Common diseases and disorders of Coleus

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


Pathogen - Botrytis cinerea
Symptons- Botrytis leaf and blossom blight usually appear on lower leaves of cuttings in contact with the potting medium. The water-soaked spot may enlarge rapidly to encompass a large portion of the leaf blade or even the entire cutting. The area dies and turns dark brown to black with age. When night temperatures are cool, day temperatures warm, and moisture conditions high, the pathogen readily sporulates on both leaves and flowers, covering them with grayish-green dusty masses of conidia.
Control- Controlling Botrytis blight of foliage plants is particularly important during the winter months. Methods which improve foliage drying and reduce moisture condensation on foliage during the nights reduce the need for fungicide application. These include fans to circulate the air and facilitate rapid leaf drying, and heating and venting at sunset to reduce the amount of moisture in the greenhouse air. On some crops, Botrytis spores are more likely to become airborne and spread when the plants are handled. It may be advisable to time fungicide applications directly following a time when the plants are handled (such as during moving or trimming). Chlorothalonil (Exotherm Termil), iprodione (Chipco 26019), and vinclozolin (Ornalin) are labeled for Botrytis control on coleus.

Pathogen - Genetic variability in the plant
Symptons - Leaves develop yellow variegation that can be mistaken for virus infections. Plants with these symptoms are usually rare unlike those infected with a virus. Distortion can also occur. The reddish-purple coloration on some leaves is not normal for this coleus cultivar.
Control - If the number of off-type plants is high, a new source of plants should be found. Discard those that are found, but don't miss the opportunity for developing a new selection of the plant. This is one of the oldest ways for new plants to come into the commercial trade.


Pathogen - Corynespora cassiicola
Symptons - Leaf spots appear first as tiny sunken areas which are slightly brown. These areas enlarge to about 1/2 inch in diameter and darken with age. Leaf drop is common under optimal conditions for disease expression. Similar symptoms are seen on other plants such as Aeschynanthus, Columnea, Ficus, Nematanthus, Salvia, and Saintpaulia.
Control - Use standard cultural controls for fungal leaf spot disease. Minimize overhead watering or exposure to rainfall which can splash spores to new plants and aid in the germination process. Never use plants with spots for propagation since this makes pathogen spread to the new crop very likely. Iprodione (Chipco 26019) is labeled and should aid in disease control.

Pathogen - Pseudomonas cichorii
Symptons - Spots are water-soaked and turn dark green to black. They may have a yellow edge but this is not common on coleus.
Control - Avoid overhead watering as much as possible to reduce conditions for infection and spread of the pathogen. Preventive applications of a copper bactericide may reduce disease slightly but none are labeled on coleus at this time. Many other hosts of P. cichorii have been identified; chrysanthemum, ferns, ficus, geranium, gerber daisy, and philodendron among others.

Pathogen - Meloidogyne spp.
Symptons - Galls occur on roots and the root system may be drastically reduced; plant stunting and wilting occur when severe infestations are present. This problem is more likely to occur in the landscape than during production.
Control - It is a good idea to examine the roots of all plants for knots and galls before purchasing. Use sterile soil and grow plants off the ground if possible. Check nematicide labels for this plant and application methods.


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