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
- [00:00:18.390]As these conditions continue,
be sure to monitor
- [00:00:21.270]seedling emergence and
- [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
- [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,
- [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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