Oct 06, 2009
Rains Arrive Early In Brazil And So Too Has Soybean Rust
Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.
The good news is that the rains have started early in Brazil which means a good start to the growing season. The bad news is that the rains have allowed soybean rust to start early as well in Brazil. A dozen cases of rust have been reported thus far in four Brazilian states - Mato Grosso do Sul, Goias, Tocantins, and Parana. In Mato Grosso do Sul, Goias, and Parana the disease was found on individual volunteer soybeans and in Tocantins it was found in eight irrigated seed production fields.
The only soybeans allowed to be grown under irrigation during the dry season are soybeans used in research or for seed increase. These fields are supposed to be monitored closely and sprayed regularly for rust, but it looks like the monitoring program was not completely successful in Tocantins.
As an illustration of just how early this is for soybean rust, last year the first rust was found on volunteer soybeans in the middle of November and it wasn't until December that the first rust appeared in a commercial field of soybeans. In 2008-09, dry weather delayed the start of planting and it also delayed the development of soybean rust as well.
This early start for soybean rust is something that must be monitored closely. Soybean farmers in Brazil have the means to control the disease with appropriate fungicide applications, but its not easy and its not cheap. The fungicides used to control the disease are contact fungicides, which means that they are effective for generally 25-35 days. The length of effectiveness depends on the weather after the fungicide is applied (heavy rains reduces the effectiveness) and the stage of development of the crop. If follow up treatments are not applied at the right time, significant yield losses can result.
Soybean rust first appeared in Brazil during the 2001-02 growing season and since that time it is estimated that it has cost Brazilian soybean farmers US$ 11.6 billion in lost production and chemical costs. Brazilian scientist and farmers have made great strides in controlling the disease, but in 2008-09 losses still totaled US$ 1.5 billion. Brazilian scientist have released new soybean varieties that demonstrate a level of tolerant to the disease, but complete resistance to the disease will probably never be accomplished. As new tolerance is developed, the disease mutates into new races and the cycle just continues.
As Brazilian soybean farmers refine their control methods, soybean rust will continue to be chronic problem for the foreseeable future. The control of this disease is one of the contributing factors of why the cost of growing soybeans in Mato Grosso has soared in recent years. Farmers in Mato Grosso had fully intended to grow three soybean crops a year, two would be rain-fed and one would be irrigated. The discovery of soybean rust put an end to that idea because soybean farmers could not afford to fight the disease year round. The state governments also stepped in and declared that there must be a 90-day soybean-free period in order to break the disease cycle.