Tuesday, May 11, 2010


It seems the flood has just been established and now it is time to drain and dry the field for straighthead control.

Straighthead is one of the oldest reported rice diseases in Arkansas, observed since the early 1900s when rice was first grown, and was especially a problem on newly cleared rice ground and lighter soil types. It has historically been associated with old cotton fields, where arsenical pesticides were once used, and arsenic has been shown to produce straighthead symptoms, however arsenic is apparently not the only cause of the problem.

Fields that favor straighthead are permanent, that is, each time rice is planted, straighthead will develop at some level if the flood is not drained and the soil aerated at the appropriate time. Historically, it is unlikely to observe straighthead on clay soils.

Straighthead symptoms include darker green plants in the paddies, followed by blanked or blanked and distorted panicles (See photo above). Medium and short grain varieties tend to have the most kernel distortion symptoms while many modern long grain varieties mostly blank out, without much noticeable distortion. Glyphosate drift during midseason can result in heavily distorted or partially blanked panicles that can be confused with straighthead. However, glyphosate injury usually affects the upper developing leaves, especially the flag leaf size, shape and texture, and can be observed in paddy rice and on levee rice. Straighthead does not noticeably affect anything except the panicle on rice and only occurs in flooded paddies. Note the photo below illustrates the deformed kernels but also a stunted flag leaf, indicative of herbicide injury.

Straighthead is a serious disease with yield losses approaching 100% if a highly susceptible variety is planted on a severe straighthead soil and not drained and dried prior to panicle initiation. Each year, we list the straighthead reactions of most varieties grown in Arkansas in the annual Rice ARPT report, available through the local County Extension office or on the Internet at http://arkansasvarietytesting.org.

If a susceptible variety is mistakenly planted on a straighthead field, the disease can be prevented by “draining and drying”. Typically, this has to be done after the field has been permanently flooded but completed before internode elongation starts. The best way to time draining and drying is by using the University of Arkansas DD50 Program, available through the County Extension Office or on the Internet at http://dd50.uaex.edu/dd50Logon.asp . This program will predict the best straighthead drain period for each field entered. If draining and drying is done improperly, you may not get the best straighthead control, or you may hurt rice yields by drying too long. 

Some growers worry that draining and drying will increase the chance of neck blast developing later. While this may be true in some circumstances, it is not a certainty, and straighthead damage is much more certain on fields with straighthead history. In order to avoid this conundrum, plant varieties that are less susceptible in known straighthead fields. If you mess up and plant a blast susceptible type, you must still drain and dry, then flood as deep as possible afterwards to minimize blast.


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