is a Plant Pathologist and President of Chase Research Gardens, Inc.
C.R.G. is a private research and consulting corporation specializing in
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 - Corynespora cassiicola
Symptoms - Leaf spots start on leaf edges, tips and sometimes
centers near pot edges, the potting medium and at wound sites. They
are dark brown to black and often appear wet. This disease can be
a serious problem on cuttings rooted under mist and on bottom leaves
of potted plants. Spots start on lower leaves, especially those
in contact with the potting medium or those which are wounded. Lesions
expand rapidly and are black and may reach 5 cm or more when conditions
are favorable. There is rarely any halo surrounding lesions on these
hosts. In addition, the white 'Apollo' zebra plant was more susceptible
than the dark-green `Dania' zebra plant. Lesions appeared on wounded
zebra plants about 7-14 days after inoculation. Corynespora leaf
spot of zebra plant is usually only a problem during the propagation
phase since only then are plants kept under very high moisture and
humidity conditions. Apparently healthy cuttings may develop severe
symptoms of disease.
Control - Elimination of overhead water can control this
disease. In situations in which chemicals are needed, both mancozeb
compounds (Mancozeb 200 or Dithane M-45) and chlorothalonil (Daconil
2787) provide excellent control.
Pathogen - unknown
Symptoms - Leaves crinkled, size reduced, internodes shortened
with axillary bud proliferation. Aphelandra leaf crinkle has been
recognized in Florida since 1973 and was described from Texas in
1981. The disease is typified by pronounced stunting of terminal
growth, reduced leaf size and downward puckering and curling back
of leaves. Symptoms are most severe under high light levels (1500
ft-c. and above) but cannot be reproduced with light alone. Affected
plants continue to produce symptomatic leaves regardless of cultural
condition. In addition, production of rooted cutting from crinkle
affected plants is reduced in both quality of cuttings available
and ability of the cutting to root. The search for a biotic agent
has indicated that this disease is not caused by a fungus, bacterium,
rickettsia-like or mycoplasma-like organism. Treatment of affected
plants with 100-150 ppm of chlortetracycline or tetracycline did
not result in remission of symptoms. Electron microscope examination
of affected and unaffected tissue did not reveal virus particles.
Incidence of leaf crinkle increases as both temperature and light
intensity increase, and control should be based on keeping these
cultural conditions at optimal levels for plant production. Symptomatic
plants should be removed from the stock or production area.
Control - The disorder is most severe under high light and
high temperature. No bacteria, fungi or viruses have been found
associated with this disorder and pesticides have no effect. Plants
do not respond to micronutrients or proper environmental conditions.
Eliminate stock plants with this problem and maintain proper light
levels and temperatures.
Pathogen- Low fertilizer
Symptoms - New leaves are light green or yellowish. Older
leaves may be dark green or yellowish depending upon the specific
element of the fertilizer that is missing. When nitrogen is low,
usually the older leaves are yellow and the new leaves are green.
If new leaves are yellow it is possible that plants are low in all
major fertilizer elements.
Control - Always apply recommended levels of fertilizer.
Check soluble salts of the potting medium regularly to make sure
plants need more fertilizer. Don't just fertilize them if they become
yellowish. Many other factors can cause yellowing including fungal
root rots. Be sure that plants have an appropriate pH level. Low
or high pH can result in nutritional problems even when plants are
Pathogen - Kutilakesa pironii
Symptoms - Galls are oriented longitudinally as well as at
nodes and the cut end of stems. Galls formed on leaf mid veins and
petioles are about 6 mm in diameter. Wounded tissue appears to be
a requirement for infection with Kutilakesa pironii. Symptoms of
the disease appear within 3-6 weeks after infection, with continued
development up to 9 months.
Control - This disease is rarely found on aphelandras and
crotons today. Predacious mycophagous mites (Tyrophagus and Peloribates
spp.) are frequently associated with galled tissue and are perhaps
responsible for spread of conidia to new sites. Contamination of
cutting instruments used during plant propagation also leads to
disease spread. It is especially important to keep knives and clippers
sterilized during plant pruning and cutting removal. You can use
alcohol (70%), bleach (10-20%), or quaternary ammoniums (follow
labels) to sterilize cutting instruments.
Pathogen - Myrothecium roridum
Symptoms - Leaf spots caused by this pathogen appear similar
to those caused by C. cassiicola when viewed from the upper leaf
surface. Leaf undersides generally reveal the presence of the fungal
fruiting bodies which are formed in concentric rings within the
dead spots. These fruiting bodies are irregularly shaped black bodies
with a white fringe and are about the size of a pin head.
Control - The same chemical controls apply to Myrothecium
leaf spot as Corynespora leaf spot. Myrothecium leaf spot is most
severe when temperatures are between 70 and 85°F but can be a problem
throughout the year in Florida. Temperatures above 90°F greatly
inhibit Myrothecium and make chemical application less important.
Pathogen - Phytophthora parasitica
Symptoms - Stem rot usually starts at the soil line and causes
a blistering of the stem surface. The lesions are black and slightly
mushy and can extend from the base of the stem up into the petioles
of lower leaves. Complete collapse of the plant is common.
Control - Control should be based on use of pathogen-free
cuttings, pots and potting media since the pathogen is easily introduced
in any of these ways. Chemicals which provide control of this disease
include metalaxyl (Subdue 2E) and etridiazol (Truban or Terrazole).
Both metalaxyl and fosetyl aluminum (Aliette 80WP) are labeled and
effective for this use.
Pathogen - Tomato spotted wilt virus
Symptoms - Black areas form in the white portions near leaf
veins, especially at leaf bases near the stems.
Control - Control thrips populations carefully since they
are the vectors of the viral pathogen. Always examine new stock
carefully for any signs of disease, insect infestation or other
problems. Many labs can verify a diagnosis of Tomato spotted wilt
virus using laboratory tests. Discard and destroy plants with these
symptoms and never propagate from them even if portions of the are
free of disease.