August 8, 2013

Southern Rust

Southern rust (Figure 1) of corn has been confirmed in 11 Nebraska counties and likely is present in others as well. In most areas, the disease severity has not changed dramatically. However, some southern Nebraska locations are reporting a rapid increase in the disease.

Unseasonably cooler temperatures are less than optimal for the fungus and may have slowed the spread of the disease in much of Nebraska. However, recent rainfall and increased humidity will likely support more southern rust development, especially if temperatures hover in the upper 70s and lower 80s, ideal temperatures for southern rust development.

Continue to scout and monitor for early evidence that the spores are infecting corn plants, such as the sudden development of new, small yellow flecks on leaves (Figure 2). These flecks can be an indication of early disease development, such as rusts, and may help anticipate an increase in disease and potential need for fungicide application.

Hail- and Wind-Damaged Corn

Figure 3. Hail bent and stripped this corn in Clay County in and Aug. 1 storm.  (Photo by Jenny Rees)

Weather events during the last few days have caused moderate to severe damage to Nebraska’s corn crop in many areas of the state (Figure 3). Many growers are considering fungicide applications on damaged corn.

The results from experiments conducted on injured corn to simulate hail injury have led to conflicting results. Results reported from experiments conducted at the University of Illinois did not show consistent benefits with fungicide use. However, preliminary results from the first year of experiments at Iowa State University in 2012 were favorable for fungicide use following simulated hail injury, particularly when applications were made seven days versus two days after damage. These results are summarized in previous CropWatch articles:

• Fungicide Use in Corn After Hail Events and Prior to Tasseling (UNL CropWatch, June 25, 2010)
   
• Hail and Fungicides Update 2013 (ISU Integrated Crop Management News, July 17, 2013 ) 

Damaged Corn – What’s Next?

Unfortunately, secondary disease problems commonly develop in corn that has been damaged by wind, and especially hail. The wounds created facilitate infections by pathogens that can lead to the development of Goss’s bacterial wilt and blight, common smut, stalk rot diseases, ear rot diseases, and others. Scouting for diseases in damaged corn is important to anticipate future problems and better manage them.

Quick Guide to Diseases and Management

• Goss’s wilt — Crop rotation to non-host crops and selection of resistant corn hybrids will reduce disease severity next year(s)
   
• Common smut — No management needed or available, may produce large quantities of black spores in mushroom-like galls
  
  
• Stalk rot diseases — Harvest corn early in affected fields before lodging occurs.
   
• Ear rot diseases — Watch for ears with discoloration and/or obvious fungal growth inside and/or on husks. Storage is not recommended as ear rot diseases can lead to development of grain mold in the bin. Short-term storage may be possible if corn can be dried to less than 15% moisture.

For help in diagnosing southern rust or other plant diseases, submit samples to the UNL Plant and Pest Diagnostic Clinic or contact your local UNL Extension office.

Tamra Jackson-Ziems
Extension Plant Pathologist
Kevin Korus
Plant and Pest Diagnostic Clinic
Jennifer Rees
UNL Extension Educator in Clay County