Test network publishes evaluation of the efficiency of fungicides to control soybean rust

During the 36th Soy Research Meeting, held on June 28th and 29th, in Londrina (PR), public attention was drawn to the presentation of the results of network trials that evaluate the efficiency of fungicides registered and in the registration phase with the Ministry of Agriculture, Livestock and Supply (Map).

Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, is the most severe disease of soybeans. In the 2016/2017 harvest, the testing network identified a drop in the efficiency of products with carboxamides - one of the newest active ingredients on the market - mainly in tests carried out in MS, PR and RS. The most critical situation was that of the trials in Rio Grande do Sul, because sowing is later and crops are affected by spores of the fungus from other regions. “For this reason, the sowing window is a problem, because the later you plant, the more fungicide the producer needs to apply”, says researcher Cláudia Godoy, from Embrapa Soja,

According to the researcher, only for products with a specific site mode of action (newer products, registered in the last decade) for rust control, 39 tests were carried out. Another 29 trials were carried out for fungicides with a multisite mode of action (available on the market for more than 30 years). “Multisites were evaluated again by the network three years ago, in an attempt to expand options for rust management. This is because newer products are having reduced efficiency due to mutations in the fungus”, explains the researcher.

For Godoy, multisites are in a range of 50% to 60% efficiency. These products are recommended for use in programs with other fungicides. “Their function is to increase the efficiency of fungicide control and delay fungal resistance to newer fungicides,” she says.

In cooperative trials, fungicides are evaluated individually, in sequential applications, to determine control efficiency. “The information must be used to determine control programs, always prioritizing the rotation of fungicides with different modes of action and adapting the programs to the sowing season”, he reinforces. “Sequential and curative applications should be avoided to reduce the selection pressure for fungus resistance to the fungicide”, he explains.

Network trials have been carried out since the 2003/04 harvest, in the main producing regions and serve as parameters for technicians and producers to establish their soybean disease management programs. The network is made up of foundations, universities, research institutions, consultants and pesticide companies.

During the Soy Research Meeting, MAPA presented the results of the reevaluation of fungicides for Asian rust, where 104 of the recommendations were suspended, leaving 26 fungicides recommended for rust. Of these 104, more than 50% of the fungicides did not present a defense in the reevaluation and were automatically suspended.

Rust management – To minimize problems with Asian rust, Godoy says that the producer must follow the recommendations for adequate management of rust, that is, use early cycle cultivars and sowing at the beginning of the recommended season, eliminate volunteer soybean plants in the off-season for during the sanitary void, monitor the crop from the beginning of crop development, use fungicides when symptoms appear or preventively and use cultivars with resistance genes

Target stain – According to Godoy, the results of the test network for controlling the target spot are very similar to those of the last harvest. “The best treatments for target spot in recent years were also the best in the last harvest. The results show a consistency in the efficiency of the best products”, he assesses.

The results of the network tests will soon be made available in technical circulars on the Embrapa Soja website.