Warm humid summer fostering rice diseases

By Mary Hightower

U of A System Division of Agriculture

Fast facts

Hot, humid weather aiding development of blights in rice
Timing is key to managing blast

(400 words)

STUTTGART, Ark. -- A string of hot and steamy nights has led to an increase in both bacterial panicle blight and sheath blight in Arkansas’ rice crop.

“In the last couple of weeks, we got rain without a substantial decrease in day or night temperatures,” said Yeshi Wamishe, extension rice pathologist for the University of Arkansas System Division of Agriculture. “Although it appeared good for the rice crop, the conditions seemed to favor the development of both bacterial panicle blight and sheath blight.”

SHEATH BLIGHT — Development and spread of sheath blight disease of rice under high heat and humidity. The white sclerotia formed to survive long in soil after the rice crop harvested. (U of A System Division of Agriculture photo)

She said that the bacteria that causes the panicle blight are largely seedborne, following the rice canopy upward until heading. Chemicals are not used to manage this disease.

“However, rain, particularly windy rain, plays a significant role in the spread of the bacteria and in the intensity of symptoms – assuming the infected plants are a susceptible variety,” she said.

When looking for bacterial panicle blight, growers should use caution “since there are other factors that can cause similar symptoms,” Wamishe said. “For symptom confirmation, contact your county agent.”

Sheath blight

After a very slow start in July, Wamishe said that “in a short time under the prevailing high heat and humidity, sheath blight is picking up both vertically and horizontally. Therefore, it is important to scout and take timely action.”

She said that fungicides were not recommended for sheath blight after the rice heads began filling.

“Please take the 28 days pre-harvest index into consideration before deciding on a late fungicide application for sheath blight,” Wamishe said. “Studies have shown that more than one fungicide application to manage sheath blight has not proven profitable.”

Blast

The frequent rain has also been favorable for development of rice blast – an unpredictable disease that has a talent for surviving in a variety of conditions. Wamishe said the timing and frequency of fungicide applications is important in managing this disease.

“Neck blast can cause near 100 percent grain yield loss,” she said. “Due to the airborne nature of the blast pathogen, the absence of leaf blast early in the season does not guarantee the absence of neck or panicle blast later in the season.”

Different varieties of rice have different susceptibility levels to neck and leaf blast and that puts a premium on “being ahead of the pathogen about timing of fungicide application,” Wamishe said. “Once the panicle necks are full out of the panicle booth, we cannot go back. It’s already too late.”

For more information about rice production contact your county extension office or visit www.uaex.uada.edu, aaes.uark.edu or uada.edu.

The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.

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Media Contact: Mary Hightower
Dir. of Communication Services
U of A Division of Agriculture
(501) 671-2126
mhightower@uada.edu

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