Cotrijal warns of cautious management against Asian rust

Recurrent rains and mild temperatures throughout December provided good conditions for the early development of soybeans. However, these circumstances were also favorable for Asian rust, one of the main diseases of the crop. The disease is already widespread in Rio Grande do Sul, with eight occurrences recorded to date, according to the Anti-Rust Consortium. In the region where Cotrijal operates, the disease established itself at the end of December.

“We have a disease monitoring program and we have noticed that there is a small amount of spores being collected weekly, combined with good weather conditions in several regions where the cooperative operates. And we also have the host, which is the soybean plant itself, completing the disease triangle,” explains Leodário Montemezzo, agronomist and technical disseminator at Cotrijal.

The incidence and management of rust depend on the climate of each location. In the northernmost areas of the cooperative's region of operation, which have recorded regular rainfall and continue to maintain high production potential, the humidity and temperature conditions are favorable for rust, which is inoculated and developing. In the central and southern regions, however, the prolonged lack of rain is slowing the development of rust and, as a result, the development of the disease may even cease. 

These climate differences are also decisive in defining the management of Asian rust. “For regions that have had rain in the last 10 to 15 days, we need to continue applying the products, based on triazoles, contact fungicides, protectors and also preventives to slow the spread of the disease and prevent new outbreaks. For those producers who are in regions that have gone more than 18 to 20 days without rain, it is very important that the producer be very careful about whether or not to apply fungicides and, if they decide to apply them, that this decision be made together with the Technical Department (Detec) of the cooperative so that the actions do not harm the progress of the soybeans,” recommends Montemezzo.

Phytotoxicity

This careful management approach aims to avoid phytotoxicity, that is, negative effects on plants caused by improper or incorrect applications. “We must be aware that we do need to protect crops from pathogens that can attack them, but we cannot use a tool that causes more harm and damage than the disease itself,” emphasizes the Cotrijal agronomist.

Again, the climate will determine the procedures that should be adopted to prevent phytotoxicity. In cases where soil moisture is adequate and the plants are well hydrated, the recommendation is to observe the climate conditions and maintain prior planning, preferably carrying out applications at night.

In regions where the soil is dry and the plants are dehydrated and have high evapotranspiration, management needs to be reassessed. “We may have to replace tools or even stop applying fungicides in these more critical areas,” explains Montemezzo.

Cotrijal's Detec is available for specific analyses for each location, including being able to indicate the safest times for applications.

Leak

At this stage of soybean development, the symptoms of Asian rust can be difficult to identify. The signs should be looked for in the lower leaves of the plants, where rust pustules can be identified with the help of a magnifying glass. 

Attention

Despite the severity of rust, other diseases that can also affect soybeans should be monitored. In this harvest, which began with regular rainfall and is now experiencing reduced rainfall, it is necessary to be aware of end-of-cycle diseases. “These fungi are found in the straw and soil. During the first rains, when the soybeans were in the vegetative period, they had already entered the plant. Therefore, it is important to continue some applications targeting end-of-cycle diseases so that we do not have problems at the end of the crop with these, let's say, secondary diseases,” recommends the technical disseminator at Cotrijal.

In regions with extremely dry climates, insects should be the focus, especially thrips and mites. “In areas where it was necessary to cancel fungicide applications, the producer needs to continue with insecticide management,” he concludes.