Effects of climate on FHB management in wheat

Wheat cultivation is extremely important for the sustainability of small and medium-sized properties in the southern region of Brazil. According to the National Supply Company (Conab), in the 2019 harvest in the state of Rio Grande do Sul, approximately 2.207,7 thousand tons were obtained, a number 17,9% higher than the previous season. Average productivity was 3.000kg/ha, and the planted area was 735,9 thousand hectares.

Among the factors that can affect the wheat crop cycle and affect its productivity and quality, FHB is one of the main fungal diseases that attack the crop in the southern region of the country, due to the pathogen being present in the area, as well as the occurrence of variations in environmental conditions, mainly temperature (15°C to 25ºC), relative air humidity (above 40%) and rainfall frequency, which favors the development of the disease during the winter harvest.

Evidencing alternatives for chemical control of Fusarium head blight disease, work was carried out in order to analyze the effect of different doses and times of application of the same fungicide, based on a control program in the period of heading and anthesis, depending on the index of control of Fusarium head blight disease on the yield components of the wheat crop and also verify the productivity obtained as a result of the treatments carried out.

The work was carried out in an experimental field in the municipality of Entre-Ijuís (Northwest of Rio Grande do Sul) in the 2019/2019 winter harvest, with the cultivar “TBIO Sossego”, on June 12th.

The work included 40 plots divided between ten treatments, with treatment 1 being the control without any fungicide application and the other treatments with applications of the same fungicide (metconazole + pyraclostrobin) at a dosage of 0,75L/ha, with an increase in dose. in treatment 10 to 1L/ha. The application times were: treatment 2 (application at 5% of spike), treatment 3 (applications at 5% of spike; 5% of anthesis and 5% of anthesis + 15 days), treatment 4 (applications at 5% of spike and 5% anthesis), treatment 5 (applications at 5% anthesis and 5% anthesis + 15 days), treatment 6 (applications at 5% anthesis and 5% anthesis + seven days), treatment 7 (applications at 5% spike + seven days and 5% anthesis), treatment 8 (applications at 5% spike + seven days; 5% anthesis and 5% anthesis + seven days), treatment 9 (applications at 5% anthesis ; 5% anthesis + seven days and 5% anthesis + 15 days) and treatment 10 (applications at 5% spike; 5% anthesis and 5% anthesis + 15 days). Fusarium head blight incidence and harvest analyzes were carried out at the Phytopathology Laboratory at URI Santo Ângelo, in Rio Grande do Sul.

The above-normal rainfall, which occurred in the 2019 harvest, may have been the determining factor for the high intensity of the disease in the experiment. This fact was associated with the anthesis stage, which allowed a sufficient incidence to discriminate between treatments in terms of control effectiveness and productivity.

Fusarium head blight in wheat was first detected in treatment 1 (control plot without any fungicide application), which showed approximately 80% incidence of the disease in the crop, being statistically higher than the other treatments (Graph 1). This percentage of FHB shows that the treatments were exposed to a significant amount of the disease in the field, due to the environmental conditions during the pre-anthesis, anthesis and post-anthesis period, and were favorable to the development of the disease in the crop.

The high incidence of the disease may also be correlated with the previous winter crop (ryegrass). As it is a saprophytic fungus, it survives in cultural remains from different cultures (Reis et al., 1995). However, Almeida (2006), studying forms of management in direct planting, observed that in years of Fusarium head blight epidemics, the preponderant factor for the occurrence of a higher incidence of the disease was the climatic condition at the time the plants were harvested and not the quantity or origin of straw. of the predecessor culture.

Fusarium head blight infects ears in conditions of high humidity favored by long periods of wetness, that is, greater than 30 hours (Del Ponte, 2007). As well as temperatures between 20°C and 30ºC combined with this factor favor the infection of the fungus (Del Ponte et al., 2004), and this is in line with the rainfall and temperature in the period related to earing and anthesis in the location of the experiment carried out in this research.

In studies by De Luna et al. (2002), the authors concluded that the increase in spore release occurs during and up to six days after rain, although they are released in its absence. Rain would trigger the final maturity of ascospores and perithecia before release. According to studies by Paulitz (1996), light rain temporarily removed spores from the air, while continuous rain of great intensity promoted the same effect for a longer period. Therefore, the rainy period during anthesis is considered a highly contributing factor to pathogen infection.

During this study, the occurrence of precipitation three days before and after the treatment application periods indicates a favorable wetting condition for the pathogen (Figure 1). In addition to the wet condition, the temperature favored the disease.

In the months of September and October, average temperatures were 16,4°C and 20,8°C, remaining in ranges suitable for development and, therefore, the occurrence of FHB epidemics in the crop, causing instability in the crop. wheat. In September, the total volume of precipitation was 82,6mm. In October, the volume was higher, reaching a total of 305,8mm. In general, periods of three continuous days of rain and average temperatures above 17ºC predispose to infection. These factors were predominant for the incidence of the disease in the area evaluated.

Among the other treatments, it was observed that T2 (5% anthesis) and T5 (5% anthesis; 5% anthesis + 15 days) were statistically similar, showing themselves to be the worst treatments for fungicide application times of the year. experiment. Although in both treatments the applications were carried out at 5% anthesis, in T2 the next application did not occur and in the case of T5 it did, but it was late, not sufficient to control the disease. According to Reis et al. (1996), the best control is observed when fungicide is applied at the time when the wheat has a greater proportion of ears with exposed anthers, that is, approximately eight days after the beginning of heading.

Reis (1988) analyzed the non-uniformity of wheat anthesis, in which he observed that its duration can be four days in an ear, 12 days in a plant and up to 25 days in a crop. The non-uniformity of flowering may be one of the reasons for the low level of control obtained regarding the times of application of fungicides in the field. Greater efficiency can perhaps be obtained using cultivars with uniform flowering.

When comparing the results obtained in treatments T4 (5% spike; 5% anthesis) and T10 (5% spike; 5% anthesis; 5% anthesis + 15 days), it is observed that they also presented percentages statically similar. In both treatments, applications occurred at 5% of anthesis, but in T4 there was an application prior to anthesis, at seeding. In T10, this application did not occur, but rather a subsequent application, 15 days after 5% of anthesis. The dose factor at T10 did not contribute to the increase in efficacy.

When analyzing the climatic conditions during the period of application of treatments T4 and T10, it was found that they were favorable to infection, and may have caused an increase in the density of inoculum in the air, mainly due to the frequency of rain that occurred in the four days prior to the application of the treatment. . Due to this, the incidence of the disease obtained the best conditions for progression. Therefore, both treatments proved to be statistically inefficient in controlling the disease. The application prior to anthesis (spiking) was not responsive under the climatic conditions presented. In the same way that Milus & Parsons (1994) found in their studies that fungicides, when applied before anthesis, have no effect on the disease.

The variables of treatments T3 (5% spike; 5% anthesis; 5% anthesis + 15 days) and T7 (5% spike + seven days; 5% anthesis) presented statistically similar percentage values ​​of FHB. Applications were carried out in both treatments in the period before anthesis, however, in T3 the application was carried out at 5% of the spike and in T7 the application was carried out after seven days of 5% of the spike. Like the periods of anthesis, they coincided with periods of wetness and high temperature conditions. It is understood that these allied factors may have favored the infection of the pathogen, resulting in the high incidence and severity of the disease. This suggests the reason for the low efficiency of both treatments in controlling the disease.

When comparing treatments T3 (5% spike; 5% anthesis; 5% anthesis + 15 days) and T10 (5% spike; 5% anthesis; 5% anthesis + 15 days), the application times were the same, but in T10 the dose of fungicide used was 1L/ha, while in T3 a dose of 0,75L/ha of the same product was used. However, the results show that the treatment with a lower dose had a significantly lower percentage of FHB compared to the treatment with a higher dose. Therefore, it is understood that there is no need to increase the dose of the fungicide under this same control position.

In treatments T6 (5% anthesis; 5% anthesis + seven days) and T8 (5% heading + seven days; 5% anthesis; 5% anthesis + seven days) the percentage values ​​of FHB were presented statistically similar. In both, the application was carried out at 5% of anthesis and another after seven days, showing that the application that was carried out in T8 prior to 5% of anthesis, was not statistically different from the other treatment, and in this case, this application was unnecessary. prior to controlling the disease. Reis (1988) reports that two applications during anthesis could have a better effect. Therefore, in the results of this application it was found that two applications during anthesis proved to be the second best treatment in the experiment.

Treatment 10 (5% heading; 5% anthesis; 5% anthesis + 15 days) showed that even with an increase in the fungicide dose (1L/ha), it was not possible to compensate for the positioning failure. Therefore, the timing of application is even more important than increasing the dose.

Thus, when observing the meteorological conditions, it appears that on 17/9/2019 and 2/10/2019 the rainfall coincided with the applications of the treatments, but the applications occurred before the rain, which indicates that the protection of the fungicide prior to the wetting period proved to be convenient in treatments T6, T8 and T9 (5% anthesis; 5% anthesis + seven days; 5% anthesis + 15 days).

The lowest incidences of FHB were detected in spikelets from treatment 9 (5% anthesis; 5% anthesis + seven days; 5% anthesis + 15 days), with almost 10%, resulting in the highest efficacy found. This was, statistically, the best treatment in the study, also reflecting greater productivity (Graph 2).

Making a parallel between application, plant stage and climate, it was possible to observe that the beginning of anthesis occurred in a dry environment (1st application). Soon after the 2nd application, there were eight days with rain and cloudy days and then dry weather again, in the 3rd application.

In short, the analysis shows that the 2nd application, before the start of rain in the anthers, was a determining factor in preventing the increase in the incidence of FHB. This was the only difference for the T5 treatment, but with almost 30% less control. Possibly, in this treatment 9, the protection of the spikelets was maximum, showing that the ideal period of application should be extended, as the anthers are emitted, especially if there is precipitation at this stage.

Jaíne Iung da Silva, Eduarda Casarin Kronhardt, Eduardo Argenta Steinhaus, Luiz E. Braga and Marcelo Gripa Madalosso, Universidade Regional Integrada, Campus Santo Ângelo – Plant Protection Group

Cultivating Great Crops September 2020

With each new edition, Cultivar Grandes Culturas publishes a series of technical content produced by renowned researchers from all over Brazil, which address the main difficulties and challenges encountered in the field by rural producers. Through research focused on controlling the main pests and diseases in the cultivation of large crops, the Magazine helps farmers in the search for management solutions that increase their profitability. 

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