References
Common diseases and disorders of Crotons

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

 

Crown gall
Pathogen - Agrobacterium tumefaciens
Symptoms - Slightly swollen areas on the stems, leaf veins and even roots are initially apparent. These swollen areas enlarge and become corky. Galls may also form on the ends of cuttings or stems where cuttings have been removed. In cases of severe infection, they may enlarge and merge to create a very distorted stem or root mass.
Control - Remove and destroy all plants found infected with the bacterium, then sterilize any cutting tools used on them. Since a fungus is also known to cause galls on croton, an accurate disease diagnosis must be made for crotons with gall symptoms.

Xanthomonas leaf spot
Pathogen - Xanthomonas campestris pv. poinsettiicola
Symptoms - Foliar infections on croton start as tiny pinpoint water-soaked areas which can rapidly enlarge to 1/4 inch or more. They tend to remain confined to the areas between leaf veins and are very wet and dark-brown or black appearing when well developed. On some cultivars the lesions have a bright yellow border. Most lesions also show an irregularly shaped border which is corky and especially visible on leaf undersides. All cultivars tested were shown to be susceptible to this pathogen as well as the related plants crown-of-thorns and poinsettia.
Control - Eliminate all stock plants which have Xanthomonas leaf spot. The disease is very difficult to control unless plants are produced without overhead watering or exposure to rainfall. Bactericides such as copper containing compounds may be somewhat effective if used on a preventative and regular basis.

Anthracnose (Colletotrichum sp. or Glomerella cingulata)
Symptoms - Spots form on all ages of leaves and are initially water-soaked, becoming tan with age. Tiny black fungal fruiting bodies sometimes form in the dead tissue of the spot and may appear in concentric rings.
Control - Avoid wet foliage since this is necessary for infection and spread of spores. This is especially crucial during mist propagation. Mancozeb compounds (such as Manzate 200 80WP) and chlorothalonil (Daconil 2787) are effective in controlling anthracnose on many foliage plants. Manzate 200 80WP is labeled for use on this crop. Do not use iprodione (Chipco 26019 50WP) or vinclozolin (Ornalin 50WP) since they can cause stunting or distortion of new leaves on some types of croton.

Botrytis blight
Pathogen - Botrytis cinerea
Symptoms - Large, tan to brown leaf spots with concentric rings, usually found at leaf edges and tips. Botrytis blight occurs primarily in cool periods of the year especially on cuttings during shipping.
Control - The best fungicides for control of Botrytis blight (Chipco 26019 and Ornalin) can cause phytotoxicity on croton. Check labels fopr safe and effective fungicides for crotons in your state. Cultural controls are the same as those listed for anthracnose disease.

Furasium root and stem rot
Pathogen - Furasium solani and F. oxysporum
Symptoms - Furasium root and stem rot typically appears as a soft, ushy rot at the base of a cutting or rooted plant. The rotten area frequently has a purplish or reddish margin. Furasium solani forms tiny, bright red, globular structures (fruiting bodies) at stem bases on severely infected plants. Roots are mushy, brown and easily desintegrate when handled.
Control -If stem rot or cutting rot is a problem, treatment of the cuttings with a dip or a post-sticking drench of thiophanate methyl (such as Clearys 3336) should diminish losses. Remove infected plants from stock areas as soon as they are detected. Since Furasium root and stem rot appears similar to many other root and stem rots, accurate disease diagnosis is very important prior to choice and application of pesticides.

Stunting
Pathogen - Over-fertilization
Symptoms
In general, plants grow slowly and may have burned leaf tips or margins. This may be especially common when too low a light level is unavailable or temperatures are low and plants cannot use the amount of fertilizer they are given.
Control - Always use the recommended rate of fertilizer for the growing conditions. Trying to push this plant to grow faster only results in poor foliar color and slower growth. If the plant appears to be growing too slowly, be sure to have the soluble salts checked to determine whether they are under or over-fertilized. Check the root systems because poorly formed root systems with burned roots can be an indicator of over-fertilization.

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