Corn Bacterial Diseases - June 6, 2024 - Amy Timmerman, Extension Educator
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- [0:00] This Amy Timmerman with Nebraska Extension and today’s Extension update.
- [0:05] Severe weather over the past two to four weeks has caused
- [0:08] excessive damage to emerging and emerged crops.
- [0:12] For the corn plants that were emerging during these events,
- [0:15] they are at higher risk of potentially developing bacterial and fungal diseases
- [0:20] due to the wounding on the leaves created by wind and hail.
- [0:24] Goss’s Bacterial Wilt and Blight is one bacterial disease to be on the lookout for.
- [0:30] The foliar stage of this disease has two major characteristics that
- [0:34] can be used to distinguish it from other diseases.
- [0:37] The first identifiable characteristic is the development of dark green to
- [0:42] black discontinuous water-soaked spots, sometimes called "freckles"
- [0:47] because of their appearance, near the edges of expanding lesions.
- [0:51] The bacteria can also create an exudate or ‘ooze' on the
- [0:55] surfaces of the leaf which is the second identifiable characteristic.
- [0:59] When dried the exudate may glisten
- [1:02] and appear shiny on the leaf surface similar to varnish.
- [1:06] The wilt phase of the disease is not commonly seen but
- [1:09] when infection occurs early in the season the probability increases.
- [1:13] In the wilt phase, this occurs when the bacteria infect
- [1:17] the vascular system and move within the plant.
- [1:20] Infection may cause discoloration of the water-conducting elements
- [1:24] and eventually a slimy stalk rot that can lead to wilting and plant death.
- [1:29] Another bacterial disease that may be seen is bacterial leaf streak.
- [1:34] This bacterial disease can infect the plant through natural openings in leaves,
- [1:38] but wind-driven rain can also allow bacteria entry into the plant tissue.
- [1:43] As temperatures increase, it is believed that the symptoms are exacerbated also.
- [1:50] Symptoms of bacterial leaf streak look very similar to other common diseases,
- [1:54] sometimes causing confusion and misdiagnoses especially early in the season.
- [1:59] Narrow stripes between leaf veins may initially look like a common fungal disease
- [2:03] gray leaf spot which is now being identified for the first time this year.
- [2:09] Lesions usually have slightly wavy edges in contract to the
- [2:13] smooth, linear lesions margins of gray leaf spot.
- [2:18] When backlighting the leaves, the lesions will have a yellow
- [2:21] “glow” or appearance to them which helps in identification.
- [2:26] Finally, common smut which is a fungal disease
- [2:29] as a high probability of having higher incidence this year.
- [2:34] Common smut has also been called boil smut due to the development of galls.
- [2:40] Following injury, spores germinated and infect plant tissue to cause the
- [2:44] formation of galls on any plant part including leaves and stalks.
- [2:49] Galls on stalks tend to be larger than those produced on infected leaves.
- [2:55] As the gall matures, large amounts of black spores are produced.
- [2:59] Galls found on stalks have been known to impact overall standability
- [3:03] of the plant thus identification is important now to allow monitoring
- [3:07] those fields later in the growing season, especially as we approach harvest.
- [3:13] For all the diseases discussed today, management options are very limited.
- [3:18] Reviewing seed catalogs on the varieties tolerance or resistance
- [3:22] to Goss’s Bacterial Wilt and Blight and/or Bacterial leaf streak are important.
- [3:29] If replanting is required for portions of fields, try to select varieties
- [3:33] with high tolerance or resistance to Goss’s Wilt in particular with
- [3:37] the weather patterns we have been experiencing so far.
- [3:40] For fields that are showing symptoms,
- [3:42] there is not pesticide treatment option available.
- [3:45] Continue monitoring of these fields for disease progression is important
- [3:49] throughout the remainder of the growing season because these plants
- [3:53] will also be stressed and more susceptible to other diseases as the season progresses.
- [3:58] If you need assistance with disease identification,
- [4:01] samples can be sent into the Plant and Pest
- [4:04] Diagnostic Clinic located on UNL's East Campus.
- [4:07] Or reach out to your local extension educator or Dr. Tamra Jackson-Ziems
- [4:12] who is the Extension Specialist focusing on corn diseases.
- [4:16] This has been Amy Timmerman with Nebraska Extension.