False Smut

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

False Smut

Villosiclava virens

Fungus


In a Nutshell

  • Fungal disease that affect inflorescences and grains in later stages of rice plant development.
  • Orange and later black gall structures develop on the spikelets.
  • Grain discoloration, loss of weight and reduced germination rate.

Hosts

Rice

Symptoms

The disease affect plants during early flowering stage first and later grain formation when the spikelet nearly reaches maturity. The pathogen forms a velvety globular mass of about 1 cm in diameter on individual grains of the panicle. This structure consists of a mixture of fungal tissues and floral parts enclosed in a whitish membrane. Later on, this spherical spore bag bursts open and releases masses of orange spores. As it dries on the grains, eventually it turns yellowish green or greenish black. Most importantly, only a few grains form spore balls in a panicle and the disease is not systemic, that is other parts of the plant are not affected. The disease leads to a reduction in grain weight and seed germination.

Trigger

The symptoms are caused by the fungus Villosiclava virens, a pathogen that can infect plants at all stages but whose symptoms are only visible shortly after flowering or during the grain-filling stage. Weather conditions determine the outcome of the infection, as high relative humidity (>90%), frequent rain and temperatures ranging from 25−35º C are favorable for the fungus. Soils with high nitrogen content also favors the disease. Early-planted rice plants usually have less problems with false smut than later-planted rice. In worst case scenarios, the disease can be severe and losses can reach 25% of the crop. In India, a yield loss of up to 75% was observed.

Biological Control

The treatment of seeds at 52° C for 10 min is a effective way to reduce the incidence of the disease. Spraying the crop with copper oxychloride at the pre-flowering stage effectively controlled the disease and increases yields slightly.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatment if available. Seed treatment with fungicides do not hold the disease in check. In India, aureofungin, captan and mancozeb have been used to effectively inhibit the progression of the disease. Prophylactic spraying of propiconazole, azoxystrobin or a combination of trifloxystrobin + tebuconozole applied during the boot stage also reduces the number of false smut balls in harvested rice grain.

Preventive Measures

Use healthy seeds from certified retailers.,Use available resistant varieties.,If possible plant early to avoid the worst of the disease.,Alternate wetting and drying of the fields rather than permanent flooding (reduction of humidity).,Make a moderate use of nitrogen, and divide it in split applications.,Keep the field clean of weeds and remove infected plant debris, panicles and seeds after harvest.,Deep plow and solarization of the field after harvest also help to reduce the carry-over.,Where possible, perform conservation tillage and continuous rice cropping.