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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
