Brazilian Farmers Advised to stay Vigilant about Soybean Rust

As farmers in Mato Grosso,Brazil start to harvest some of their early maturing soybeans, scientists are advising them to stay on the lookout for the presence of soybean rust and the corn earworm. Approximately 1% of the soybeans in Mato Grosso have been harvested and the harvest should peak at the end of January. Thirteen cases of rust have been reported in the state, which ranks it as third behind the states of Goias and Sao Paulo. In all of Brazil, there have been 81 confirmed cases of soybean rust, which is slightly more than the average over the last three years.

The relatively low number of rust cases in Mato Grosso has been attributed to preventative measures taken by farmers. Preventative fungicide applications should be made at pre-flowering or flowering even though the disease may not have officially been identified in the area. In addition to helping to prevent soybean rust, which is the number one threat to soybeans in Brazil, the fungicide will probably also help to control other minor fungal diseases as well. Research has shown that controlling these minor foliar diseases can result in significant yield increases.

The actual process of harvesting can increase the risk of soybean rust in neighboring fields. The soybean rust spores are very light and they can easily be dispersed by the wind over very long distances. If the field being harvested was heavily infested with rust, the combine could make huge clouds of spores become airborne dispersing them to nearby fields. Soybeans are more susceptible to rust infestations when they are in the flowering stage and it is entirely possible that while one field of soybeans is being harvested, the field next door may still be flowering or filling pods, making it susceptible to rust infestation.

The soybeans being harvested are early maturing soybeans (90-100 day maturity) that were planted as soon as the 90-day soybean free period ended last September 15th. But while these soybeans are being harvested, nearby fields may have been planted in October with full maturity soybeans (120 day maturity) and these fields may still be flowering or in mid-pod fill.

Farmers are also advised to check their fields at least once a week for the presence of the corn earworm. Thus far, farmers have been generally successful in keeping the insect populations below the economic threshold.