Disease Control For Missouri Rice 2014


   Disease pressure was low last year but, we better not let our guard down in 2014. Rice blast is one of the earliest known foliar diseases and it was hard to find in 2013. The blast fungus survives in various ways but often is seedborne. To reduce seedborne blast, research suggests Dynasty fungicide (azoxystrobin) at a rate above 0.75 fl oz per cwt seed as adequate. However, note that this seed treatment will not guarantee protection later in the season. We encourage field scouting, deep flood management, and foliar fungicides as needed. In blast-prone fields (lighter soils, tree-lined, low-lying, etc.), plant a hybrid or resistant variety. This takes care of the disease for the most part. Where susceptible varieties are planted in the wrong field, keep a deep flood of 4 inches on them at all times after initial flood. Fungicides work best if applied twice for blast. The first application should be made at late boot to beginning panicle tip emergence and the second when panicles are 50-75 percent out of the boot on most of the main tillers. Higher rates are best. If the field is very uniform and disease potential is low to moderate the best timing would be when panicles are emerging with about 35 percent of the length out of the boot on most of the main tillers. In uneven maturing fields, it is better to spray based on the earlier maturing parts of the field if disease pressure is substantial, and these types of fields would be almost automatic for two applications. Again, proper flood management will really help with blast management and improve performance of the fungicides.
   Sheath Blight was low in MO last year too. For many years now, strobilurin fungicides have been used to manage sheath blight disease of rice and they have been the backbone for managing fungal diseases of rice in Southern rice producing states. Current fungicides are most effective under low or moderate disease pressure. The challenge comes when varieties are highly susceptible and environmental conditions are very favorable for disease development. When we have sheath blight we recommend our producers use strobilurin+propiconazole fungicide mixtures to combat sheath blight and the smuts.
   Smuts were bad in some fields back in 2011. Fields sprayed properly with propiconazole-containing fungicides worked to minimize these diseases. In some cases, too much nitrogen was applied to affected fields and in other cases the fungicide was applied too late in the booting stage for maximum effect. The rice smuts cannot be scouted for, so preventive treatment with propiconazole containing fungicides is the only chemical control option. Fields with a strong history of the smuts, or those that have been knowingly over-fertilized with nitrogen are most at risk. Hybrid and medium grains are very unlikely to benefit from fungicide applications. Fungicides should be applied if your effective scouting indicates more than 35 percent positive stops in susceptible varieties and more than 50 percent positive stops in moderately susceptible varieties. Timing and rate of the fungicides to prevent the smuts are critical. The fungicides need to be applied at early to late boot but before heading begins on any plants in the field. Earlier is usually better in the booting stage, especially for false smut. The minimum rate of 6 fl oz tilt or tilt equivalent is now required for most effective results under current conditions, but no application will provide 100 percent control. In the past, we achieved up to 95 percent reduction in kernel smutted kernels using propiconazole with exact timing and rate but only about 65 percent for false smut (at best). Where false smut is moderate, 65 percent reduction is noticeable, but where it is heavy, control is difficult. ∆
   SAM ATWELL: Agronomy Specialist, University of Missouri
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