Although soybean rust has not yet been observed in Kentucky this year, it is likely present in the state. Soybean rust was recently reported in southern Illinois (Union County, IL). From all observations, the Kentucky soybean crop should be at later stages of development, and soybean rust should not have any impact on yield of Kentucky soybeans. For fields with soybean plants at developmental stage R5 (beginning seed) or beyond, it would be highly unlikely that soybean rust would cause any yield loss at this time.
Monitoring the distribution and northwardly progress of soybean rust in the U.S. can be done by going to the Soybean ipmPIPE website. If soybean plants with suspicious symptoms are observed, please work with your county Extension agent to submit a sample to the University of Kentucky Plant Disease Diagnostic Lab for diagnosis.
Soybean rust can be difficult to identify, especially when it is at a low incidence and severity. Small, slightly-raised pustules can be observed on the underside of affected soybean leaflets. These pustules often are observed near a leaf vein, where dew or moisture may be retained (Figure 1.). The use of a hand lens or a dissecting microscope makes it easier to observe these pustules (Figure 2).
By Carl A. Bradley, Plant Pathology Extension Specialist