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26
Mar
2012
Plan Now to Minimize Rice Disease Problems
Author: Yeshi Wamishe, Extension Rice Plant Pathologist

We do not know the effect of the mild winter on diseases we may battle this growing season, nor can we control the weather this summer, but we can think ahead to help minimize certain risks.

Disease management starts with picking the right variety for the field.  If you plant the correct variety in each field, based on known field problems, then manage them effectively, the entire farm will reach its maximum productivity at minimum risk.  Of course, this means planting more than one or two varieties on many farms.

Hybrids have the best disease resistance of current rice varieties, so fields with a history of disease problems would be good candidates for hybrid rice.  On the other hand, fertile, wide-open fields planted early, with excellent water and timely management during the season might benefit when planted with a Clearfield or conventional pure-line variety like CL151, CL111, CL152, CL142AR, Taggart or Roy J, among others.  For later planting, where blast and smut diseases may be favored, then hybrids would again be the best choice with respect to disease management.  In addition, planting high-quality seeds treated with an appropriate fungicide and insecticide minimize seed rotting, encourage emergence, and produce vigorous seedlings that can withstand early season weather misfortunes.

Soil fertility plays a major role in disease severity.  If too much nitrogen is applied pre-flood, that field could develop more severe disease. Too much early nitrogen strongly encourages sheath blight, blast, kernel smut and false smut among other diseases.  For fields with a history of heavy disease, it is likely that too much nitrogen is in play, so working with the county agent or consultant to determine how much to “cut back” is advised.  In this regard, the new nitrogen soil test for rice (N- ST*R), could help to determine the available nitrogen in the soil and provide a more exact recommendation for N. Please contact your county agent for information on N- ST*R.

In addition, higher levels of soil potassium reduce the severity of many diseases including stem rot, brown spot and likely sheath blight and bacterial panicle blight, among others.  In general, rice that is managed with regard to balanced fertility tolerates disease and other stress better.

Planting early provides adequate time for rice plants to develop maximum yield potential and better escape many late season diseases including blast, narrow brown leaf spot and the smuts.  In addition, effective water management minimizes plant stress, and thus stress-related diseases like blast and probably bacterial panicle blight.   Before planting is the time to decide how much land can be effectively irrigated without stress to rice or nearby rotation crops.  A common mistake is to plant too much rice in fields with inadequate water capacity during the hot dry summer months, when all crops need irrigation.

Timing and rate of fungicide application are key elements for effective disease management.  Preventative applications for the smuts need to be made between 2-inch panicle elongation and before fully swollen boot to give the fungicide time to get into the plant tissue.  Based on recent observations, the 6 fl oz per acre rate of propiconazole, formulated as Tilt fungicide or equivalent, seems to be required.  Lower rates no longer appear to be working under our conditions.

Research has shown that many fields do not benefit from preventative fungicide applications, and spraying every field without scouting year in and year out will result in the development of resistant strains of the sheath blight fungus and the blast fungus, among others.  Therefore, scouting effectively and using our fungicides wisely can preserve them, and new fungicides for rice will be rare in the near future.

Fungicides are most effective on well-managed rice, and may fail where too much nitrogen, too little potassium or poor irrigation management make the rice crop simply too susceptible to control disease.  As in football, there is no substitute for being good at the fundamentals and for thinking ahead, and this is true for profitable rice disease management.

Please contact your local county extension agent for additional information.


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