In the 2017/18 season Phakopsora pachyrhizi did not cause losses significant productivity gains in most Brazilian regions. Paraná was the state most affected by the disease. O Chemical control remains the main tool to combat the disease and the resistance of the fungus to the application of fungicides remains the greatest concern.
With soybean crops in the final harvest phase of the 2017/18 harvest, estimates released in mid- month of April show that Brazilian production of soybeans should total 114,962 million tons, an increase of 0,8% over harvest from the previous season and average productivity of 3.276 kg/ha (Conab, 2018). Good productivity reflects climate conditions which, in general, favored the culture and designed a new “super harvest” of soy in Brazil, with states such as Mato Grosso do Sul, Goiás, Tocantins, Maranhão, Piauí, Bahia, Minas Gerais and São Paulo, recording records of productivity. In this context, the occurrence of Asian rust, caused by fungus Phakopsora pachyrhizi, to be continued playing a relevant role, as its control reflects on the production cost of crops and obtaining good productivity.
The control of Asian rust is done through the adoption of various management practices, but the pathosystem surrounding the disease has been shown to be dynamic, with changes each harvest, bringing the need for constant improvement of these practices as new knowledge is acquired.
The empty health remains an important measure and, although they are often issues such as duration, effective dates and efficiency of the measure were discussed, the general consensus is that it should be maintained in states where it already exists and adopted where it does not yet exist. With this, the state of Rio Grande do Sul, as the last large producer without a sanitary void, is discussing the creation of the measure. Per In turn, the states of Santa Catarina, in 2017, and Piauí, in 2018, established sanitary void and Bahia increased its period from 60 to 99 days (Figure 1).
Another measure legislation that has been adopted more recently is the scheduling of the period soybean sowing. This measure aims to restrict sowing very late, which usually require a greater number of fungicide applications, in reason for the early occurrence of Asian rust, consequently, worsen the problem of fungus resistance to fungicides. To date, seven states adopted the calendar to limit the soybean sowing period and, in some, the limit for harvesting (Figure 2). Even so, cases of sowing late, violating state regulations, were checked.
The sowing of soybeans at the beginning of the recommended season is extremely important because it allows the “escape” in relation to the period of the most severe occurrence of Asian rust. This harvest was no different, as despite the delay in rain in some regions, most crops was sown early and, when the disease occurred, the crops were already in the grain filling phase (R5) or more advanced, in 86% of occurrences recorded on the Antirust Consortium website (Figure 3). This resulted in good control of the disease with fungicides and enabled large part of the crops did not experience loss of productivity caused by the disease.
The control chemical remains the main tool to combat Asian rust, and the fungus' resistance to fungicides remains the greater concern regarding this control method. The occurrence of resistance is a fait accompli, but the complexity of its distribution and frequency appears to have increased in the last two harvests. The use of various chemical groups and more advanced programs elaborate management methods, in addition to the high natural variability of the fungus, seem be contributing to varied situations of greater or lesser efficiency of fungicides used.
The offer of cultivars with resistance gene(s) was an advance, although still in number reduced number of materials on the market. Although they do not eliminate the need to use fungicides, the disease evolves more slowly in these cultivars, which can lead to greater security for producers, for example, in a situation where the condition climate does not allow the application of fungicide at the correct time. Is important It should be noted that the continuous use of the same cultivar can result in loss of effectiveness of the resistance gene that the cultivar possesses, so it must be Rotate cultivars with different resistance genes.
Next is presented a summary of how the 2017/18 soybean harvest progressed in the main producing states in Brazil, focusing on the occurrence of Asian rust. The information was obtained from the Antirust Consortium, the 2018 Harvest Rally, of the National Supply Company (Conab), of state agencies linked to agriculture and communications received from technicians and farmers linked to the soy production chain.
In this region, so In general, it rained regularly during the harvest, providing good plant development. Asian rust pressure and other diseases was low during much of the crop cycle, with a moderate increase in severity at the end of the cycle, in late March and early April. Therefore, record yields are forecast in these three states. On the Antirust Consortium website, the first report of Asian rust in commercial areas was on 03/01/18 in Bahia and 16/02 in Maranhão.
Nessa region, in general, the crops had good conditions for their development and showed high productivity in general. The pressure of Asian rust and other diseases was low for much of the culture cycle. As a result, record productivity is expected in these four states. On the Antirust Consortium website the first report of Asian rust in a commercial area was on 18/01 in Tocantins and 13/04 in Pará.
In Rondônia, sowing of late soybeans (safrinha) in the state is not regulated and has been carried out under the monitoring of the Agrossilvopastoril Health Defense Agency of the State of Rondônia (IDARON). Although Asian rust has been well controlled in the normal harvest, records of high severity of rust in later sowings. The first report of Asian rust in commercial area was on 28/12/17, nineteen days earlier than in the harvest previous.
At the Mato Grosso, soybean sowing occurred as planned in the mid-north and west, but with some delay in the southeast and east. Good weather conditions provided high productivity in almost the entire state, with exceptions specific cases where losses occurred due to drought in the middle of the cycle or excess of rain at harvest. Asian rust management was efficient, with first occurrence of the disease in a commercial area recorded on 22/12/17, nineteen days later than in the previous harvest.
At the Mato Grosso do Sul, weather conditions were favorable in most regions, providing high productivity for the state. Occurrences of Excessive rain during the harvest caused occasional losses. The management of Asian rust was efficient in general, but with greater severity in late crops in the south of the state. The first report in the commercial area was in the 02/01/18, 43 days later than the previous harvest.
In Goiás, although there was a delay in sowing in the southwest, most of the crops in the state developed uniformly and presented high productivity. The first report of Asian rust in a commercial area was in on 27/12/17, and although it occurred 14 days earlier than in the previous harvest, the The disease had low severity and was managed efficiently. Bigger Losses were observed in late-sown crops in the center-north. Areas of safrinha soybeans sown in an irregular period were fined by the state defense in this harvest.
In São Paulo, the crops had good conditions for their development and showed high productivity in general. However, the occurrence irregular rainfall and below normal in February, harmed some crops. The occurrence of Asian rust was low throughout most of the cycle of culture, with the first report of the disease in a commercial area on 20/11/17, nine days later than in the previous harvest.
In Minas Gerais, crop productivity was good, surpassing the harvest last year, which also had good results. Although Asian rust has been reported in commercial area on 30/11/17, 34 days earlier than harvest previous, the evolution of the disease was slow, enabling good control in most crops.
At the Paraná, despite the delay in the onset of rain in the west of the state, 66% and 98% of areas were already sown by the end of October and November, respectively. Periods periods of rain and high cloud cover, between December and January, caused physiological disorders such as pod drop, cycle lengthening and delay in harvest, in some regions, lowering the state's average productivity in relation to to the previous harvest. As a result, the occurrence of diseases was also favored in some regions, with records of occurrence of white mold and root rot of Phytophthora. In general, control of Asian rust was efficient, but with occasional losses where rain prevented entry into the field to carry out disease control at the appropriate time. There are reports of soybeans sown late with more than six applications. The Agricultural Defense Agency of Paraná (ADAPAR) authorized, exceptionally in this harvest, sowing until the day 15/01/18, due to the delay in the start of the rains. The first report of Asian rust in a commercial area was carried out on 23/11/17, seven days later than in the previous harvest.
In Santa Catarina, excess rain during some periods of the crop cycle, led to the occurrence of diseases in some areas. Occurrences were recorded of white mold, in the Planalto region, and greater severity of Asian rust in late sown areas. The first report of Asian rust in an area commercial period was on 18/12/17, 20 days earlier than in the previous harvest. In Generally speaking, the state's productivity should be good, although below that obtained in last harvest.
At the Rio Grande do Sul, the drought hit the south of the state with greater intensity, which caused a sharp drop in expected productivity. In other regions the Rains were regular, mainly favoring sowing with cultivars precocious. Later cultivars may have reduced productivity due to cause of the drought that occurred in March, mainly in the western region of state. In the mountainous region, occurrences of white mold were recorded and in the Middle Plateau, powdery mildew attacks. O The first report of Asian rust in a commercial area occurred on 16/11/17, 34 days earlier than in the previous harvest, this record being in crops sown exceptionally early for the region, in the first half of September. in a way Overall, Asian rust was well controlled, but the state's productivity will be below that obtained in the last harvest due to problems with drought, although it does not constitute a crop failure.
Asian rust did not cause losses significant productivity gains in most regions, with Paraná being the state most affected by the disease in the 2017/18 harvest.
In addition Having to rely on favorable weather, the soybean production sector has achieved good control of the disease through the joint adoption of different available management tools. However, these strategies must be used appropriately with the aim of greater efficiency and lower cost. O management of fungus resistance to fungicides is a priority topic, development of cultivars with resistance genes must be intensified, and modern technologies for monitoring diseases and applying products must be searched.
To the Legislative measures to regulate soybean cultivation have brought benefits in the control of Asian rust, but they are also capable of being modified as new knowledge is acquired, in a way that meets the needs of the productive sector, without putting the future of soybean farming at risk from the country.
Article published in issue 228 of Cultivar Grandes Culturas, May, 2018.
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Hydraulic controls are constantly evolving. However, the only guarantee of full and prolonged operation is to keep maintenance up to date and take basic care with the oils used in the system.
Choosing the soybean sowing date does not entail costs for the producer and modifies the productive potential and water availability throughout the development cycle. Furthermore, it is a strategy to minimize the risk of loss of productivity due to stress.
The disease demands correct management, with the establishment of programs that favor more than one mode of action and the use of all available chemical groups in order to avoid the selection of less sensitive or resistant fungal isolates
