Seed treatment with fungicides

In the digital era, marked by the abundant supply of information almost in real time, basic aspects to boost productivity cannot be abandoned. This is the case with the care required with the sanitary quality of seeds, whose chemical treatment with fungicides plays a fundamental role in preventing diseases in crops.

A Modern agriculture has demanded more professionalism with each harvest. The former farmer, who only performed manual labor on the farm, has given way to the new rural entrepreneur who, in addition to accompanying the countryside in his daily life, also has more up-to-date state regarding new technologies, acquisition of inputs and grain marketing.

A digital era arrived on farms with almost real-time information offering about climate, values ​​of commodities and research results that facilitate decision-making by farmers and technicians. But, on the other hand, basic aspects to achieve higher productivity has been left aside.

No It is worth choosing the cultivar most adapted to your region and with the highest ceiling productive; carry out chemical, physical and biological correction of the soil; acquire the better pesticide programs for partial area application; invest in modern machines, if the farmer forgets that the beginning of everything is in seed, which needs to be protected.

Few it is the farmers who carry out an analysis of the physiological and seed health, especially among those who “save” their own seeds. And, as there is no obligation to carry out seed pathology, Often the farmer himself is responsible for introducing new diseases or pathogen races in their areas. Approximately 90% of the crops used for human consumption come from seeds, among which Soybeans, beans, rice, corn, wheat, barley, sunflower and peanuts stand out.

At the Ministry of Agriculture, Livestock and Supply (Mapa) there are rules and Brazilian standards for sanitary analysis of seeds and such tests are main objective to determine the health condition, providing important information, such as: quarantine services, seed certification, cultural value, resistance of cultivars to pathogens, need and efficiency of treatment chemical, in addition to the quality of stored grains (EMPRAPA, 2005).

In the main cultures there are a large number of important pathogens that interfere with the germination of seeds and seedling emergence resulting in stand reduction and, consequently in the production parameters.

Among the pathogens of soybean cultivation that have been verified most frequently in the Agro Carregal Laboratory and which are disseminated by seeds stand out Phomopsis spp., Colletotrichum spp., Fusarium spp., Cercospora kikuchii, Macrophomina phaseolina, Aspergillus spp., Penicillium spp., Penicillium spp., Sclerotinia sclerotiorum e Rhizoctonia solani.

As the use of certified seeds is not a guarantee that they are free from pathogens, There is a growing need for chemical treatment.

Sclerotinia sclerotiorum

Causer of white mold in different cultures may be associated with the seed through the dormant mycelium and also by the sclerotium (resistance structure of the fungus) adhered to (GOULART, 2005). In this case, the seeds provide a safe shelter for survival of the fungus and also an efficient method of dissemination over long distances.

The incidence of this fungus in seeds can cause stand failures due to pre- and post-fall tipping. post emergency. In addition, there will be the production of sclerotia that will constitute the source of inoculum for the next cultivation. Hoffman et al. (1998) found 0,3 to 0,7% incidence of S. sclerotiorum in soybean seeds harvested in areas with a high incidence of the disease. Despite seems low, such a percentage of infected seeds can be extremely high. For a cultivar whose population is 300 thousand plants per hectare, the farmer may be introducing 900 to 2100 seeds infected by hectare, which often explains the incidence of the disease even in areas never previously cultivated with soybeans.

Due due to the difficulty of control and the potential for destruction of this pathogen, the level tolerance of Sclerotinia sclerotiorum is zero in all categories of commercialized soybean seeds. Although, this index is based only on the presence of sclerotia in the batch, and is not health testing to detect dormant mycelium is mandatory.

A best alternative for the farmer (in addition to carrying out a health analysis of seeds) is the treatment of seeds with fungicides to goal. Seed treatment can be carried out on the farm itself (onfarm) or requested when purchasing the seeds (TSI – industrial seed treatment).

Us experiments carried out during the 2017/18 harvest at Agro Carregal found efficiency of different active ingredients when compared to the control without treatment (7% incidence in artificially infested seeds). You The main fungicides were mancozeb, fluazinam, thiabendazole, carbendazim, methyl thiophanate and metalaxyl M + fludioxonil, which provided up to 100% of control.

Phomopsisspp.

the fungus Phomopsis causing dryness of the stem and pods and also of seed infection is very common in soybean growing areas, causing losses in productivity and grain quality (Wrather et al., 2010). A Premature senescence of soybean plants causes a reduction in productivity when it occurs before complete grain filling, and may also increase the infection of stems and seeds by Phomopsis spp., as senescence generally occurs under optimal environmental conditions when development of the disease (Meriles et al., 2004).

Despite the species Phomopsis longicolla be more commonly recovered from seeds than the others (Lu et al., 2010), all species of this complex can attack and affect seed quality. Infected seeds may have no symptoms, but are usually wrinkled and whitish and end up not germinating or do so more slowly, resulting in tipping over pre or post emergency. Histological studies have demonstrated that conidia of P. longicolla germinate and establish within 24 hours after arriving at the surface of the pod, noting that, after 24 hours to 48 hours, penetration into the pods occurs. The colonizations of seeds occur after colonization of the pod (DRINGRA, ACUNÃ, 1997).

Others studies have demonstrated that seeds highly infected by Phomopsis can germinate drastically reduced when evaluated by the standard paper towel roll test at 25°C. However, the emergence of seedlings from seeds in the soil test or sand is not affected if the physiological quality is good and conditions are suitable for rapid germination and emergence. These results can be explained by an escape mechanism in which the seedling, upon emerging, releases the infected seed coat in the soil, whereas in the standard germination test (roll paper) the seed coat remains in contact with the cotyledons, causing their deterioration. These results demonstrate that the standard germination test, alone, is inadequate to evaluate the quality of soybean seeds with high incidence in Phomopsis.

Superficially infected seeds per Phomopsis spp., when sown in moist soils, they usually emerge. However, the fungus developed in tegument does not allow the cotyledons to open, preventing the expansion of the primary leaves. Only infections that begin in the pods result in seed deterioration (ALMEIDA et al., 2005).

Inside disease management, treatment of seeds with fungicides from the benzimidazoles (carbendazin, methyl thiophanate and thiabendazole) can reduce transmission rate of the disease and is recommended for the control of Phomopsis spp. (Technologies, 2010).

Colletotrichum truncatum

A Anthracnose is the main disease that affects the initial phase of pod formation and one of the main problems in the cerrados. The highest occurrence can be attributed to high precipitation, high temperatures and sowing density. AND caused by the fungus Colletotrichum truncatum, with seedling death, petiole necrosis and spots on leaves, stems and pods. Inoculum from crop residues and Infected seeds can cause necrosis in the cotyledons, which tends to become extend into the hypocotyl, causing dampingoff pre- and post-emergency.

Thiram-based fungicides, benzimidazoles, certain strobilurins and some triazoles also show effective control of the disease. You More modern commercial products have shown high efficacy in controlling the pathogen in seeds.

With relation to the loss of viability of this pathogen in seeds during storage, research has shown that this fungus is more persistent than Phomopsis spp. And Fusarium semitectum, although its incidence decreases when Seeds are stored under ambient conditions for a period of six months.

Knowledge of variability space of C. truncatum, found in the fields of seed and grain production constitutes information fundamental for understanding the progress of anthracnose and for taking decision on control measures. If the primary inoculum disseminated via seed finds a favorable environment and the host is susceptible, the initial foci of infection will occur randomly in the field. Subsequently, progress of the disease in space and time will occur from the secondary inoculum source (normally originating from symptomatic cotyledons), produced in the first lesions of infected plants.

In According to Henning (2013), in Brazil no level of tolerance was established for C. truncatum in soybean seeds. Likewise, there is still not much information regarding the transmissibility from seed to plant and from plant to seed.     

Cercospora kikuchii

Cercospora leaf blight (Cescospora kikuchii) is a cosmopolitan fungus and is found in all soybean producing regions in Brazil, causing leaf blight and purple spot on soybean seeds, visually characterized by purpleing of seeds (CARREGAL et al. 2015). This fungus can reduce seed quality and germination, the incidence of which is favored by warm, humid conditions from flowering to maturity physiological status of soybeans (FAO, 1995).

To the Losses caused by this disease vary from 15% to 30% (EMBRAPA, 2000), which can result in up to 50% losses resulting from pod shock (without seeds), if a high incidence occurs in the granation stage (CHAMBER, 1998). Furthermore, early defoliation, induced by C. kikuchii, can reduce production, due to the formation of seeds of smaller size (FAO, 1995).

Infected seeds do not appear to be an important source of inoculum, except in new areas, since that the seed-plant-seed transmission rate is quite low. In the test of health, the presence of the purple color of the integument facilitates identification of the fungus, simply observing its growth and/or sporulation. The control of dissemination and transmission of pathogens by seeds can be carried out by through treatment with fungicides (MACHADO, 2000). In this case too, the more modern products that normally contain benzimidazoles in their constitution have presented efficient control.

AND It is important to highlight that seed treatment is essential to protect the seeds of pathogens already present in the soil and eradicate those that are infesting the seeds (outside the seed coat). For seed control infected, the effectiveness of treatment can vary greatly.

O farmer needs to understand that the effect of fungicides in crop treatment seeds remains effective for a period of 10 days to 15 days, protecting including the seedling (systemic products) in the first days after emergency. After this period the seedling will be unprotected and other measures Control systems such as crop rotation are essential to minimize losses. Therefore, an agronomist should always be consulted.

Geliane Cardoso Ribeiro, Luís Henrique Carregal, Agro Carregal Research and Plant Protection

Article published in issue 230 of Cultivar Grandes Culturas, July 2018.