Kernel smut appears as a black mass of chlamydospores that replace all or part of individual kernels near or at maturity. Usually only a small number of kernels on each panicle are infected. Completely smutted kernels may be slightly swollen while others may break open exposing the dark spores. These black spores make the disease easy to recognize. If the disease is severe, a dark cloud of spores may be observed coming from the harvester during harvest.
Comments on the Disease
Chlamydospores liberated during harvest fall to the soil where they overwinter. The fungus can also overwinter in or on seeds. In spring as the fields are flooded, chlamydospores float, germinate, and produce other spore and mycelial stages. At flowering (heading), secondary airborne spores (sporidia) infect individual florets or kernels.
Kernel smut is generally considered a minor disease of rice. In southern U.S. rice growing areas, it is more prevalent during rainy years and in areas of fields receiving high rates of nitrogen fertilizer. Disease surveys have shown short and medium grain varieties to have lower incidence rates for kernel smut than long grain varieties. Long grain rice varieties may be more susceptible to kernel smut because their florets are open wider and longer during flowering. Because the fungus is widespread in California's rice growing areas, no effort has been made to restrict infested seed lots.
Cultural practices are the primary means of managing kernel smut. Chemicals for controlling this disease are not registered for use on rice in California at this time.
Avoid excessive rates of nitrogen fertilizer. Plant short or medium grain varieties in fields with kernel smut history. Plant certified rice seed.
Organically Acceptable Methods
All the cultural controls discussed above are organically acceptable.