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
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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.
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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.
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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.
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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. |
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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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