So far this year target spots of soybean and frogeye leaf spot have both been identified in North Carolina. Many cultivars are resistant to these diseases so there is no cause for alarm at this time.
If the disease is detected it warrants a fungicide application. If target spot is identified it warrants an application of a strobilurin fungicide. If frogeye is identified then a combination fungicide (StrategoYLD, Headline Amp, Fortix, Quadris Top, or Affiance) may be warranted since resistance to strobilurin fungicides was identified last year in Beaufort County.
Soybean rust (SBR) has been identified in a soybean sentinel plant in Alabama. This is in Prattville Ala., which is just northwest of Montgomery. Soybeans were at R5 and 100 percent canopy closure. Aside from Alabama , SBR appears to be restricted to Mexico, the Gulf Coast, and North Central Florida at this time. SBR has not been found in Georgia as of this writing.
At this time there is little risk of soybean rust in North Carolina. Severe winter conditions along much of the Gulf Coast and Florida eliminated rust survival in many areas from which it has traditionally spread.
Still, conditions during the growing season in North Carolina as well as the rest of the Southeast, air movement patterns, and lastly paths of tropical storms will be the major factors as to whether soybean rust will require management. We will continue to conduct mobile surveys for soybean rust when rust is closer. Also, soybean samples submitted to the Plant Disease and Insect Clinic will be monitored for rust.
Although southern rust of corn and soybean rust are both tropical rust fungi, they are very different organisms. SBR typically follows the same pathway as southern rust of corn, but there are considerable differences between how these two rust fungi (southern rust of corn and soybean rust) develop and move.
The primary reason southern rust of corn has moved into North Carolina at this time is due to the fact that corn is planted much earlier in Georgia and Florida than are soybeans. Furthermore, much of the large corn acreage in Georgia is irrigated which provides for a more optimal environment for rust development.
Temperatures are generally warmer when soybeans reach the reproductive stage in Georgia (as opposed to southern rust of corn). Lastly, the limited Georgia soybean acreage (usually only 200,000 to 300,000) limits the amount of SBR inoculum that is available for movement.
Some sources for more detailed information on Asiatic soybean rust and Southern corn rust are listed below:
The USDA soybean rust web site
The North Carolina Agricultural Chemical Manual