References
Common diseases and disorders of Aphelandra (Zebra Plant)

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.
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Corynespora leaf spot
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.

Crinkle leaf
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.

Chlorosis
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 fertilized adequately.

Kutilakesa canker
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.

Myrothecium leaf spot
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 85F but can be a problem throughout the year in Florida. Temperatures above 90F greatly inhibit Myrothecium and make chemical application less important.

Phytophthora stem rot
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.

Tomato spotted wilt
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.

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