Last week, I received an email from Tamara Jackson, Extension Plant Pathologies that they’ve received confirmation from a colleague in the Pioneer lab in Iowa and Kevin Korus in our UNL Plant & Pest Diagnostic Clinic, which confirmed southern rust in 2 samples from Fillmore County. Both came from irrigated fields and the incidence and severity were low, but this is certainly something we will need to be on the lookout for.
Since then, southern rust has been confirmed in Adams, Clay, Hall and Thayer Counties as well in south central Nebraska and Burt County in northeast Nebraska. Warm temperatures and high humidity may promote the development and spread of disease.
Tamara indicates that “Southern rust is an aggressive pathogen and can spread and worsen very quickly at optimal temperatures and with humidity and moisture to support infection. The warm night temperatures and high humidity likely are to blame, as well as the outbreak of the disease in southern states from which our spores probably originated. In addition, we have had recent development of common rust, which is much less damaging and concerning, but may create some confusion when making diagnoses in the field. While the color of the spores/pustules can be different, this is really an unreliable and difficult characteristic to use to differentiate the diseases. Southern rust (tan to orange color) tends to sporulate predominately on the UPPER leaf surface, and common rust (red to brown) sporulates equally well on BOTH leaf surfaces.”
She indicated that the most reliable way to tell them apart is in the laboratory with microscopic examination of the spores, which UNL’s Diagnostic lab is able to do quickly, so she recommend submitting samples to the UNL P&PDC for identification.
Tamra and other colleagues have submitted an article with several other timely cropping updates that are posted on the CropWatch website. Also check out our NebGuide “Rust Disease of Corn in Nebraska”.
So, now’s the time to be scouting those fields for gray leafspot as well as rust diseases and making decisions based on current recommendations. Check out the Gray leafspot NebGuide.