References
Common diseases and disorders of Anthurium

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

 

Anthracnose
Pathogen - Colletotrichum gloeosporioides
Symptoms - Tiny brownish spots on the flower spadix develop during high humidity. These spots enlarge, appear water-soaked and brown to black. Sometimes the entire spadix will turn black as spots merge. The shape of most spots is angular due to the shape of the spadix tissue. As the disease becomes more severe, masses of orangeish spores form on dead areas. Leaves and spathes are rarely if ever infected.
Control - One fungicide which aids in control of this disease is mancozeb (Dithane M-45). In Hawaii, anthurium breeding programs for cut flower production routinely select for resistance to this disease. Resistance levels of the potted hybrid anthuriums have not been determined.

Chimaera
Pathogen - Genetic variability in the plant
Symptoms - 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, especially on some cultivars produced in tissue-culture where the plant genetics may become skewed due to the unusual growing conditions.
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.

Copper toxicity
Pathogen - Copper from foliar applications of bactericides or nutrients
Symptoms - New leaves deveop pocking and small yellow spots. Distortion and burning at edges can occur.
Control - Not all anthurium cultivars are sensitive to copper. Many of A. andraeanum used for cut flowers have proven too sensitive for applications from copper containing bactericides. Test each new cultivar in a small plot before starting broadscale use of copper containing products.

Phytophthora leaf spot, flower blight, and root rot
Pathogen - Phytophthora parasitica
Symptoms - Phytophthora leaf spot and flower blight are characterized by small water-soaked spots on leaves and/or spathe tissues. Spots turn black and remain wet appearing as they enlarge. They can encompass the entire flower or leaf under conditions of both high temperature and moisture which are favorable to pathogen development. When conditions become drier or cooler spots dry and can appear papery but usually remain quite dark in color.
Phytophthora root rot shows the same symptoms as many other root rot diseases. Leaves wilt, may turn yellow or pale green and eventually die. Plants are frequently stunted and examination of roots reveals their rotted condition. Initial infections of the roots appear as small water-soaked grayish or brown areas. These spots can rapidly expand to affect the entire root system. Severely infected plants may have no living roots remaining by the time they are examined.
Control - Prevention is always the best control of a soil-borne pathogen like Phytophthora. Use clean pots, potting media, and grow plants on raised benches. Since anthuriums are rarely tolerant of heavy or poorly draining potting media, the appropriate mix is critical. Even regular fungicide applications to infected plants in a heavy potting medium will not control this disease on some potted anthuriums. Fungicides which are registered for anthuriums which should aid in control of this root rot include metalaxyl (Subdue) and etridiazol (Terrazole and Truban). Although these fungicides should be effective none are registered for use as a foliar spray and control of leaf or flower blight. Mancozeb (Dithane M-45) is registered as a foliar spray on anthuriums and may give some control of flower or leaf blight.

Xanthomonas blight
Pathogen - Xanthomonas campestris pv. dieffenbachiae
Symptoms - Symptoms usually start on the leaf margins where the bacterium enters through hydathodes. Spots are first translucent, yellowish and water-soaked. They may take a long time to enlarge but eventually they can encompass the entire leaf margin, invade the center of the leaf and even cause leaf drop. Mature spots are black and usually surrounded by a bright yellow halo. If the anthurium becomes systemically infected, the plant will show signs of yellowing, stunting and loss of lower leaves. Eventually systemically infected plants die.
Control - Use of bactericides for control of even the foliar phase of Xanthomonas blight is rarely effective. Anthurium andraeanum cultivars typically show phytotoxic responses to both streptomycin sulfate and copper compounds although these products can be used safely on some of the potted anthurium hybrids. Avoidance of this disease is the most effective control. Scout the crop routinely and frequently to detect early symptoms of Xanthomonas blight. Some growers report effective control by removing symptomatic leaves, although this method has obvious drawbacks for potted foliage producers. Limit overhead irrigation to reduce pathogen spread and keep in mind that most of the commonly produced aroids (dieffenbachia, aglaonema and syngonium) are also hosts of this pathogen.

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