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Seed, Nursery, and Seedling
Diseases
Seed Decay
Major Factors Influencing
Seed in Storage
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High Moisture and High Temperature
Seed stored improperly often decay. Moisture and temperature are the two
most important factors in proper seed storage: low moisture and low temperature
discourage seed decay.
Sycamore seeds with their
coats removed.
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Fungi growing on sycamore
seed after storage in a moist,
warm condition.
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Fungi cultured from sycamore seeds stored
at various temperatures.
Note the fewer colonies at the low temperature.
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Damping Off of Forest Tree
Seedlings
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Pre-emergence damping off is first seen
as poor stand development. This slide shows large areas in beds devoid
of seedlings. This most frequently is indicative of seeds or germinated
seeds killed due to infection by one of several fungi prior to emergence
from the soil.
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Post-emergence damping off.
Note how the newly emerged seedlings have
toppled over in the containers. The fungus
has infected the seedling at the ground line
causing tissue to collapse and become necrotic.
Pre- and post-emergence damping off results
in a poorly stocked stand.
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Pre- and post-emergence damping off also
can occur on hardwood seedlings
as seen with these sweetgum plants
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Top Damping off
Top damping off, although rare, is spectacular
when it occurs. In this type of damping off,
pathogens that cause pre- and post-emergence
damping off are splashed onto foliage
of older seedlings and cause necrosis of
the needles killing the plant in most cases.
Seedling Root Decay
Many of the same fungi that cause damping
off also can infect roots later in the season
causing a root necrosis that is usually first
seen as chlorotic and necrotic foliage and
stems. Examination of seedlings showing
these symptoms reveals extensive root
decay as seen on the right.
Black or Charcoal Root Rot
Major symptoms are decay of feeder
roots and hypertrophy and hyperplasia
of large roots and root collar area.
The enlarged areas become dark brown
to black.
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Compare the root systems of a healthy
seedling (left) with that of an infected
seedling (right).
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Cross section of a healthy root (left) and
an infected root (right). Note the number
and size of cortex and bark cells of the
infected root compared to the healthy root.
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Foliar symptoms as a result of
root infection. Note the fungus
has parasitized the roots not
the foliage.
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Cylindrocladium Root Rot
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Red pine
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Black spruce |
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Fraser fir
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Black walnut |
Foliage symptoms showing chlorosis, necrosis,
and defoliation.
Root and root collar symptoms on yellow poplar
(middle and right) and sweetgum (left).
Note the dark color both internally and externally.
Feeder roots are also decayed.
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Conidiophores and clumps of conidia of
Cylindrocladium
scoparium on a piece of root tissue (right) and conidia (the long slender
spores on the left).
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The left and center photos show microsclerotia
in root segments. On the right is a germinating microsclerotia. Note that
several hyphae are produced from a single microsclerotium.
Cylindrocladium Foliage Blight
Cylindrocladium spp., under the proper
conditions, can have spores rain-splashed or
blown onto foliage causing a blight.
Note the chlorosis and necrosis of the needles
on these 2-year-old white pine seedlings.
Seedling Disease Management
and Control
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The most common practice to manage soilborne
pathogens
is by soil fumigation using a methyl bromide-chloropicrin
combination. This chemical is injected in prepared beds and covered with
a polyethylene tarp for a minimum of 48 hours. Modern equipment has been
developed such that chemical injection, tarp placement and sealment of
tarp edges with a layer of soil is done in a one step operation.
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Results of soil fumigation in a nursery that
had damping off and root
decay problems. Note the untreated
beds in the foreground.
Foliar fungicides can be applied if a foliar
disease is involved.
A healthy, well managed nursery of pine seedlings.
Some photos provided by:
Russ Bullock
M. K. Beute
C. Cordell
G. Fakir
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This website was prepared by Becky Bernard.
Last updated on 04 February 2008 by M.J. Munster
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