Seedling Diseases

Amy Timmerman, Extension Educator Author

11/22/2022 Added

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Heavy rains and cool soils throughout the state may favor the development of seedling diseases, which could impact corn and soybean emergence.

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[00:00:00.880]Nebraska Extension Ag Update with Amy Timmerman
[00:00:03.790]Heavy rains and cool soils throughout the state
[00:00:06.020]may favor the development of seedling diseases,
[00:00:08.820]which could impact corn and soybean emergence.
[00:00:11.530]These conditions come at a poor time in crop development
[00:00:14.390]as they favor several of the most common
[00:00:16.390]and damaging seedling diseases.
[00:00:18.390]As these conditions continue, be sure to monitor
[00:00:21.270]seedling emergence and stand establishment
[00:00:23.930]to detect potential problems as early as possible.
[00:00:27.170]Corn and soybean crops suffer from several common
[00:00:29.970]soil fungal and fungal-like organisms.
[00:00:32.450]These pathogens include Pythium, Fusarium and Rhizoctonia.
[00:00:35.850]Soybeans face an additional threat from the fungal-like organism Phytophthora.
[00:00:40.220]While all four of these pathogens are common, they often result in
[00:00:43.940]some form of pre- or post-emergence damping off, which can be difficult
[00:00:47.800]to differentiate during diagnosis.
[00:00:51.420]Many management options may be the same for these pathogens,
[00:00:54.610]however, some seed treatments work best for control of specific pathogens.
[00:00:59.200]These symptoms are also easily confused with
[00:01:02.110]insect injury, herbicide damage, planting problems,
[00:01:05.170]or environmental stresses that often cause similar symptoms.
[00:01:08.460]A proper diagnosis may be beneficial for more
[00:01:11.750]targeted management in the next growing season.
[00:01:14.630]Wet conditions are favorable for Pythium,
[00:01:17.640]which is our most common seedling disease of soybean in Nebraska.
[00:01:21.280]Cooler soil temperatures will make this worse as the seedling
[00:01:24.510]will be stressed and grow more slowly.
[00:01:26.920]Typical symptoms of Pythium will include seed decay,
[00:01:29.720]pre-emergent seedling rot, and seedling damping off after emergence.
[00:01:34.624]If the seedling has emerged, it often can have a root system where the outer
[00:01:39.644]layer can be easily pulled off and the center of the root will stay intact.
[00:01:45.139]In corn, dark lesions may develop on the mesocotyl or root system.
[00:01:51.133]Rhizoctonia Root Rot is favored by drier conditions and will
[00:01:55.133]occur more commonly in sandy or well-drained loamy soil types.
[00:01:59.133]On soybeans and corn, Rhizoctonia will be evident as reddish-brown lesions
[00:02:03.683]on the lower stem (typically at that soil level).
[00:02:07.683]In corn, seedlings may die and rot below the soil surface.
[00:02:11.636]These plants are often characterized by water-soaked and dark mesocotyl tissue
[00:02:16.052]that can be removed revealing the whiter inner vascular tissue.
[00:02:20.869]Fusarium is commonly favored by dryer conditions and
[00:02:24.629]in sandy or well-drained loamy soil types.
[00:02:27.709]Infected soybean crops will have stunted
[00:02:29.919]plants with brown to black discoloration
[00:02:31.999]on the roots (often in the lower portion of the root system).
[00:02:35.179]In corn, root systems may appear small with brown to black discoloration.
[00:02:39.179]Phytophthora – which is only found in soybeans
[00:02:42.859]is seen more frequently when soil conditions warm up
[00:02:45.779]because heavy rains are more common.
[00:02:47.924]Fields will typically have a history of this disease,
[00:02:51.214]which will flare up when rain events saturate soil profiles.
[00:02:55.084]Phytophthora is often observed when a field was planted with
[00:02:58.294]with a standard rate of seed treatment
[00:03:00.631]but still has significant stand reduction when wet conditions occur.
[00:03:04.968]This will be a field-specific issue and usually does not occur
[00:03:08.901]as often as Pythium.
[00:03:11.208]Typical symptoms of Phytophthora are seed decay and pre-emergence
[00:03:14.838]seedling rot, and seedling damping off after emergence.
[00:03:18.421]Typical symptoms on seedlings are darkened stems at the
[00:03:21.631]base of the plant coming up from the soil line.
[00:03:24.601]When young plants are cut at the lower stem,
[00:03:27.081]often there will be a dark center to the stem.
[00:03:29.801]Phytophthora can kill plants at any stage of development,
[00:03:33.213]but Pythium typically does not kill plants much past the V5 growth stage.
[00:03:38.382]Record keeping of the type of seedling and root rots is
[00:03:42.382]critical to allow management decision to be made next year.
[00:03:45.322]If you need assistance in diagnosing seedling diseases,
[00:03:48.722]call the Holt County Extension office at 402.336.2760 and
[00:03:53.741]I will be happy to assist you.
[00:03:56.021]This has been Amy Timmerman with Nebraska Extension.

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Seedling Diseases

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