Integrated management of rice blast in irrigated rice

Preventive chemical control and cultural and genetic control measures are essential to combat the disease

10.02.2020 | 20:59 (UTC -3)

Blast is the main disease in irrigated rice in Rio Grande do Sul. With a high potential for damage, it can compromise productivity by 100% when conditions favorable to the pathogen are present. The use of preventive chemical control, with reduced intervals between applications, is an important tool for integrated management, which should not dispense with cultural and genetic control measures.

Blast damage to rice productivity and quality varies depending on a series of factors, such as the cultural practices adopted, the degree of susceptibility of the genotype, climatic conditions, the level of pathogen inoculum, the moment at which the disease settles in the crop, among others. Blast symptoms on leaves begin with small necrotic spots that increase in size, acquiring an elliptical shape, with brown edges and a gray or whitish center. Blast is common in the leaf collar region, which can cause leaves to fall and die (Figure 1). By infecting rice leaves, rice blast causes indirect damage to production, reducing the active leaf area and, consequently, the productive potential of the crop.

Blast can also affect rice panicles, colonizing the first node below the panicle (Figure 2). This incidence is called panicle base blast, also known as “neck blast”, where the disease directly affects rice productivity, preventing the accumulation of carbohydrates in the grains, reducing grain weight and the percentage of grains formed.

The high productive potential that current rice hybrids and cultivars present is linked, in most cases, to a low rusticity of the genotypes. Thus, as a result, there are materials that are very susceptible to the occurrence of diseases and highly sensitive to stress factors, both biotic and abiotic. The adoption of integrated management practices, such as the use of resistant cultivars, sowing within the preferred season, balanced fertilization, adequate irrigation and the use of chemical control through the application of fungicides, is fundamental for the efficient management of blast in the crop. irrigated rice.

The use of fungicides to manage blast must be used as a tool within Integrated Disease Management and not just as an isolated control method. The use of chemical disease control in irrigated rice cultivation aims to maintain the productive potential and quality of production, protecting the crop from the harmful effects of diseases.

    Choosing the ideal time and number of fungicide applications in irrigated rice is a difficult decision that depends on a series of factors. It is possible to mention the level of susceptibility of the cultivar, the management used to conduct the crop, the presence of pathogen inoculum and outbreaks of the disease in the crop, the history of blast occurrence in the area, the phenological stage of the crop, the presence of climatic conditions favorable to blast, among others.

    In the 2013/14 harvest, in the municipality of São Sepé, Rio Grande do Sul, an experiment was conducted with the objective of evaluating the performance of seven chemical blast management programs. The programs were composed of a Control treatment (without fungicide application) and six treatments with chemical control, which differed only in terms of the number and timing of fungicide applications (Table 1).

The effect of the treatments was evaluated on the control of leaf blast, the incidence of blast at the base of the panicle and the productivity of irrigated rice (Figures 3 and 4). The intensity and severity of blast occurrence in rice crops, during the experiment, were extremely high (Figure 3). The first symptoms of the disease were observed when the rice was still in the vegetative phase, before the cotton stage, and the disease showed a significant increase until the physiological maturation of the crop. It can be observed that none of the treatments tested promoted total control of the disease, that is, even with the application of chemical management programs, there was an occurrence of blast on the leaves and incidence in the rice panicles. This is a situation that proves the importance of carrying out Integrated Disease Management, with the integration between cultural, genetic and chemical control methods, as when using only the application of fungicides as an isolated tool there will be difficulties in efficiently controlling blast. .

Due to the high blast attack, the damage to the control's productivity was 73,4%, when compared to the treatment where three applications were carried out (Figure 4). This result indicates the enormous damage potential of rice blast in rice crops and the importance of carrying out adequate management of the disease in order to avoid the occurrence of high damage.

The use of preventive chemical control, with reduced intervals between applications, is an important tool for blast management. However, integration between cultural, genetic and chemical control methods is essential for the efficient management of rice blast in irrigated rice cultivation.

Table 1 – Phenological stages at the time of applications to control Pyricularia oryzae. São Sepé (RS), 2014
Table 1 – Phenological stages at the time of applications to control Pyricularia oryzae. São Sepé (RS), 2014

Figure 1 – Symptoms of rice blast on the leaves and collar of the flag leaf Photo: Felipe Frigo Pinto
Figure 1 – Symptoms of rice blast on the leaves and collar of the flag leaf Photo: Felipe Frigo Pinto

Figure 2 – Symptoms of rice blast at the base of the rice panicle (“neck” blast) Photo: Felipe Frigo Pinto
Figure 2 – Symptoms of rice blast at the base of the rice panicle (“neck” blast) Photo: Felipe Frigo Pinto

Figure 3 – Area under the blast progress curve and incidence of blast at the base of the panicle in irrigated rice under different chemical management programs. São Sepé (RS), 2014 *Averages followed by different letters, lowercase for AACPB and uppercase for Incidence, differ from each other, at a 5% probability level, using the Skott Knott test. CV % for AACPB = 57,89; CV % for Incidence = 11,75.
Figure 3 – Area under the blast progress curve and incidence of blast at the base of the panicle in irrigated rice under different chemical management programs. São Sepé (RS), 2014 *Averages followed by different letters, lowercase for AACPB and uppercase for Incidence, differ from each other, at a 5% probability level, using the Skott Knott test. CV % for AACPB = 57,89; CV % for Incidence = 11,75.

Figure 4 – Irrigated rice productivity under different chemical management programs. São Sepé (RS), 2014 *Averages followed by different letters differ from each other, at a 5% probability level, using the Skott Knott test. CV % = 22,47.
Figure 4 – Irrigated rice productivity under different chemical management programs. São Sepé (RS), 2014 *Averages followed by different letters differ from each other, at a 5% probability level, using the Skott Knott test. CV % = 22,47.


Felipe Frigo Pinto, Ricardo Silveiro Balardin, Marcos BelinazzoTomazetti, Jacson Zuhl, Bruno Pedro Lazzaretti, Federal University of Santa Maria (UFSM), Collaborators from the Phytus Institute (IP)


Article published in issue 193 of Cultivar Grandes Culturas. 

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