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Corn+Soybean Digest

Brazilian Soybeans And ASIAN RUST

Experienced with rust, many Brazilian farmers lay out their planted areas in a grid and check the center of each square at least every other day. They are looking for signs of rust, following advice from Embrapa, the Brazilian Agricultural Research Agency.

Embrapa stresses two other factors as well when it comes to controlling rust:

  • Other diseases may appear before rust, such as target spot (Corynespora cassiicola) or Rhizoctonia blight (Rhizoctonia solani).

  • Due to Brazil's huge size (Brazil is larger than the U.S. 48 contiguous states) and varied soil and climate types, there is no single rust identification formula that can be applied in all cases. Therefore daily scouting is needed — and not just scouting out the pickup window.

At this writing, Asian rust has already been identified in 12 out of 26 Brazilian states. Those who planted early, mostly in the first days of October, may reach harvest without seeing any rust. But with the amount of spores in the air, farmers who picked cultivars for late planting should keep a close watch.

Early detection and prompt fungicide application are the keys to combating the disease. And Brazilians know it well, as they first had to deal with Asian rust during the 2000-01 season.

Farmers paid dearly for not dealing adequately with the unfamiliar problem. According to Embrapa, an area of 540,000 acres in two Center-West townships alone suffered production losses of 30%, equivalent to $30 million.

Overall, Brazil suffered losses estimated at 570,000 metric tons, then worth some $125.5 million.

In the following season, higher than usual temperatures in most soybean regions helped to keep Asian rust at arm's length. But during the 2002-03 harvest a new rust strain brought huge losses to the states of Bahia, Mato Grosso, Goiás and Minas Gerais.

The final national tally reported a total “rust cost” of almost $1.2 billion, based on production losses of 3.4 million metric tons (equivalent to $737.4 million), and expenses with additional application of chemicals estimated at about $1.17/acre (or $426.6 million total). These numbers don't include federal and state fiscal losses, estimated at $123.2 million.

In the 2003-04 harvest, although farmers were better informed, armed and ready, the disease still caused overall losses of $2.1 billion in reduced production and $204.6 million in lost revenues for the government.

New disease strains appear every year and weather conditions help the spores reach previously unaffected areas. Also, alternative host crops, such as kudzu in Paraná state and neighboring Paraguay, help the fungus remain alive during the off-season.

Rust has become a non-stop fight of Herculean proportions for Embrapa and Brazilian farmers.

Irregular rainfall and dry spells without excessively high temperatures help the spores to travel and settle.

In other regions, continuous rain hampers fungicide spraying, especially where soybeans were planted later in the season.

Public and private laboratories must also identify pathogenic and genetic variations in fungi from different areas in the country to be able to prescribe specific combat measures.

Embrapa is telling farmers to plant as early as possible. Areas where soybeans have been planted later usually suffer more aggressive attacks, because that's when the fungi attain their highest inoculation levels.

Condensed planting will also make it harder for fungicides to reach the middle and lower thirds of plants.

Embrapa offers a few other recommendations, but the two main points are:

  1. Upon detection, each case must be analyzed separately and will probably require very specific treatment.

  2. Visit the fields beginning early in the season and do it daily.

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