Figure 1a. Dark “freckles” associated with Goss’s wilt lesions on corn (Figure 1a), may be more evident in leaves that are backlit by the sun or other bright light (Figure 1b). This symptom is a diagnostic characteristic of Goss’s bacterial wilt and blight, which is already occurring in some Nebraska corn fields.
July 10, 2013
Goss’s Wilt in Scattered Areas across Southern Nebraska
This week Goss’s bacterial wilt and blight was confirmed in numerous corn samples from southwest to southeast Nebraska. Plant wounding due to recent severe weather and a history of widespread Goss’s wilt across the state are likely to blame for the seemingly early development of the disease in corn fields again this year.
Figure 2a (above) and 2b. Glossy bacterial “ooze” on the upper and/or lower surfaces of leaves with large lesions can be another sign that plants have Goss’s bacterial wilt and blight.
This disease can develop any time during the growing season and during any corn growth stage. Yield impact worsens the earlier it develops and the more leaf area that is affected by lesions. Disease development now on susceptible hybrids could have devastating impacts on yield if the disease continues to worsen in those fields. At this point, the most severely affected fields are those planted with susceptible dent corn hybrids or popcorn, which is often susceptible.
Goss’s wilt does not appear to be widespread at this time, but scouting is recommended, particularly in high risk fields, to determine if it is present and to what extent. In addition, a few corn plants have been systemically infected by the bacterium, which can ultimately lead to plant death, stand loss, and greater yield loss. Systemic Goss’s wilt can develop even in resistant hybrids that have been wounded substantially.
When scouting fields for Goss’s wilt, pay special attention to:
- hybrids that are sensitive to Goss’s wilt, including popcorn,
- fields with a recent history of the disease, and
- fields with injured plants (due to hail, high winds, sandblasting)
Two key features of this disease can aid in diagnosis:
- Freckles — Also known as discontinuous water-soaked spots, these “freckles” appear as small dark green to black spots on the edges of spreading lesions (Figure 1a). While some lesions may lack this symptom, those expressing it most likely have Goss’s bacterial wilt and blight, as it is the only known pathogen to cause the symptom. Freckles may be more evident when backlit by bright light, such as the sun (Figure 1b). But, be careful to avoid confusing these “freckles” with the development of secondary fungal growth in the centers of lesions that give the surface a dusty appearance as they grow and produce spores on dead leaf tissue.
- Ooze — Also known as bacterial exudate, “ooze” occurs when bacteria are secreted on the surface of lesions. When fresh, the ooze may appear sticky and brown, but once dry, it gives the leaf a glistening or sparkling appearance (Figure 2). Be sure to check the bottom side of the leaf carefully, as well, as the exudate may be washed away by rainfall or overhead irrigation.
Identifying both of these characteristics is a likely indication that the plant has Goss’s bacterial wilt and blight. To test for Goss’s wilt, samples can be submitted to the UNL Plant and Pest Diagnostic Clinic.
The most effective disease management is with the selection and use of Goss’s wilt resistant hybrids and crop rotation to reduce the amount of overwintering inoculum (bacteria). However, several products are being evaluated in an effort to identify ways to reduce losses due to the disease.
Some bactericides are labeled for use in corn, but limited testing has been completed on corn and the Goss’s wilt pathogen. However, when considering the application of these or any pesticides, consider that some products are contact products that will not be absorbed and moved systemically in plants. Therefore, contact products are unable to provide curative activity for the infections that are already inside plants. (This is in contrast to many foliar fungicides used more commonly on corn that are systemic and provide both curative and protective activity against fungal diseases like gray leaf spot.) Contact products can provide protection from new infections for one or more weeks, but will be washed off by rainfall or overhead irrigation. Some products also may be cost prohibitive, particularly considering that they may require multiple applications for long-term protection of leaves. However, a timely application(s) may be of value in slowing disease progression.
The results of the 2009 Goss’s Wilt Management trial are posted in a June 8, 2012 Crop Watch article. The positive results were from corn plots that had just been inoculated with the bacteria causing Goss’s wilt. The treatments were applied immediately prior to or within 24 hours after inoculation. No symptoms were present at the time of application and no results are available from trials where treatments were made after lesion development.
Goss’s Wilt was confirmed in western Nebraska, northeast Colorado, and southeast Wyoming about 2006. Since then it has been confirmed in more than 60 Nebraska counties and has become important in Iowa, Illinois, and Indiana. The disease also has been confirmed in Ontario and Manitoba provinces in Canada, and as far south as the northern panhandle of Texas and Louisiana.
For the safety of yourself and others, and for the most effective results, read and follow the most recent pesticide label instructions.
For more information see:
- Goss’s Bacterial Wilt and Leaf Blight of Corn, UNL NebGuide G1675.
For information on Goss’s wilt and other corn diseases, their identification and management,
- see the UNL Extension Plant Pathology team’s website, Plant Disease Central,
- CropWatch (see Disease Management section for each crop, including corn diseases,)
- contact your local UNL Extension Educator.
Extension Plant Pathologist
Plant and Pest Diagnostic Clinic Coordinator