Dec 18, 2009
Heavy Rains In Southern Brazil Evoke Fears Of Severe Outbreak Of Soybean Rust
Author: Michael Cordonnier/Soybean & Corn Advisor, Inc.
A stalled out frontal system brought heavy rains across the state of Parana this week resulting in numerous downed trees and flooded fields. The western and northwestern parts of the state were hardest hit and this is the primary area of soybean production in the state. While abundant moisture is advantageous for soybean production, it is also ideal for the spread of soybean rust. Since soybean rust was discovered in Brazil in 2001, the disease has cost Brazilian soybean producers at least US$ 13 billion dollars in extra production costs and lost productivity. If left untreated, the disease can result in losses of up to 90%.
The 2009-10 growing season in Parana has been very wet, which allowed the disease to move into commercial soybean fields a month earlier than in previous years. Embrapa has already identified 175 cases of rust in Brazil (up from 101 cases three days ago) with 35 of those cases being reported in Parana. According to Claudia Godoy, a researcher with Embrapa Soja, soybeans are more susceptible to the disease when the plant enters the flowering and pod-filling phase. Heavy rains are expected to continue falling in southern Brazil due to El Nino and as a result, scientists are worried that the number of rust cases could explode.
In recent years, the disease has shown less sensitivity to the usual fungicide treatments. Fungicides that were used effectively in prior years to control the disease no longer provide an adequate control. A mixture of fungicides must now be applied and the time interval between treatments has also been reduced. The fungicides used to control the disease are classified as contact fungicides, which means that they must be reapplied as new leaves emerge on the plant. The length of effectiveness of the chemical is also a function of the amount of rainfall received after the chemicals are applied. Under ideal conditions, each application may be effective for 25 to 35 days. During periods of heavy rainfall, each application may be effective for less than 25 days.
Timing of the treatments is critical for adequate control of the disease. Only a few days delay in applying the fungicide due to inclement weather or wet field conditions can result in lost yield potential.