Asian soybean rust is expected to continue in the Mid-South over the next few weeks, according to the USDA Soybean Rust website.
Currently, Mississippi is the hotspot of soybean rust.
In the second week of September, experts confirmed soybean rust in 15 Mississippi counties. So far this year, soybean rust has been confirmed in 38 counties in Mississippi.
In 2012, soybean rust has been reported in 113 counties in the US. In the Mid-South, Arkansas has had two counties; Louisiana, six.
The high level of moisture from Hurricane Isaac deposited additional soybean rust spores. At this stage of the season, write Tom Allen and Trent Irby in the August 31 issue of Mississippi Crops Update, soybean rust shouldn't be cause for alarm.
For soybean rust to develop, an incubation period of seven to 13 days before the spores land on a leaf is required. Early infection is almost impossible to detect with the eye, they point out. Once pustules are formed and spores are released the infection cycle repeats itself for the second generation of pustules and subsequent spore dispersal, an additional seven to 13 days.
Allen and Irby say soybean rust has been detected at low levels in most locations. They contrast this year with 2009, when soybean rust was easy to detect.
In soybeans at the R4 growth stage, Allen and Irby say a fungicide application might be economically beneficial in soybeans following wheat or those that were planted late. With soybean rust identified throughout the state, a pre-mix or a tank mix that contains a strobilurin plus a triazole would likely be the most beneficial.
Soybean fields at the R5 growth stage would not likely need a fungicide application. The closer a soybean plant is to R6 typically means that even if some leaf surface area is lost it will likely not have a negative impact on yield.