia solani. The pathogen thrives in warm, moist weather and in thick, lush stands. Although symptoms can appear on seedlings, they usually show up first at internode elongation. The first symptom is an oblong, water-soaked lesion on leaf sheaths at or near the water line. Within a few days, lesions will develop a grayish-white center surrounded by a dark purplish or reddish-brown margin. Tissue below the lesions, however, may remain green. Blast is caused by the pathogen Pyricularia grisea, which overwinters in rice seeds and infected rice stubble. Symptoms can show up on leaves, leaf collars, nodes and panicles. Look for diamond-shaped spots on leaves with gray or white centers and brown to reddish-brown margins. However, both the shape and color of lesions can vary, depending on the age of the lesion, the rice variety and environmental conditions. While scouting for sheath blight and blast, also keep an eye open for secondary diseases that can reach economic thresholds during certain conditions. State Extension offices can provide detailed information about the symptoms that are likely to be present.
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