Many credit rust's limited spread in large part to this growing season's hot, dry conditions.
David Lanclos, Louisiana Extension soybean specialist, says, "With the exception of the last couple of weeks in certain parts of south-central Louisiana, things just haven't been conducive for rust. There has to be 10 to 12 hours of dew or moisture of some sort, and that's just not happening."
Louisiana currently has a heat index hovering around 105, which Lanclos says is above the optimum temperature for the rust to get going.
Forecasters last week predicted continued hot, dry conditions over the eastern Corn Belt through early July. Long-range forecasts released by Meteorologix weather service also predicted a drier period for the central and eastern Midwest from July 4 through July 9.
Depending on the weather, USDA officials still project Asian rust could reach the Midwest by late July or early August. "It is expected that extension personnel will start finding rust in soybeans first in the southern Gulf Coast region, ...and then moving north over time, it could peak around late July, early August in the North," said Joseph Jen, USDA Under Secretary for Research, Education, and Economics in a press release in early June.
The northward spread of the windborne fungus will depend on summer storms and how quickly Southern farmers detect and treat infected fields, Jen said. "This is heavily dependent on weather factors and also whether farmers in the South control the disease with timely sprays," Jen said.
Strong winds accompanying a tropical storm, hurricane or severe thunderstorm could blast the fungus from the U.S. Gulf Coast across the continent in as little as three to five days, he added.
To track confirmed cases of Asian soybean rust visit USDA's Web site at www.usda.gov/soybeanrust. It provides detailed maps on the extent and severity of soybean rust outbreaks in the United States the Caribbean basin and Central America.