Starting the past couple of weeks, water is being pumped into rice fields. The rain last week has been a plus to establish permanent flood in some fields. With the preflood nitrogen applied (perhaps more than the recommended amount) and temperatures rising, rice starts to move faster and will soon reach the reproductive stage. Sheath blight is just one of the diseases of rice initiated by flooding (http://www.arkansas-crops.com/2014/05/27/pointers-blight-management/). Rice disorders known as autumn decline (Picture 1a, b & c), straighthead (Picture 2), delayed phytotoxicity syndrome (Picture 3) and dead tiller syndrome (Picture 4) could be aggravated after permanent flood is established, particularly in fields with a history of these problems.
Autumn decline (also known as Akiochi disease or ‘hydrogen sulfide toxicity’) results in black crown and root rot (Picture 1a, b & c) in rice usually beginning a few weeks after flood is established. The cause of the disease is not fully understood. The major culprit is hydrogen sulfide production in some soil types. To reduce the risk of this disease, scout your fields starting two to three weeks after permanent flooding, especially in fields with a history or suspicious fields. The problem appears worse near the wells but also can be detected in field areas far from wells. Soils with the problem may show higher pH. Affected rice fields show yellowish lower leaves and slower growth. When scouting, pull a few plants from the levee and from the bay or bar ditch to compare roots (Picture 1 C). “Drain and dry,” which allows oxygen into the soil, is the best management option available currently. To read more on autumn decline management strategy, go to http://www.arkansas-crops.com/2013/05/23/weather-and-akiochi-disease-of-rice-is-there-a-link/ and http://agfax.com/2012/06/29/arkansas-rice-root-blackening-what-we-know-what-we-dont-know/.
Straighthead (Picture 2) is a severe abnormality that may cause total grain loss unless proper management is applied. “Drain and dry” at the right timing is the recommended management option, and it is a protective strategy which means it should be done before the damage starts to show. Historically, straighthead disorder has been associated with old cotton fields where arsenic pesticides were once used. It is also associated with freshly cleared land on lighter soils with no cropping history. To read more on straighthead symptoms, management, and its similarities with glyphosate effect, go to http://arkansasrice.blogspot.com/2010/05/managing-for-straighthead-starts-early.html and http://deltafarmpress.com/glyphosate-injury-or-straighthead.
Delayed Phytotoxicity Syndrome (DPS) (Picture 3) is caused by herbicides that are applied in rice fields. These herbicides are labeled for rice. However, in some soils some microorganisms change the behavior of the herbicides and rice plants are negatively affected. “Drain and dry” has been the best management option in DPS incidence.
To read more on DPS symptoms, details on causes and management, go to lower half of the page at http://agfax.com/2014/05/28/louisiana-rice-10-things-ask-applying-fungicide/ and http://www.lsuagcenter.com/en/communications/publications/agmag/Archive/1999/winter/Delayed+phytotoxicity+syndrome+of+rice.htm
Dead Tiller Syndrome (Picture 4) caused by a Pythium species affects rice tillers. Soft rot at the base of tillers can easily be pulled out and separated. The extent of damage is limited and management options are not recommended.