Plan Ahead To Make Profitable Decisions About Rice Disease Management


   I hear some saying that the crop season in 2014 will be a “normal” one following such a severe winter. Although I did not like the winter, my wish is that the cold temperature has effectively suppressed rice pathogens. However, since we cannot be sure of this and the source of inoculum for all diseases is not soil, we need to plan ahead to minimize disease risk. Below are some tips to help you make profitable decisions concerning rice disease management.
   Know the history of each field
   Disease management starts by planting the correct variety to your individual fields.  In doing so, each of your fields will reach their maximum productivity with minimal risk. However, this means planting more than one or two varieties across fields.
   Carefully select your varieties
   If any of your fields have a history of diseases such as blast, kernel smut, false smut, or bacterial panicle blight, and you run late in planting, hybrids would be better candidates. Hybrids have the best disease resistance of current rice varieties. However, fertile, wide-open fields with very good water supply will benefit if planted early with Clearfield or conventional pure-line varieties such as CL151, CL111, CL152, Taggart, or Roy J, among others. Refer to MP 192, Table 11-1 Arkansas Rice Production Handbook page 126 for disease reactions of commercial varieties.
   Understand that soil types of your fields can impact variety emergence and performance
   There are variations in seedling emergence among varieties in different soils. If you know your fields and varieties, matching them accordingly would be beneficial. To reduce seed rotting by soil fungi, planting high-quality seeds treated with appropriate fungicides and insecticide is recommended. Seed treatments encourage emergence and help with seedling vigor. Vigorously growing seedlings can better withstand early spring adverse conditions.  Gibberellic acid seed treatments may also be beneficial in fields with a history of poor emergence, particularly if you are planting a variety with moderate to weak seedling vigor. Before planting, make sure the seeds are all uniformly covered with the seed treatments. As seedling diseases are complex, use the higher rate of seed treatment containing mefenoxam, fludioxonil, metalaxyl, trifloxystrobin, either individually or in combinations of two fungicides, for early planting or severe disease situations. The extent of seedling vigor and early season stand can be good predictors of the prospect of the field in the season.  The blast fungus survives in various ways but can also be seedborne. To reduce seedborne blast, research suggests application of the fungicide azoxystrobin (e.g. Dynasty) to the seed at a rate above 0.75 fl oz per cwt.  However, note that this seed treatment will not guarantee protection later in the season for later stage blast such as neck blast. Therefore, we encourage regular field scouting, proper flood management, and foliar fungicides as needed. (See MP154 for fungicides and MP144 for insecticides.) To read more on rice seedlings go to 2013 Plan ahead to minimize rice seedling diseases.
   Plant at suitable time
   If weather permits, plant early.  Early planting provides adequate length of time for maximum potential of vegetative and reproductive growth resulting in better yield and quality. A better crop stand usually equates to better disease tolerance. Moreover, early planting gives your crop a better chance of escaping diseases such as blast, bacterial panicle blight, and false smut that are normally encouraged by late weather conditions.
   Balance nutrients/ soil fertility
   Research has shown that diseases can be managed with balanced nutrition. In situations where excessive pre-flood nitrogen is applied, diseases such as sheath blight, blast, kernel smut, and false smut, among others, have been seen to severely damage yield and quality. Recent findings have indicated that bacterial panicle blight increases with excessive nitrogen. Soil testing for nitrogen level and appropriate application of fertilizers is highly recommended. Adequate soil potassium has been determined to reduce stem rot, brown spot, sheath blight, and possibly bacterial panicle blight. We need to pay special attention to fields with a history of one or more of these diseases.
   Manage your field with sufficient water
   Before planting decide how much land can be effectively irrigated without stressing your rice crop.  If you do not have adequate water to flood your rice, you should consider a rotational crop for some of your fields.  Adequate water is vital for rice development from germination until physiological maturity.  The reproductive stage of rice is greatly affected by a shortage of water. The “drain and dry “strategy for autumn decline or straighthead management requires caution because the stress placed on plants as a result of this management strategy can be exacerbated by insufficient water. A common mistake is to plant too much rice in fields with inadequate water capacity during the hot dry summer months – when the crop needs more irrigation.
   Know the appropriate fungicides for common diseases and check ahead for availability
   The primary disease management options are using resistant varieties and cultural methods. The use of fungicides should be the final option. Prophylactic (protective) application for sheath blight is not recommended. Scout and apply fungicides only when needed. Protective fungicides are applied based on the history of the field, the variety, and your management with soil fertility. Fungicides are most effective on well-managed rice and may fail where too much nitrogen, too little potassium, or poor irrigation management practices have been utilized. These conditions can make the rice crop simply too susceptible to control disease.
   Time your fungicide application with the right rate and product
   Fungicides need to be applied at the right rate and time to provide the most benefit in your well managed fields. In order to get the desired level of disease suppression, foliar fungicides need to be mixed with adequate amounts of water to provide good coverage. Lower rates either are ineffective or would suppress the disease for a shorter duration compared to the recommended rate. Make sure you are using the correct product. Consult the MP154 or your county agents for more information.∆
   DR. YESHI WAMISHE: Extension Rice Plant Pathologist, University of Arkansas
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