Aug 24, 2010
Frogeye Leaf Spot is Most Expensive Disease to Hit Argentine Soy
Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.
It seems that farmers in the three main soybeans producing countries are very concerned about how fungal diseases are impacting their soybean crop. In the U.S., the main concern this growing season has been sudden death syndrome especially in Iowa. In Brazil, the biggest concern continues to be soybean rust, which is found throughout the country. In Argentina, biggest concern last growing season was a fungal disease called frogeye leaf spot. Some researchers in Argentina feel that the disease may have reduced Argentina's 2009/10 soybean crop by 4 to 5 million tons and if that was actually the case, it would be the most expensive disease in terms of lost production to have occurred in Argentine soybean fields.
Frogeye leaf spot, sometimes called Cercospora leaf spot, occurs worldwide, but is most common in warmer regions during warm, humid weather. Frogeye leaf spot is primarily a disease of foliage, but stems, pods, and seeds may also be infected. The diseases is caused by the fungus cercospora solina. Young leaves are infected more rapidly than older leaves; with adequate moisture, new leaves become infected as they develop, until often all the leaves of the plant are infected. Reaction of different soybean varieties to the disease varies from immunity to highly susceptible.
The recommended methods of control include: grow adapted resistant varieties, plant high-quality seeds relatively free of the pathogen, rotate soybeans with other crops for two years, treat seeds with a fungicide, apply fungicides at growth stages R2 to R3, and plow under crop residues.
Scientists in Argentina feel that the monocrop nature of soybean production in the country is a recipe for increased disease pressures. The disease is more severe in monocrop soybean production and soybean production in Argentina is more monocrop than anywhere else in the world. During the 2009/10 growing season, there were eight or nine times more soybean acres planted in Argentina than corn acreage making it impossible to rotate soybeans with corn on a yearly basis
Frogeye leaf spot probably caused more yield loss in Argentina in 2009/10 than any other disease in the history of soybean production in the country. Frogeye leaf spot is not a disease that appears near the end of the soybean growth cycle. It can appear early and spread explosively. The disease can be controlled chemically, but it's not cheap or easy to do.