Common diseases and disorders of Peperomia

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


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.

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.

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.

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.

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.

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.

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.


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