Rice False Smut: Prevention and Control Methods and a Guide to Medication During the Growing Period

Rice false smut is a fungal disease caused by infection with the fungus Ustilaginoidea virens. False smut is also called rice kernel smut. It is commonly known as rice “wumi.” So how is rice false smut prevented and controlled? How should medication be applied during the growing period?

1. Transmission routes of rice false smut

The pathogen overwinters as sclerotia that fall into the soil, or as chlamydospores attached to the seeds. The following year, after the sclerotia germinate, they produce chlamydospores (chlamydospores: asexual spores that can be formed by all kinds of fungi, produced by fragmentation, with thick walls and a long lifespan, able to withstand adverse external environments.), and the chlamydospores in turn produce microspores and ascospores, causing primary infection.

2. How is rice false smut prevented and controlled? How should medication be applied during the growing period?

1. Select disease-resistant varieties: Different rice varieties have different resistance to false smut, so choose to plant varieties with strong resistance according to local conditions.

2. Seed disinfection: False smut can be spread through seeds, so rice seeds that have already been infected should be avoided as much as possible. When soaking seeds, use a 500-fold strong chlorine disinfectant solution for 10-12 hours of soaking disinfection, or before sowing, dress each 100 kg of seeds with 300-400 grams of 15% triadimefon wettable powder.

3. Strengthen field water and fertilizer management to promote robust growth. During the rice growing period, fertilizer should be applied rationally, with increased application of phosphorus and potassium fertilizers, to promote steady growth and enhance resistance; especially, nitrogen fertilizer should be applied with caution, avoiding excessive or too-late nitrogen application, so as to prevent excessive vegetative growth and delayed maturity, which invite disease. Promote the thin-water-and-exposure irrigation technique, pay attention to field water management in the late booting stage, avoid flood irrigation and long-term flooding, and prefer shallow-water frequent irrigation, so as to prevent excessive field humidity, which favors the germination and invasion of pathogen spores.

4. Chemical control: Time the application at the end of the booting stage.

① 2-3 days before the breaking of the boot, spray 10 g of Nativo or 10 ml of Holic EC per mu mixed with 60 jin of water. Spray once more when 1/3-1/2 of the panicles have emerged at the breaking stage.

② 5-7 days before the breaking of the boot, spray per mu 100 ml of 20% triadimefon emulsifiable concentrate or 100 g of 25% triadimefon wettable powder + 100 ml of 40% carbendazim suspension concentrate or 100 g of 50% carbendazim wettable powder mixed with 60 jin of water. Spray once more when 1/3-1/2 of the panicles have emerged at the breaking stage.

The occurrence of false smut is closely related to climate, fertilization level and varietal resistance. In rice cultivation, encountering flooding, continuous irrigation and flood irrigation is also an important factor leading to false smut epidemics. In the process of fertilization, applying too much or too late nitrogen fertilizer, as well as cultivating late-maturing varieties or transplanting too late, are all favorable factors causing the occurrence of false smut. Rice growers should apply fertilizer rationally and irrigate paddy fields rationally during the rice growing period to avoid the occurrence of false smut.

Everyone should note that the yield loss caused by false smut is not only in the grains that develop smut balls themselves, but also affects the nutrient transport to neighboring grains, thus leading to a decline in rice grain quality. Therefore, the prevention and control of rice false smut must be timely.