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24
Mar
2015
Reduce the risks caused by major rice diseases
Author: Yeshi Wamishe, Extension Rice Plant Pathologist

Planning ahead not only should help you manage your fields adequately but also minimize disappointment at harvest. Remember the “disease triangle” of weather, varietal susceptibility, and the presence or absence of pathogens as the three major factors that play a role for plant disease occurrence. Pathogens can be brought to a field from various sources: seeds for planting, wind from distant areas, irrigation water, insects, or farm equipment from other fields. Disease pathogen structures may also overwinter in weeds and survive in crop residues. Therefore, one can assume plant disease pathogens are present each year because they have different mechanisms to survive and spread. Varietal susceptibility to a disease varies. Some current high yielding rice varieties can be resistant to one disease but be susceptible to another. Moreover, pathogens can adapt to change resulting in new races that are capable of overcoming the plant’s natural defenses. Environmental conditions play a key role in most diseases but weather is an uncontrollable variable. Some diseases prevail every year but may not be severe all the time under natural conditions. Your management can alter natural conditions in favor of diseases. While some diseases are rare or sporadic, inadequacy in your management can cause diseases to prevail every season. Although you may not be successful to avoid all rice diseases from your field, you can substantially reduce the damage the major rice pathogens can have on your crop.

Remember: Rice blast is an unpredictable and destructive rice disease that can cause near 100 percent grain yield loss if not detected and managed in time. Blast occurred in 2013 in Arkansas mainly on late planted rice. Last year, the weather during early summer was favorable for blast disease. As a result, rice blast was reported in all major rice growing counties in Arkansas. Rice cultivars, Jupiter, CL151, Roy J, CL152, CL261, Francis, Jazzman 2, and Caffey were reported among others. Below are some tips from last year http://www.arkansas-crops.com/2014/03/05/profitable-decisions-management 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 on your farm.

Carefully select your varieties

If any of your fields have 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 compared to some 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 susceptibility of commercial varieties or the recent publications or http://www.arkansas-crops.com/2014/10/28/early-disease-management/

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 a seed treatment containing mefenoxam, fludioxonil, metalaxyl, trifloxystrobin, either individually or in combinations with 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 i.e., 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 seedling diseases go to http://www.arkansas-crops.com/2013/02/19/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 season 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 as this is 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 if 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 too susceptible to ever achieve control of the 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 for the disease problem. Consult MP154 or your county agents for more information. Remember, planning fungicide application pays off to manage unpredictable diseases such as blast in fields planted with susceptible varieties.

 


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