Seedling Diseases - July 6, 2022 - Amy Timmerman, Extension Educator
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- [0:00] Nebraska Extension Ag Update with Amy Timmerman
- [0:03] Heavy rains and cool soils throughout the state
- [0:06] may favor the development of seedling diseases,
- [0:08] which could impact corn and soybean emergence.
- [0:11] These conditions come at a poor time in crop development
- [0:14] as they favor several of the most common
- [0:16] and damaging seedling diseases.
- [0:18] As these conditions continue, be sure to monitor
- [0:21] seedling emergence and stand establishment
- [0:23] to detect potential problems as early as possible.
- [0:27] Corn and soybean crops suffer from several common
- [0:29] soil fungal and fungal-like organisms.
- [0:32] These pathogens include Pythium, Fusarium and Rhizoctonia.
- [0:35] Soybeans face an additional threat from the fungal-like organism Phytophthora.
- [0:40] While all four of these pathogens are common, they often result in
- [0:43] some form of pre- or post-emergence damping off, which can be difficult
- [0:47] to differentiate during diagnosis.
- [0:51] Many management options may be the same for these pathogens,
- [0:54] however, some seed treatments work best for control of specific pathogens.
- [0:59] These symptoms are also easily confused with
- [1:02] insect injury, herbicide damage, planting problems,
- [1:05] or environmental stresses that often cause similar symptoms.
- [1:08] A proper diagnosis may be beneficial for more
- [1:11] targeted management in the next growing season.
- [1:14] Wet conditions are favorable for Pythium,
- [1:17] which is our most common seedling disease of soybean in Nebraska.
- [1:21] Cooler soil temperatures will make this worse as the seedling
- [1:24] will be stressed and grow more slowly.
- [1:26] Typical symptoms of Pythium will include seed decay,
- [1:29] pre-emergent seedling rot, and seedling damping off after emergence.
- [1:34] If the seedling has emerged, it often can have a root system where the outer
- [1:39] layer can be easily pulled off and the center of the root will stay intact.
- [1:45] In corn, dark lesions may develop on the mesocotyl or root system.
- [1:51] Rhizoctonia Root Rot is favored by drier conditions and will
- [1:55] occur more commonly in sandy or well-drained loamy soil types.
- [1:59] On soybeans and corn, Rhizoctonia will be evident as reddish-brown lesions
- [2:03] on the lower stem (typically at that soil level).
- [2:07] In corn, seedlings may die and rot below the soil surface.
- [2:11] These plants are often characterized by water-soaked and dark mesocotyl tissue
- [2:16] that can be removed revealing the whiter inner vascular tissue.
- [2:20] Fusarium is commonly favored by dryer conditions and
- [2:24] in sandy or well-drained loamy soil types.
- [2:27] Infected soybean crops will have stunted
- [2:29] plants with brown to black discoloration
- [2:31] on the roots (often in the lower portion of the root system).
- [2:35] In corn, root systems may appear small with brown to black discoloration.
- [2:39] Phytophthora – which is only found in soybeans
- [2:42] is seen more frequently when soil conditions warm up
- [2:45] because heavy rains are more common.
- [2:47] Fields will typically have a history of this disease,
- [2:51] which will flare up when rain events saturate soil profiles.
- [2:55] Phytophthora is often observed when a field was planted with
- [2:58] with a standard rate of seed treatment
- [3:00] but still has significant stand reduction when wet conditions occur.
- [3:04] This will be a field-specific issue and usually does not occur
- [3:08] as often as Pythium.
- [3:11] Typical symptoms of Phytophthora are seed decay and pre-emergence
- [3:14] seedling rot, and seedling damping off after emergence.
- [3:18] Typical symptoms on seedlings are darkened stems at the
- [3:21] base of the plant coming up from the soil line.
- [3:24] When young plants are cut at the lower stem,
- [3:27] often there will be a dark center to the stem.
- [3:29] Phytophthora can kill plants at any stage of development,
- [3:33] but Pythium typically does not kill plants much past the V5 growth stage.
- [3:38] Record keeping of the type of seedling and root rots is
- [3:42] critical to allow management decision to be made next year.
- [3:45] If you need assistance in diagnosing seedling diseases,
- [3:48] call the Holt County Extension office at 402.336.2760 and
- [3:53] I will be happy to assist you.
- [3:56] This has been Amy Timmerman with Nebraska Extension.