Sep 26, 2014

Live Rust Spores Found on Volunteer Soybeans in Mato Grosso

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

Planting of the 2014/15 soybean crop in the state of Mato Grosso has been underway for less than two weeks and Brazilian researchers have already identified three locations in the state where soybean rust is currently active. At all three locations, the live rust spores were found on volunteer soybeans that had germinated along the side of fields.

The disease was found on September 18th in the municipality of Campo Verde in eastern Mato Grosso and on September 24th in the municipalities of Sapezal and Campo Novo do Parecis in western Mato Grosso. The scientists noted that the infected plants at Campo Novo do Parecis were found along the side of a field where 7,000 hectares of soybeans will be planted (17,300 acres).

Even though the disease was not found in newly planted soybeans, having it in volunteer plants right alongside of the fields is important. These plants are sources of live spores that could easily move into fields of newly planted soybeans over the next several weeks. As a result, scientists are advising farmers in the region to closely monitor their soybeans and to apply a preventative application of fungicides before the soybeans start to flower.

This is the exact scenario that scientists had warned about earlier in the year when some farmers in the state decided to plant a second crop of soybeans following the harvest of their first crop of soybeans. The soybean harvest in Mato Grosso is usually complete by March and any soybeans spilled during harvesting process generally germinate soon thereafter, but the plants do not survive the dry season and die long before the new crop is planted starting in September.

This year was different. There were an estimated 120,000 hectares of safrinha soybeans planted in the state as a second crop following the harvest of the first crop of soybeans. These safrinha soybeans were harvested in May and early June. Spilled soybeans from the safrinha harvest germinated in June and July and it is those plants that are now harboring the live rust spores. A wetter than normal dry season allowed these volunteer soybeans to continue developing during July and August and they are now in the reproductive phase, which is ideal for rust development.

At a meeting this past August of the Plant and Animal Sanitation Agency of the state of Mato Grosso (Indea/MT), there was unanimous agreement that the 90-day soybean free period in the state should be expanded to 150 days. Instead of prohibiting the existence of live soybean plants starting on June 15th and ending on September 15th, the scientists agreed that it should start on April 15th and end on September 15th. The agency is still formulating the proposed new rules and they have not yet made an official announcement of the change.

If the new rules are adopted, it would eliminate the possibility of planting safrinha soybeans in the state because there would not be enough time for a second crop of soybeans to mature before the prohibition period starts.