Pacific Pests and Pathogens Pacific Pests & Pathogens - Full Size Fact Sheets

Rice false smut (428) Print Fact Sheet

Common Name

Rice false smut. It is not a true smut, but classified in a different division of the kingdom fungi, the Ascomycota.

Scientific Name

Ustilaginoidea virens


Widespread. Asia, Africa, North, South and Central America, the Caribbean, Europe, Oceania.  It is recorded from Australia, Fiji, and Papua New Guinea.


Rice, but also recorded from maize and wild grasses.

Symptoms & Life Cycle

A fungus that colonises rice grains and converts them into a ball of fungal growth that forms spores on the outer layers (Photos 1-3). The grains become over twice their normal size. On each panicle, only a few grains are infected. At first, the spore balls are orange; later, they become greenish-black.

The life-cycle is complex and not completely understood. The spore balls contain two types of spores: i) conidia (asexual spores), which are minute and produced by the millions on the fungal balls and give them their velvety appearance; these last in the soil for about 4 months (Photo 4); and ii) sclerotia. Sclerotia are large (up to 10 mm across), dark brown, hard with irregular shape, and survive on or in the soil for up to 12 months. They eventually produce ascospores (sexual spores) from tiny toadstool-like fruiting bodies.

Which of these two types of spores is the primary source of infection is unknown. There are several suggestions: i) ascospores are released first that infect the ovaries of the spikelets as the panicles emerge at late booting stage (see Diagram for flower parts); later, conidia infect the spikelets near maturity; ii) both ascospores and conidia infect at the early stage; iii) conidia alone are the primary source at the early stage from spore balls surviving in the soil; and iv) either ascospores or conidia infect wild grasses, which produce spores that infect rice.

The disease is favoured by high temperatures (25-30°C), high humidity, and cloudy days during the time of flowering.


Mostly considered a minor disease, but there are occasional outbreaks reported from south and southeast Asian countries, with losses up to 75% from reduced grain weight as well as lower quality because of the presence of smut balls. Graham states: "A very small amount of false smut can probably be found in any rice field in Fiji, but the disease rarely causes serious losses. It appears to be more common along the south coast of Viti Levu than in the river valleys or the dry zones"1.

Detection & Inspection

Look for the orange to greenish-black balls of fungal growth on the panicles of rice plants. If unsure whether grain is contaminated, wash and collect any spores, and check identification under a microscope


Although there is speculation that the fungus is seedborne, there is no good evidence. However, visual inspection of rice seed for spores of false smut is carried out for phytosanitary certification at IRRI. Therefore, it is advisable that certified seed is always used in transfers from regions where false smut is present.


Before planting:

During growth:

After harvest:

Some varieties are said to have (low) resistance. Contact your local agriculture office for information.

The azole fungicide, propiconazole, has been found to be effective in trials, and copper fungicides have also been used to good effect. Treatments are applied during the booting stage, but the economics of fungicide use has been questioned.

When using a pesticide, always wear protective clothing and follow the instructions on the product label, such as dosage, timing of application, and pre-harvest interval.

AUTHOR Grahame Jackson
Information from CABI Ustilaginoidea virens (false smut) (2018) Crop Protection Compendium. (; and False smut. Rice Knowledge Bank. IRRI. (; and Graham KM (1971) Plant diseases of Fiji. Her Majesty's Stationery Office. London; and from Ustilaginoidea virens. Wikipedia ( Photo 1&2 William M. Brown Jr., Photo 3  O.P. Sharma, Photo 4 Cesar Calderon, Cesar Calderon Pathology Collection, USDA APHIS PPQ, Photo 5 Donald Groth, Louisiana State University AgCenter, Diagram David Condrey. grass flower with vestigial perianth or lodicules. (

Produced with support from the Australian Centre for International Agricultural Research under project HORT/2016/185: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland and the Secretariat of the Pacific Community.

This fact sheet is a part of the app Pacific Pests and Pathogens

The mobile application is available from the Google Play Store and Apple iTunes.

Pacific Pests and Pathogens Android Edition      Pacific Pests and Pathogens iOS Edition            Australian Centre for International Agricultural Research