More Bacterial Diseases in Corn — Goss's Wilt and Bacterial Stalk Rot Confirmed
July 1, 2009
Goss's Bacterial Wilt and Blight
Goss's bacterial wilt and blight has been confirmed by the UNL Plant & Pest Diagnostic Clinic in samples received from Perkins and Chase counties in southwest Nebraska, with more unconfirmed reports in eastern Nebraska.
|Figure 4. Upper plant death caused by bacterial stalk rot is sometimes the first noticeable symptom.|
Figure 6. Infected plants are frequently killed and may collapse.
Goss's wilt and blight has been a problem in this area and the Nebraska Panhandle since the early 2000s. Last year was the first time the disease was confirmed in counties statewide in approximately two decades. The recent reemergence of the disease indicates that we are at increased risk this year because of the abundance of bacterial inoculum that is expected to have overwintered from recent disease outbreaks.
In addition, the recent severe weather that damaged Nebraska's corn crop in many counties is also likely to lead to disease. Wounds caused by hail, high winds, sandblasting and other problems provide the necessary infection points for the bacteria that cause Goss's wilt, as well as other bacterial diseases and some fungi.
Two symptoms often are associated with Goss's wilt and blight. The presence of dark green leaf "freckles" at the edges of lesions is the primary symptom. It is also common to see evidence of bacterial exudate or "ooze" on the leaf surfaces, giving them a glossy appearance (Figure 1).
Bacterial Stalk Rot
Bacterial stalk rot was identified in corn and sorghum in Seward County, with several other unconfirmed reports in south central and southeast Nebraska. This disease may be caused by one of several common bacterial pathogens that occur in the soil and can overwinter in crop residue. In at least one location, the disease developed approximately 10 days after a severe thunderstorm that dropped several inches of rain and some hail, leaving the plants tattered and standing in saturated soil. The bacteria can infect through either natural openings in the plant or wounds.
Figure 5. The tops of infected plants may become decayed and easily removed.
Symptoms of this disease can develop quickly. Water-soaked lesions develop first around the point of infection and can lead to decay of the stalk (Figures 2 and 3) and may eventually spread to the leaf sheaths and blades. The disease may first be evident with the death of the upper plant (Figure 4), which often can be decayed and easily removed above a certain node (Figure 5). The disease can eventually cause death and total collapse of the plant (Figure 6). This disease is often accompanied by a foul odor.
Bacterial stalk rot is often favored by high temperatures and humidity and may develop after irrigating from sources of surface water where the bacteria can survive. The disease also develops in field areas that have been exposed to flooded conditions, which is consistent with recent weather events in areas of Nebraska.
Holcus spot continues to appear in Nebraska fields. It can appear like other diseases caused by fungi, such as eyespot and gray leaf spot, but cannot be managed with foliar fungicides.
Disease Identification and Management
Unfortunately, rescue treatments are not currently available for any of these bacterial diseases. Accurate identification is critical because some early symptoms can be easily confused with those of other diseases. Because all of these diseases are caused by bacteria, we do not expect control from foliar fungicides. Be certain that your diagnosis is accurate before applying a fungicide to manage a particular disease.
To learn more about these diseases, see:
- Watch for Bacterial Diseases in Corn in the June 19, 2009 issue of CropWatch
- Plant Disease Central, the UNL Extension Plant Pathology Web site
- UNL Extension NebGuide, Goss's Bacterial Wilt and Leaf Blight of Corn, G1675
Diagnosis. If you are unsure about the identity of this or other diseases, you can submit samples to the UNL Plant and Pest Diagnostic Clinic. Instructions and sample submission forms for the UNL Plant and Pest Diagnostic Clinic are at Plant Disease Central.
Extension Plant Pathologist
UNL Plant and Pest Diagnostic Clinic