A.R. Chase
is a Plant Pathologist and President of Chase Research Gardens, Inc.
C.R.G. is a private research and consulting corporation specializing in
ornamental plants.
Both hourly and contract services are available.
You can reach C.R.G. at P.O. Box 168, Mt. Aukum, CA 95656 Phone and Fax:
916-620-1624 - E-mail: MTAUKUM@AOL.COM
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Bacterial
blights and stem rots
Pathogen - Erwinia carotovora subsp. carotovora or E. chrysanthemi
Symptoms - Bacterial blight is typified by watery leaf spots
with centers that fall out. Bacterial stem rots caused by Erwinia
spp. are generally first noticed when cuttings are stuck. The cut
end of the stem becomes mushy and foul smelling and the rooting process
stopped. The leaves on infected cuttings usually yellow quickly.
Control - Control of bacterial leaf spots or blights can be
best accomplished through use of clean propagation material and a
watering system that either does not wet the foliage or allows it
to dry rapidly. Both antibiotic and copper compounds provide little
control of bacterial diseases and are not recommended. Bacterial stem
rot is usually not possible to control once started. Use of clean
cuttings is the only successful method of cultural control although
some growers have reported dipping in Agri-Strep as a moderately successful
control method. |
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Xanthomonas
leaf spot
Pathogen - Xanthomonas campestris pv. dieffenbachiae
Symptoms - Reddish-brown areas with bright yellow margins form
on leaf edges are the most common symptom. Under wet and warm conditions,
bacteria also spread into leaf centers and lesions expand until they
reach a leaf vein.
Control - Minimize water on leaves and use clean cuttings.
Sprays of copper or antibiotic compounds on a weekly basis provide
moderate control under some growing conditions. Be careful to use
appropriate rates of copper compounds since copper toxicity symptoms
look similar to those caused by the bacteria. |
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Fusarium
stem rot
Pathogen - Fusarium solani or F. oxysporum
Symptoms - Fusarium stem rot appears as a soft, mushy rot at
the base of a cutting or rooted plant. The rotten area frequently
has a purplish or reddish edge. Fusarium spp. sometimes form tiny,
bright red, globular structures (fruiting bodies) at the stem base.
Control - Thiophanate methyl compounds (Domain, Cleary's 3336,
Systec, Fungo, Topsin M) are labeled and should control Fusarium stem
rot. Treat cuttings with a dip or a post-sticking drench to control
losses. Remove infected plants from stock areas as soon as they are
detected. Since Fusarium stem rot appears similar to Erwinia blight,
accurate disease diagnosis is very important prior to applications
of pesticides. |
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Myrothecium
leaf spot
Pathogen - Myrothecium roridum
Symptoms - Leaf spots are generally found at wounds, although
it is common to find no obvious wound and very large (up to 1 inch)
leaf spots. The spots are usually tan to brown and may have a bright
yellow border. Black and white fruiting bodies of the pathogen form
in concentric rings on the leaf underside.
Control - Keep plant leaves as dry as possible and avoid excessive
handling. Although both chlorothalonil (Daconil 2787) and mancozeb
(Manzate 200 80WP) provide good control, they are not labeled on aglaonema
for this disease. |
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Anthracnose
Pathogen - Colletotrichum spp.
Symptoms - Leaf spots are initially tan and water-soaked and
may have a bright yellow halo. Fruiting bodies of Collectotrichum
spp. appear in concentric rings of tiny black specks on the upper
surface.
Control - Keep foliage dry, and protect from cold water drips
due to condensation on overhead structures. Many fungicides, such
as mancozeb (Manzate 200DF), iprodione (Chipco 26019 50WP) or thiophanate
methyl compounds (see Fusarium listing above) are effective but may
not be labeled for aglaonema. |
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Dasheen
mosaic
Pathogen - Dasheen mosaic virus (DMV)
Symptoms - Dasheen mosaic virus is rarely seen on aglaonema
but symptoms can include mosaic, leaf distortion and stunting.
Control - DMV can be spread by both aphids but more commonly.
It is very important to use pathogen-free stock since the symptoms
of DMV are not always noticeable. No chemicals have any known effects
on this virus disease. |
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