Common diseases and disorders of Gloxinia

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


Air pollution
Pathogen - Sulfur dioxide in the air
Symptoms - High sulfur dioxide pollution causes marginal burning and shredding of the interveinal areas. These symptoms can mimic worm damage.
Control - Protect gloxinia from exposure to air pollution if possible or grow crops with lower sensitivity to sulfur dioxide.

Botrytis blight
Pathogen- Botrytis cinerea
Symptoms - Spots usually appear on flowers or leaf edges or at wound sites, especially on petioles near the pot rim or in contact with the potting medium. A small, water-soaked spot can rapidly enlarge and cover the entire leaf. Sporulation on necrotic leaves or flowers appears as a powdery grayish-green mass.
Control - Watch for Botrytis when the following conditions occur - low light, high humidity, poor air circulation and warm days with cool nights. Fungicides such as vinclozolin (Ornalin 50WP) and iprodione (Chipco 26019 50WP) effectively control Botrytis blight on many ornamentals.

Fertilizer induced chlorosis
Pathogen - Excess or inadequate fertilization
Symptoms - Plants may be stunted and fail to grow properly as well as becoming light green or even yellow. The older leaves are frequently the first to show deficiency due to inadequate nitrogen levels.
Control - Always use the recommended rates of fertilizer. It is sometimes impossible to determine whether too much or too little fertilizer has been applied based on symptoms alone. Soluble salts of the potting medium should be checked to verify the source of the problem. If this is not possible, then it is sometimes helpful to look at the root systems of affected plants. In general, plants that have received too much fertilizer will have poorly developed root systems while those without sufficient fertilizer will have over developed roots compared to the top growth. Be careful to look at the root quality if few roots have developed since root rotting fungi (Pythium or Rhizoctonia) can also be responsible for root loss.

Myrothecium crown rot
Pathogen - Myrothecium roridum
Symptoms - Myrothecium crown rot most frequently appears on as plants reach the flowering stage. The entire plant can collapse due stem rot. Leaf spots can also occur and are watery or mushy. They nearly always contain the black and white fungal fruiting bodies in concentric rings near the outer edge of the spot or rotted areas. The presence of these bodies is good evidence that the cause is Myrothecium. Newly planted materials are especially susceptible to this disease since wounds aid in disease spread and development.
Control - Iprodione (Chipco 26019 50WP) provides some disease control. Preventive treatments to newly rooted cuttings may be required. In addition, mancozeb (Dithane M-45) provides good control of the leaf spot on some plants. Avoid wounding leaves and keep the foliage as dry as possible. Always use a reputable source for gloxinia propagative materials to avoid introducing this disease into your nursery.

Phytophthora stem and root rot
Pathogen - Phytophthora parasitica
Symptoms - Phytophthora stem and root rot appears very similar to Myrothecium crown rot caused by M. roridum. Mixed infections with the two pathogens sometimes occur. Spots can form on leaves or petioles and are watery and collapse rapidly. The plant usually dies. Culture of the pathogen is necessary prior to developing a control program for either disease.
Control - Avoid over watering since water-logged roots are easily attacked by P. parasitica. Use pathogen-free pots, potting media and plant material. A wide variety of fungicides are registered and effective for control of Phytophthora stem and root rot. Etridiazol is available in a variety of formulations (Terrazole or Truban) and as a combination product with thiophanate methyl (Banrot 40WP). Two other compounds, metalaxyl (Subdue formulations) and propamocarb (Banol 66.5EC) can be used for Phytophthora diseases. Since the pathogen can be present in the root system and/or potting medium, these fungicides must be applied to the potting medium to achieve disease control. As always, use new potting media and pots to avoid contamination from previous crops.

Rhizopus blight
Pathogen - Rhizopus sp.
Symptoms - A soft, mushy brown rot can start anywhere on infected plants including cutting bases, leaves, flowers and shoot tips. The white mycelium and black sporangia of the pathogen form rapidly on all infected plant parts, giving them a fuzzy or bearded look.
Control - This disease can spread by air movement as well as splashing from rainfall or irrigation practices. It is generally only a problem during the conditions with high temperatures and relative humidities. Keep plant stress as low as feasible to aid in resisting this disease. Extensive and serious cultural controls have proven effective in controlling this disease on some floricultural crops. There are no fungicides labeled for this use although dicloran (Botran) is used in postharvest control of a similar disease on stone fruits.

Tomato Spotted Wilt
Pathogen- Tomato Spotted Wilt Virus
Symptoms - TSWV can infect many flowering and foliage potted plants as well as vegetables such as tomato and lettuce. Symptoms on gloxinia are dramatic with concentric rings of sunken tissue that can be tan or black. This virus is spread by thrips such as Western flower thrips as well as by using infected stock plants.
Control - Thrips control must be the first step in controlling this virus disease. Since the host range of TSWV is so large all plants should be examined before entering the greenhouse. Do not use any plants or parts which come from stock with these symptoms.


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