Goss's bacterial wilt and blight was confirmed in mid-July 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, according to Tamara Jackson-Ziems, University of Nebraska-Lincoln plant pathologist.
This disease can develop any time during the growing season and during any corn growth stage, she says. 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, Jackson-Ziems says to 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. 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. 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. 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.
Source: UNL CropWatch