Arkansas Rice: Sooty Mold Not the Same as Kernel Smut

Kernel smut infected rice. Photo: University of Arkansas

When harvest is delayed due to rain or other circumstances, one of the common phenomenon in fields that received higher rates of nitrogen fertilization is invasion by sooty mold. Lodged rice can be more affected. Sooty mold is caused by several fungi that are collectively referred to as “sooty molds.”

These molds are opportunistic fungi that colonize rice panicles under wet or humid weather conditions during the maturing stages of rice. Sooty mold in rice is blackening on the surfaces of kernels (Figure 1).

The molds are superficial and basically do not affect milled rice (Figure 2). To our knowledge, sooty mold-causing fungi do not directly reduce the quality of brown or milled rice. However, the appearance of the rough rice (Figure 1) can be affected enough to be confused with kernel smut (Figure 3). Sooty molds do not cause significant problems to the rice crop but may create confusion at a mill due to hull discoloration, but the rice mills and parboils just fine (Figure 2).

To date, there is no report of sooty molds affecting yield, but the quality of bran can be low. If sooty molds appear every rice season, within-season management – primarily application of the proper levels on nitrogen and potassium fertilizers – is necessary. Generally, managing the rice crop for optimum yield and minimal disease is important to reduce sooty mold as well.

On the other hand, kernel smut (Figure 3) is one of the re-emerging diseases of rice. It is caused by a pathogenic fungus. Although infection takes place during flowering, the disease becomes evident as the crop matures.

Unlike sooty molds, the kernels are infected internally which means part or all of the kernel is replaced by black spore masses which may burst out of the hull during periods of high moisture, often in the mornings (Figure 3). The disease is favored by extended days of high temperatures and wet conditions. Both quality and yield are affected by kernel smut in fields with a disease history and excessive nitrogen fertilization.

Although both sooty mold and kernel smut spores blacken combines during rice harvest, sooty mold spores are grayish black while kernel smut spores are pure black. While both problems may discolor equipment, grain yield and quality are more affected due to kernel smut than sooty molds.

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Fig. 1. Rough rice superficially covered by sooty molds

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Fig. 2. Sooty molds on rough rice may affect bran quality but not the quality of brown or milled rice.

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Fig.3. Kernel smut pathogen infect florets internally and black spore masses replace the grain. Spores ooze out in wet conditions often in early mornings.


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