Transcript Black Leg of Geranium

Diseases Covered
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Rhizoctonia Crown Rot and Blight
Botrytis Blight
Black Spot
Daylily Rust
Rhizoctonia crown and root rot.
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Caused by Rhizoctonia solani
Root rot may develop either in the rooting cube
or on rooted cuttings transplanted to pots as
the crop is finished for retail. Infected roots
become water-soaked then brown.
Both root tips and sections of the root away
from the tip may develop symptoms. Crown rot
can develop on the stem as lesions expand from
stem infections occurring during propagation.
Rhizoctonia crown and root rot.
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Stem lesions may develop at a much slower pace on rooted
plants, since this tissue is more hardened off and thus more
resistant than stems of newly made cuttings.
Foliar symptoms of crown and root rot include chlorosis, leaf
necrosis, wilting, defoliation, and plant death, but often the
most common symptom is stunting.
Root rot infections may be initiated from lesions on stems or
from inoculum introduced to the potting mix from debris
surviving in the greenhouse.
Generally, moist but not wet conditions in the potting mix
favor development of Rhizoctonia crown and root rot on
potted plants.
Spacing plants with a full canopy too close together can
result in moisture and soil temperatures favorable for
development of disease due to shading of the container
surface.
Rhizoctonia – Damping off
Rhizoctonia Crown Rot –
Poinsettia
Rhizoctonia Blight – Begonia
Rhizoctonia blight – Impatiens
Control
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Control of stem and root rot begins with thorough removal
of all crop debris from the production facility at the end of
a cropping cycle.
Sanitation of work area and bench surfaces with surface
disinfectants is important.
During propagation, misting cycles should be monitored
closely to avoid over wetting foliage of cuttings once
newly made cuttings become turgid.
In greenhouse production facilities with a history of
Rhizoctonia stem and root rot, soaking dry rooting strips in
a fungicide solution can protect cuttings from disease
Generally one application of fungicide is sufficient to
protect the crop during the propagation cycle.
After transplanting, fungicide drenches may be needed at
regular intervals to prevent crown and root rot
Botrytis Blight
CAUSAL ORGANISM: Botrytis cinerea
Botrytis blight is common in all parts of the
world. This fungus is not a specific
pathogen and can take advantage of
many situations to produce a blight or rot
condition on many hosts.
It is an opportunist on cut or pruned rose
canes and will infect flowers and buds.
Symptoms/Signs
The most common symptoms usually are seen on
young flower buds which droop, turn black at
the base and later produce the cottony greyblack mycelium of the fungus.
Flowers can also be affected in the same way and
cut ends will have the black canker like
symptoms with presence of mycelium.
Cool and wet conditions facilitate grey-black
mycelial growth of Botrytis.
Botrytis Stem Canker – Impatiens,
Poinsettia
Botrytis Blight
Botrytis Crown Rot - lisianthus
Botrytis Blight – Geranium
Results from infected flowers
Botrytis Dieback - Geranium
Botrytis Blight
Disease Cycle
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This fungus is not specific and will grow on many
different plants and plant debris.
Under cool wet conditions profuse sporulation
results and spores are moved to roses by air
currents or blowing rain.
A minor wound in a bud or flower, or perhaps a
pruning cut will provide the initial point of
entry.
As the infection progresses more sporulation
results and additional sites become infected.
The fungus is a low level parasite and will
colonize wound sites as well as dead plant
material.
Control
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Prevention is the best means of control. This can be
accomplished through intense sanitation procedures.
By elimination of opportunistic colonization on dead
plant material the amount of sporulation can be
reduced.
Good ventilation is also essential in reducing disease
incidence. Some sprays may give short term relief but
the fungus usually becomes quickly resistant.
In greenhouse conditions special covers are used to
reduce the levels of ultraviolet light required by the
fungus for sporulation.
In most cases, removal of infected plant parts and
protection of wounds by chemicals is all that can be
done until warmer and dryer conditions prove too
unfavorable for continuing disease.
Black Spot
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Caused by the fungus Diplocarpon rosae.
The disease can cause almost complete
defoliation of bushes by early fall.
It produces a weakened bush on which
cane dieback, stem canker, and winter
injury can become severe.
Symptoms
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Circular black spots ranging from 1/16 inch to
1/2 inch in diameter appear generally on leaves’
upper sides.
The spots are frequently surrounded by a yellow
halo. Infected leaves characteristically turn
yellow and fall prematurely.
This leaf spot can be distinguished from others
by the fringed margin and consistently black
color.
Cane infection produces a reddish-purple spot.
In many varieties, pale flower color is indirectly
caused by infection.
Disease Cycle
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Black spot is spread by splashing water.
Infection occurs after leaves are wet for
several hours.
Therefore, the disease is more serious
during periods of rainfall.
Control
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A preventive program for black spot should begin
with a thorough cleanup in the fall. Diseased leaves
on the ground should be raked and destroyed.
All diseased canes should be pruned off by cutting
several inches into good wood.
A fungicide program should start in the summer
just before leaves become spotted. From then until
frost, the leaves may require a protective fungicide
coating. When the leaves are growing rapidly or
during rainy weather, it may be necessary to spray
the plants two times a week.
However, if growth is less rapid and rains are less
frequent, spraying at 7 to 10 day intervals is usually
sufficient
Daylily Rust
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Daylily rust is caused by the fungus Puccinia
hemerocallidis and affects the leaves and scapes.
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It is not a new disease of daylilies, having been
reported previously in China, Taiwan, Korea, Japan and
Russia.
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Unfortunately, the disease has now arrived in North
America, and was first identified in the southeastern
United States in August 2000. Because of widespread
shipping of infected plants, by late 2001 daylily rust
had been identified in approximately 30 US States,
Canada and Australia. In nature, however, the main
method of rust spread is by wind borne spores
Daylily Rust
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While daylily rust may kill the foliage on some
cultivars, it is unlikely in the short term to
actually kill the infected plant. However, it is
not yet known what the effects of continuous
infection will be on individual daylilies
Symptoms
Symptoms and Signs
Symptoms and Signs
Disease Cycle
Disease Cycle
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It is not known where the rust overwinters.
It has successfully overwintered in some States of USDA
Hardiness Zone 7 and milder as of April 2002 .
There are three possible ways that this rust may survive
the winter.
The first is as urediospores, the orange powder produced
from the spots (known as pustules) on daylily leaves.
Some rusts overwinter as mycelium (the strands which
form the body of the fungus inside the leaf) but this can
only take place where the plant tissue remains alive.
The third means by which rusts can overwinter is in the
form of teliospores.
Disease Cycle
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Teliospores are typically hardier and more durable than
the urediospores and lie dormant on dead daylily leaves
over winter.
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These new spores must be transported by the wind or other
means to a plant of the alternate host, Patrinia, which is a
perennial plant also of Asian origin. Thus it is possible that in
climates where the rust cannot survive the winter as mycelium
or urediospores, it may still be able to continue the infection in
the subsequent year if there is a plant of Patrinia in the vicinity.
Patrinia is not common at the moment in North America,
but several species are being offered for sale both as
plants and seeds. Not only does it pose a threat to
daylilies as far as overwintering of the rust is concerned,
but the rust life cycle stage on Patrinia is a form of
sexual reproduction which may increase the chances of
new races of daylily rust developing.
Control
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Cultivar selection
It is generally recommended to remove the
foliage from all plants discovered to have rust,
cutting just above the soil level.
Fungicide applications mancozeb,
chlorothalonil, azoxystrobin and triadimefon
Overhead watering should be avoided wherever
possible