Arkansas Rice: “Underwater” Diseases
Rice fields in some counties are “underwater “due to the excessive rain in the last days of June. As I drove (07/02/14) in Monroe, Woodruff, and St. Francis Counties, I saw fields of soybean and rice covered with water. Information on soybean conditions has been given here. Though not as fast as soybeans, rice in an “underwater “situation could also die unless it possesses specialized genes that enable it to breathe.
The rice cultivars we grow here currently do not have those genes to my knowledge. However, as rice is more resilient under excessive water, I would like to speculate the possible disease related problems that may be associated.
Although rice leaf blast has been on the go in the last two weeks, the fungus that causes rice blast does not like anaerobic conditions. Therefore, the disease would be suppressed and momentarily, it will not be a problem in these fields.
Autumn decline that makes roots black and causes root rotting is a phenomenon that worsens in anaerobic conditions. Therefore, the excessive water could aggravate the problem more in fields with history.
The fungus that cause sheath blight in rice is ubiquitous and may take chance to reach to the upper canopy faster than normal since the fungus structures that start infection normally float on flood water. Infection could start at any water level in the height of the crop. Therefore, it is likely to detect sheath blight lesions at the upper leaves and sheath after the flood subsides. Note that the upper three leaves including the flag leaf are very important for yield and quality of rice grain and they should be protected.
Other than these, stress symptoms and minor root, sheath and leaf diseases may also be associated in incidental underwater situations. Too much of a good thing may not be necessarily good.
What we need to do:
If possible, lower the water level to salvage the crop as soon as possible.
Scout for autumn decline (black root rot). Rice roots from the deep water part of the field (which is anaerobic) need to be compared with rice roots from the levee. In the presence of autumn decline, the field needs to be “drained and dried” to allow oxygen in to soil. To read more on scouting and management of autumn decline, go here.
Scout for sheath blight–taking the level of excessive water into consideration, scout both lower and upper rice crop canopy for possible sheath blight lesions. To read more on scouting and management of sheath blight go here.