Feb 04, 2010
South American Soybean Crops Face Increased Disease Pressure
Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.
Soybean produces in both Brazil and Argentina have spent additional time and money this growing season battling increased disease and pest pressures. While most of the news has been about the increase of soybean rust in Brazil, Argentine farmers have also been confronting their own fungal disease.
The fungal disease that is worrying Argentine farmers is called frogeye leaf spot, which is a disease caused by fungus cercospora. The disease is found worldwide, but it is more common in warmer regions during warm, humid weather. The heavy rains that broke the back of a two-year drought in Argentina also created a favorable environment for the spread of the disease. Last year, the disease was primarily found in southern Cordoba, but this year, the disease is common throughout the heart of the soybean-growing region.
Frogeye leaf spot is primarily a disease of the foliage, but stems, pods, and seeds may also be infected. The fungus survives as mycelium in infected seeds and infested soybean debris. If left untreated, yields of susceptible varieties may be reduced by 12 to 15%. The best way to control the disease is to plant resistant varieties, rotate soybeans to other crops for two years, treat seed with fungicides, apply fungicides at growth states R2 to R3, and to plow under crop residues.
While important in local areas, frogeye leaf spot is not nearly as worrisome as soybean rust. Soybean rust first appeared in Brazilian soybean fields in 2001 and two years later it reduced the Brazilian soybean crop by 4.6 million tons. The worst year for soybean rust in Brazil was the 2003-04 growing season when the disease reduced the Brazilian soybean production by 8%. During the 2008-09 growing season, there were relatively few cases of soybean rust in Brazil, yet Brazilian soybean farmers spent US$ 1.7 billion on fungicides and Embrapa estimates that the disease reduced the 2008-09 crop by 0.5 million tons.
Currently there are over 1600 confirmed cases of soybean rust in Brazil and farmers have greatly increased the number of fungicide applications. Farmers who last year applied 2-3-4 fungicide applications are applying 4-5-6 applications this year in order to keep the disease in check.