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Cercospora
leaf spot
Pathogen - Cercospora sp.
Symptoms - Cercospora leaf spot is typified by tan to black
raised areas found on leaf undersides. The areas appear similar
to a condition called edema and are swollen and irregularly shaped.
It is very difficult to isolate the causal organism from these spots
and frequently the two conditions are confused. P. obtusifolia cultivars
are especially susceptible to Cercospora leaf spot.
Control - Thiophanate methyl (Cleary 3336 or Domain) is labeled
for use on peperomias and can control this leaf spot disease. Be
sure to spray the undersides of the leaves where the spores are
located. |
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Phyllosticta
leaf spot
Pathogen - Phyllosticta sp.
Symptoms - Phyllosticta leaf spot occurs primarily on the
watermelon peperomia. Leaf spots are dark brown to black and dryish
and have concentric rings of light and dark tissue. Spots commonly
start on leaf margins and can spread across the entire leaf.
Control - Remove and destroy infected leaves. Keep the plant
foliage dry and treat with thiophanate methyl (Cleary 3336 or Domain)
or mancozeb (Dithane T & O) according to labeled directions. |
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Rhizoctonia
leaf spot
Pathogen - Rhizoctonia sp.
Symptoms - Peperomia obtusifolia cultivars are susceptible
to Rhizoctonia sp. which causes a mushy, dark-brown to black leaf
spot. Spots are elliptical to irregularly shaped and concentric
rings of raised and depressed tissue form in these areas. Under
warm conditions, the web-like mycelium of the pathogen can be seen
covering the affected plants.
Control - Remove and destroy severely infected plants or
areas in the stock bed. Treat the bed with thiophanate methyl (Cleary
3336 or Domain) being sure to thoroughly saturate the potting medium
as well as cover the tops of the plants since this pathogen is soil-borne. |
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Myrothecium
leaf spot
Pathogen - Myrothecium roridum
Symptoms -Myrothecium leaf spot most frequently appears on
wounded areas of leaves such as tips and breaks in the main vein
which occur during handling. The leaf spots are watery and nearly
always contain the black and white fungal fruiting bodies in concentric
rings near the outer edge of the spot. They are seen on the leaf
undersides. The presence of these bodies is good evidence that the
cause is Myrothecium.
Control - Iprodione (Chipco 26019 50WP) and mancozeb (Dithane
T & O) provide good control of this disease on other foliage
plants. Avoid wounding leaves and keep the foliage as dry as possible.
Many other plants are hosts of M. roridum such as Aglaonema, Aphelandra,
Begonia, Calathea, Dieffenbachia, Spathiphyllum and Syngonium and
these plants must be included in control programs. |
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Phytophthora
and Pythium stem and root rot
Pathogens - Phytophthora parasitica or Pythium splendens
and many other species
Symptoms - Plants rot at the soil line and show a mushy black
lesion which can extend upwards into the leaves of the plants. Roots
of infected plants are blackened and mushy and their outer cortex
can be easily removed from the inner core.
Control - Always use new pots and potting medium and grow
plants on raised benches to avoid infestation from the native soil.
Metalaxyl (Subdue formulations) and several formulations of etridiazol
(Terrazole and Truban formulations) are effective in controlling
these diseases and are labeled for peperomias. |
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Sclerotium
stem rot (also called Southern Blight)
Pathogen - Sclerotium rolfsii
Symptoms - Stem rot caused by this pathogen is characterized
by a brown mushy area at the soil line of the cutting. Plants which
are in the rotting phase as well as established plants are frequently
lost to this disease. The brown fruiting bodies of the pathogen
are commonly found in the rotted area. These structures are tan
to dark brown and are round and the size of mustard seeds. Masses
of white cottony mycelial growth are also found.
Control - Cuttings should be inspected carefully for symptoms
of this disease and discarded if they are infected. Always use new
potting medium and pots and watch plants carefully for the symptoms
of stem rot. Although pentachloronitrobenzene (PCNB-Terraclor) is
not labeled for use on peperomias, it is the only effective chemical
control for southern blight. |
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Ring
spot
Pathogen - Peperomia ring spot virus
Symptoms - Infected plants show a variety of symptoms including
ring spots (rings of light or dark pigmentation), leaf distortion
and stunting for the green variety of P. obtusifolia. The virus
appears as necrotic lesions (brown areas) on the variegated cultivars
and infected leaves generally fall off the plant.
Control - Collect and destroy all peperomias with these symptoms
since no chemicals can control a virus disease. Be careful not to
transmit the virus by using contaminated cutting tools - clean in
between plants if this virus disease is suspected. |
