Soybean rust has been found in southeast Arkansas and west-central Mississippi, about 250 miles from southeast Missouri. Scouts in Missouri are monitoring soybean fields.
“Soybean rust has not been detected in Missouri this year,” said Allen Wrather, University of Missouri Extension plant pathologist at the MU Delta Center, Portageville. Wrather heads the Missouri scouting network monitoring soybean fields. “The weather during the next few weeks will greatly impact the spread of rust.”
Soybean rust, which survives on leaves of kudzu as well as soybean plants, was not active early this year in Gulf Coast states, where it is detected first during the growing season. Hot, dry weather, including severe drought in Texas, has kept the rust spores from spreading through the air.
“Rust survey coordinators went on high alert during recent rains,” Wrather said. While sunshine kills rust spores, rain and humid weather enhance the spread of the disease, which can defoliate soybean plants.
Soybean rust has been found in Missouri four of the last five years, but always late in September or October, near harvest.
Wet weather in Missouri this spring delayed planting. “Soybean maturity and harvest will be later than normal. Rust that develops in September might damage late-maturing soybean plans and reduce yield.”
Early detection is key to prevention. “Initial infections are microscopic pustules on the soybean leaves.”
This year, scouts are collecting leaf samples in eight monitoring fields, four in southeast Missouri and four in southwest Missouri. Scouts gather 100-leaf samples to submit to the pathology lab at the MU Delta Center. Each leaf is examined under a microscope.
In past years, the scouting network was active across the state throughout the season. The network was reduced this year when scouting funds were cut.
Scouts have intensified their survey in the past week. If rust spores move further north, fields will be monitored in central Missouri.
“Our objective is to detect soybean rust when it first starts to develop in Missouri soybean fields,” Wrather said. “If detected, farmers will be alerted.”
Fungicides are available to slow rust spread and can be applied when spores reach an area. Wrather cautions growers not to apply fungicides too early. “When spores arrive, MU Extension specialists will make recommendations on control measures and timing.”
Scouting reports from across the soybean-growing region are posted at http://www.sbrusa.net . In the past, MU pathologists expected rust to come into the Missouri on southwestern winds from Texas and Oklahoma.
For most of the 2009 growing season, prevailing winds have been from the northwest, bringing cooler than normal weather to the region. That may change with the coming hurricane season.
Five years ago, the first soybean rust was found in the Missouri Bootheel after remnants of a hurricane blew inland from the Gulf of Mexico. The 2009 tropical storm season has just begun.
Farmers and crop consultants can submit samples by express delivery to the MU Plant Diagnostic Clinic for identification. The lab charges $15 for the service. Forms and shipping instructions are available at http://soilplantlab.missouri.edu/plant/  or at local MU Extension centers.