Measures to control Asian rust in soybeans

From the hard lessons left by Asian rust over 15 years in Brazil, respect for the sanitary void and the elimination of tiguera plants that remain in crops, as well as those that grow in urban areas and on the sides of highways, are indispensable measures to allow living with this aggressive disease and increasing the useful life of available control technologies.

The economic importance of soybean farming for the country is indisputable, an oilseed that simply transformed Brazilian agricultural production, brought employment and income to millions of people, in addition to feeding billions more around the world. The introduction of Asian rust in Brazil caused great concern right from the beginning, which resulted in serious losses for soybean farmers in general. In Mato Grosso, the largest national producer, the situation became more visible, an almost state of calamity was installed in the first years of its detection. The ideal climate conditions, favored by the extensive areas irrigated during the off-season, worsened what was already critical, especially in the southeast region of the state, in the municipality of Primavera do Leste, a city that became known as the rust capital of the world.

In the 2002/2003 harvest, the disease began to cause serious damage in Mato Grosso, but it was in the following harvests, especially in 2004/2005, that the extent of the crisis was realized. The disease began to be detected even earlier, in the vegetative phase. The rust was out of control. Producers selling their land, thousands of unemployed people wandering aimlessly through the cities, an increase in urban violence, true social chaos was what was happening. Soybeans grown under central pivots were the great multipliers of spores during the off-season and from there expanded into summer crops. Newly sown areas alongside older crops would soon be infected by rust, so the situation became chaotic.

At the beginning of 2005, there was a visit from the late José Tadashi Yorinori, a man with in-depth knowledge of the disease and who gave guidance, showed where the problem was and taught how to deal with the situation. On a napkin, after meeting with producers and irrigators in the region, in a restaurant in Primavera do Leste, he outlined the idea of ​​the soybean health void. I was a witness to this. At that moment it was no longer possible to edit regulations, producers had already planned for planting. On March 18, 2005, at the 17th meeting of the Plant Health Defense Commission - CDSV/MT, it was suggested the publication of a Recommendation for producers not to cultivate soybeans under a central pivot in that 2005 off-season. in Mato Grosso (SFA/MT) and the Agricultural Defense Institute (INDEA/MT), after hearing the Mato Grosso Plant Health Defense Commission (CDSV/MT), with the participation of the Association of Soy Producers of the State of Mato Grosso (APROSOJA), published, on the same date, March 18, 2005, Joint Technical Recommendation No. 01/05, proposing a soybean off-season calendar for the entire State of Mato Grosso. In that first year there was already a lot of criticism, among them that with the restriction of soybean planting under central pivots, seed producers from Serra da Petrovina would be privileged... As it did not have the force of law, the recommendation had no effect even though it had the support from Aprosoja. On 02/06/2055, CDSV/MT met in Primavera do Leste to discuss the issue of Asian rust and central pivots, “to precisely provide irrigators and agronomists in the region with the opportunity to expand discussions on the topic”, according to appears in the minutes. Still in the same year, on 30/11/2005, the CDSV-MT unanimously approved the creation of the soybean sanitary void for a period of 90 days, so that on 16/12/2005, Normative Instruction No. 04/ 2005. There, the Soy Sanitary Vacuum was established, the first in the country, which came into force in the 2006 off-season.

The gains in productivity and the reduction in costs were immediately noticeable, rust began to arrive later in the crops, and savings were made on applications. This convinced soybean farmers and the practice proved to be efficient. Since then, there have been constant advances, improvements, acceptance and commitment from the overwhelming majority of producers in the full implementation of the sanitary void. Currently, a planting calendar has also been established, from 16/09 to 31/12 and all soybeans must be harvested by May 05th of each year.

However, there are still some points that can be improved. Raccoons continue to be the big villains. Some producers are still notified every year and, after the inspection visit, they end up fulfilling their role. But others still believe that, even with rust, the guax plants on their property will die due to the drought and that chemical or mechanical control would be unnecessary. Maybe they think that a dry, dead soybean plant no longer transmits the disease. It is true that rust, an obligatory pathogen, needs living tissue to continue multiplying, but the spore produced when the plant was still green survives, even with dry leaves. Experiments conducted in the laboratories of the Federal University of Mato Grosso showed that the rust remained viable and infective for up to 42 days after the leaves were harvested and kept dry in paper bags. This shows the importance of the raccoons being destroyed before the sanitary vacuum begins. It is still possible to move forward in this direction, you cannot take any risks, especially if there is a period of rain in the middle of the year.

Another critical point that has favored the survival of rust are the plants that grow in cities and along highways, where thousands of tons of soybeans are lost each year. In these places, the volunteer soybean plants remain alive, green, many vegetating and hosting, multiplying the rust fungus throughout the off-season. For ten years, there have been warnings about the regions where rust is present, its level of activity and its ability to cause the disease (infectivity). These alerts are initially propagated on social networks (Facebook: Wanderlei Dias Guerra) and later by the press and Aprosoja. In recent years, the most important alerts are for the plants that survive, many of which appear to be cultivated, in the state's cities. Some municipalities have accepted the challenge, deploying their staff to uproot the soybean plants. Other managers of important cities seem not to worry. Have they forgotten the recent past? Thus, the first case of rust was detected in Mato Grosso, on 16/09, in the urban area of ​​Primavera do Leste.

Other alerts are made when rust arrives on commercial crops, all communicated on the Embrapa Anti-Rust Consortium website. The next Alert occurs at the time of harvesting the first areas, those with early soybeans. These areas, normally harvested in December and January, despite the obligation to carry out at least two sprays against rust, one in R5.3, are cause for concern, as rust spores can spread through the action of harvesters and infect neighboring areas, which were sown later.

Currently, work is being done to harmonize the periods of sanitary emptiness between the states, something fundamental as far as possible, always observing the climatic conditions of each region. In a recent meeting with the soybean-producing federation units promoted by the Mapa Department of Plant Health, everyone agreed with this need. It is also worrying that some states still allow the planting of soybeans in the off-season, like Rondônia, for example. The disaster of this practice has already been proven. Mato Grosso felt this in the worst possible way. In addition to prolonging the permanence of rust spores in the environment for more months, it greatly increases the sources of inoculum for the following harvest, including neighboring states. It also accelerates the loss of efficiency of fungicides, few of which are already very effective, as demonstrated by the results of network trials coordinated by Embrapa Soja. It is the spores that are not controlled by the countless extra applications, necessary in off-season plantings, that survive. The fungus that is least sensitive to fungicides remains in the guax, the most resistant, the one that will be more difficult to control each year, increasing production costs and reducing the productivity of the main harvest. A shot at the heart of the activity!

Wanderlei War Days

Article published in issue 209 of Cultivar Grandes Culturas.