January 27, 2011

Scientist Advise Brazilian Farmers They Must Spray for Soy Rust

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

The later than normal arrival of soybean rust in Mato Grosso has scientists worried that soybean farmers in the state may try to save money by not applying the recommended fungicide treatment to combat the disease. They are advising farmers that this could be very risky especially for the later maturing soybeans. The yield of any unsprayed individual field may not be significantly lower than a treated field, especially if the field is close to maturity when the disease appeared, but that field could act as a huge source of disease spores for nearby fields that will mature later.

The weather in the state has turned much wetter during the month of January, which are ideal conditions for the spread of the disease. While only four official cases of the disease have been reported in Mato Grosso, researchers believe there are many more cases waiting to be confirmed. In isolated areas where the disease has been more prevalent, some losses already are estimated at 10%.

Many farmers have not applied any of the anticipated three applications of fungicides and the Mato Grosso Research Foundation (Fundacao MT) is advising farmers not to forgo preventive fungicide applications. If an infected field is harvested without having had any preventive fungicide application, the harvesting process can spread a huge amount of spores to all the neighboring fields.

The spread of the disease can be explosive especially during periods of wet weather when ground applications of fungicides may be delayed due to wet field conditions. Periods of heavy rainfall can also wash off some of the fungicide, requiring reapplications. The fungicides used to control rust are contact fungicides, which mean they need to be reapplied throughout the growing season. During normal weather conditions, one application may protect the field for 25 to 30 days. During periods of heavy rainfall, one application may protect the field for only 12 to 15 days.