Spots of rust in the south of Mato Grosso raise alert

The MT Foundation has just confirmed, through its phytopathology laboratory, more outbreaks of Asian rust (caused by Phakopsora pachyrhizi) in commercial farming. This time in Itiquira, south of the state. The severity observed this time in areas planted at the beginning of the sowing window caught the researchers' attention.

“Another very important detail is that we found a focus of the disease in soybeans planted in the first half of October. In this region we still have soybeans sown in the second half of October and November. In other words, soybeans are one month younger than the crop where we confirmed Rust”, explains Mônica Müller, PhD and researcher in phytopathology and biologicals at Fundação MT.

The concern, according to her, is that soybeans planted later will receive much greater disease pressure. “Historically we found outbreaks in this municipality, but in later sowings, that is, in the second half of October and first half of November”, she adds.

The high occurrence of rain is the main reason that the youngest soybeans are already infected, as this scenario is extremely conducive to the disease. “We came from a previous drier period, in which the producer had better control over the health of the crop, and soon after we transitioned to a large volume of precipitation,” says the researcher.

Another problem caused by excessive rainfall is the effectiveness of fungicides for controlling Asian Rust, which with large amounts of water can be more easily "washed away" and not achieve the objective. “During the rainy season, it is even more difficult for the producer to enter the field with machinery, finding a break in the rain, with drier weather, without wind, to correctly apply the product", highlights the researcher.

important guidelines

I found Asian Rust in the field, what now? The first guideline is for the farmer not to miss any fungicide application, keep all applications scheduled, and if necessary add an application, thus providing coverage until the end of the soybean cycle.

Another important point is care with phytotoxicity. Care must be taken with the mixtures that will be made, as soy is at a more sensitive moment.

“It is worth noting that we do not recommend starting sequential applications now with a large load of product at short intervals of three, five or seven days. The fungicide will work preventively, in most cases, so the application is made to avoid new infections of the disease and very short application intervals can generate an overload of product in the plant”, points out the phytopathologist.

Harvest can make the situation worse

The rains continue in the south of Mato Grosso and Mônica remembers that the disease can complete a new cycle in seven days, and thus release new spores and, in addition, coinciding with the period when the harvest begins in the region.

“Some of the producers should intensify the harvest in the coming days, at the end of the month, and with this the disease will spread much more easily. The Rust present in these crops, with the wind, will end up moving to nearby areas, increasing inoculum in areas that were sown at the end of October and November. So now is the time to be cautious and be even more alert”, he reinforces.

The MT Foundation, through the Phytopathology and Biologicals team, made up of Mônica Müller, Karla Kudlawiec and João Paulo Ascari, closely monitors the scenario and brings updated news on MT Foundation events and social media, get in touch.

More information about Asian rust in Cultivar Grandes Culturas magazine

• Strobilurins in control (2022);

• Essential measures against Asian rust in soybeans (2020);

• Asian rust challenges in the harvest (2018);

• Resistance of Asian rust to the application of pesticides (2016);

• Chemical control of Asian rust in soybeans (2015).

History of Asian rust in Brazil

Asian rust was the subject of our cover in July 2002 (Cultivar Grandes Culturas magazine nº 41). In an article, the deceased researcher José Tadashi Yorinori (Embrapa Soja) and the researcher Wilfrido Morel Paiva (Cria/Paraguay), wrote:

"Soybean rust, caused by the fungus Phakopsora pachyrhizi, was identified for the first time on the American continent, on March 5, 2001 (W. M. Paiva), in the town of Pirapó (Itapúa), Paraguay.

It was later found, at the end of this harvest, that the disease was already widely spread in Paraguay and the State of Paraná.

In the 2001/02 harvest, the disease affected all soybean-producing regions in Paraguay. However, due to the severe drought that hit the country, there were no economic losses.

In Brazil, the disease was found in the states of Rio Grande do Sul, Paraná, São Paulo, Mato Grosso do Sul, Goiás and Mato Grosso.

The most affected municipalities were: Passo Fundo, Cruz Alta and Cruzaltinha (RS); Ortigueira, Ponta Grossa, Guarapuava (PR); Chapadão do Sul, Costa Rica, São Gabriel D'Oeste (MS); Chapadão do Céu, Rio Verde, Jatai, Mineiros, Portelândia, Santa Rita do Araguai (GO); and Alto Taquari, Alto Araguai, Alto Garças (MT).

Crop yield losses, ranging from 30% to 70%, were recorded in Chapadão do Sul, Chapadão do Céu, Costa Rica, Alto Taquari and Cruzaltinha. Only in the municipalities of Chapadão do Sul, Costa Rica (MS) and Chapadão do Céu, which represent around 220.000 ha of soybeans, losses of 30% of production are estimated (around 59.281,4 tons -- at 50 bags per hectare ) or the equivalent of US$ 13,00 million (US$ 220,50 per ton). The most affected crops lost up to 70% (harvested 840-900 kg/ha).

[...]

The expectation is that soybean rust will become a more severe and permanent disease in the high regions of the Cerrados, where there is abundant dew formation in the summer. Over the years, there will be variations in the intensity of the disease, but as a safety measure, it is advisable that the problem is taken with the utmost seriousness.

Therefore, special attention is recommended for technicians and producers in these regions. Hot periods (above 30ºC) and low humidity are unfavorable for the development of rust. However, there is little care until more knowledge is acquired about this disease."

Afterwards, evaluating the possibility of developing resistant varieties, the professor Natal Antonio Vello (Esalq) pointed out:

"The incorporation, in cultivated soybeans, of rust resistance genes, present in perennial species, has been done through artificial hybridization, embryo rescue and selection to be improved through isolation of resistance genes through the use of molecular biology, for use in the plant transformation process.

Molecular biology techniques may also contribute to the characterization of rust species and, mainly, the different races of the pathogen existing in each species. An efficient characterization of species and breeds is essential for monitoring the pathogen population and, consequently, for the good progress of breeding programs."

You can get images of the articles at the link below: