October 16, 2012

Brazilian Farmers Warned not to be Complacent with Rust Control

Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.

Farmers in Brazil are being alerted to the possibility of an early onset of soybean rust in their 2012/13 soybean crop. They are being cautioned not to be complacent concerning fungicide applications especially for their early maturing soybeans. They are being advised to be ready to apply at least two applications of fungicides on their early maturing soybeans in order to minimalize any potential losses from the disease.

Soybean producers in Brazil are generally not as concerned about rust on their early maturing soybeans as compared to the later maturing varieties because of the short growth cycle. Normally, the disease does not appear in the fields until the early maturing soybean varieties are approaching maturity. Brazilian scientists are warning that the disease may appear earlier this growing season due to the fact that live rust spores have survived the shortened dry season and have been detected in central Brazil.

The three conditions that are favorable for the spread of rust include: high relative humidity, the presence of live rust spores in the air, and frequent rainfall. The first two conditions are already present in Mato Grosso. The relative humidity in the air has been increasing over the last month as scattered showers increase across the state and researchers from the state department of agriculture have identified live rust spores on volunteer soybeans growing along the sides of the highways in the state and around storage facilities. The one thing missing at the present time is frequent rainfall, but showers will become more prevalent as the rainy season takes hold.

If early maturing soybeans are infected with rust when they are being harvested, the yield losses for the early maturing soybeans may be minimal, but the actual process of harvesting can disperse the spores to nearby fields of later maturing soybeans that are still developing. The rust spores are blown out the back of the combine during the harvest process and since they are very light, they can float easily to nearby fields where the soybeans are still developing.

Early maturing soybeans in Brazil are generally harvested during the month of January, which coincides with the peak of the rainy season. Therefore, the spread of the disease into later maturing soybeans can be very rapid at this time of the year. This can result in severe infestations in later maturing soybeans which can be very difficult to control especially during periods of heavy rainfall.