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PLANT PATHOLOGY
| ENTOMOLOGY |
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Project:
Investigation on the fungal diseases of orchids
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T.
K. Bag
Survey
and collection of disease samples from Darjeeling, Mirik and
Sukio pokhari of Darjeeling District (W.B.) and Pakyong of East
Sikkim was done. From the disease samples, fungi were isolated,
purified and identified as follows: |
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| Sl
No |
Orchid
host |
Disease
caused |
Fungus
identified |
| 1 |
Cattleya
sp |
Black
rot |
Pythium |
| 2 |
Cattleya
sp |
Black
rot |
Pythium
andColletotrichum |
| 3 |
Bulbophyllum
sp |
Leaf
spot |
Colletotrichum |
| 4 |
Phiaus
maculatus |
Leaf
rust |
Uredo |
| 5 |
Cymbidium
Sp |
Flower
spot |
Botrytis |
| 6 |
lone
scariosa |
Black
leaf spot |
Colletotrichum |
| 7 |
Zeuxine
sp |
Stem
anthracnose |
Colletotrichum |
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Studies
on the Occurrence of Rust of Phaius
maculates.
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Symptoms
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Prominent
yellow spots with numerous spores, usually on the lower surface and
later on upper leaf surface.
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Pustule
size- 0.5 X 1.0 cm to 1.5 X 1.6 cm.
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Symptoms
rarely found on older leaves, leaf petioles, pseudobulbs, flower
stalks and flowers.
Etiology
The
rust fungus identified as Uredo sp :
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Produce
only urediospores, measure- 25-30 X 14-19 mm.
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Urediospores
small, thin walled, echinulate, ovate to spherical and orange coloured.
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Did
not produce telia and teliospores,
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Spores
remained in mass at the border of the pastules.
Host
range
Among
5 Phaius species viz. Phaius maculata, P. wallichi. P. rnishmensis, P.
tankervilliae and P. densiflora, only P. maculatus were recorded to be
infected with Uredo rust.
Epidemiology
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The
fungus (Uredo sp.) prefers shady place with mild to moderate
temperature.
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Produce
profuse small pastules and urediospores during February to April.
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Preferable
RH range from 30-73% and temperature range
from 13-24.7 0 C.
Occurrence
of orchid wilt (Sclerotium rolfsii) on important Orchids
On
orchids some destructive sclerotial diseases were noticed. Isolation and
purification of the organism confirmed the disease as orchid wilt. The disease was first found to infect pseudobulbs of Coelogyne
corymbosa causing pseudobulb rot and death of entire plant in the
community pot in the month of June 2001. The fungus was found later to
infect several other orchid hosts also.
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Investigation
on the fungal diseases of orchids
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Survey
and collection of disease samples from Darjeeling and Sikkim was done,
fungi were isolated, purified and identified.
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| SL
No |
Orchid
host |
Disease
caused |
Fungus
identified |
| 1 |
Cattleya
sp |
Black
rot |
Pythium |
| 2 |
Cattleya
sp |
Black
rot |
Pythium
and Colletotrichum |
| 3 |
Bulbophyllum
sp |
Leaf
spot |
Colletotrichum |
| 4 |
Phiaus
maculatus |
Leaf
rust |
Uredo |
| 5 |
Cymbidium
Sp |
Flower
spot |
Botrytis |
| 6 |
lone
scariosa |
Black
leaf spot |
Colletotrichum |
| 7 |
Zeuxine
sp |
Stem
anthracnose |
Colletotrichum |
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Studies
on the orchid hosts of anthracnose pathogen Colletotrichum gloeosporioides)
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Colletotrichum
gloeosporioides has
been isolated, purified and identified on many orchid hosts at National
Research Centre for Orchids, Pakyong as follows:
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- Coelogyne
barbata,
- Liparis
plantaginea,
- Paphiopedilum
venustum,
- Cymbidium
devonianum,
- Bulbophyllum
sp,
- Catteleya
sp,
- Zeuxine
sp,
- Otochilus sp,
- Calanthe sp
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.ENTOMOLOGY
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Pest
management in orchids and Bulbous flowering plants
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Survey
on Pests of orchids and their management in Sikkim
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Occurrence
of pests on orchids
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Name
of orchid
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Pests
observed
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Cymbidium
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Mites
(Tetranychus utricae)
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Scales
(Diaspis boisduvali)
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Moth
(Hellula undalis )
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Mealy
bugs (Pseudococcus maritimus)
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Nematode
(Aphelenchoides ritzemaboci)
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Cattleya
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Mealy
bugs (Pseudococcus maritimus)
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Slug
(Deroceras laeve),
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Scales
(Diaspis boisduvali)
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Mites
(Tetranychus utricae)
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Grass
hoppers (Hieroglyphus banian),
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Snail
(Achatina fullica)
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Phalaenopsis
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Slugs
(Deroceras laeve)
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Scales
(Diaspis boisduvali)
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Other
orchid species
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Scales
(Diaspis boisduvali)
Moth
(Hellula undalis) |
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Damage
due to serious pests
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Name
of pest
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Season/
Month
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Plant
portion affected
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Nature
of damage
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Losses
(%) |
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Mites
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April-
May
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Leaves
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Unsightly
leaves due to sucking sap
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-
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Feb-Oct
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Leaves
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Unsightly
leaves due to sucking sap
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Dry
season
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Leaves
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-
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2.5
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Scales
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Rainy
season
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Leaves
and young shoots
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Unsightly
leaves due to sucking sap
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Mealy
bugs
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Rainy
season
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Leaf
sheath
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Unsightly
leaves due to sucking sap
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Slugs
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Whole
year
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Root
tips
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Root
tip eaten
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3.0
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Night
summer
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Leaves
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5.0
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Mites
feeding results in unsightly leaves, their presence was noticed during
February to October.
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Scales
were serious during rainy season attacked on young shoots.
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Slugs
were nocturnal, cut the root tips and leaves.
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Mealy
bugs were more prevalent in rainy season; suck the cell sap from leaf
sheath.
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Control
Measures used against serious pests
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Name
of pest
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Control
measures/ pesticides
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Criteria
for pesticide use
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%
Spray
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Interval
of spray
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Satisfaction
Yes/
No |
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Mites
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Kelthane
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2.0
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Weekly
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Yes
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Kelthane
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2.0
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As
and when occur
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Yes
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Kelthane
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2.5
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Yes
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Scales
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Phosphamidon
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0.2
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Monthly
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Yes
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Mealy
bugs
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Phosphamidon
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-
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As
and when occur
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Yes
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Slugs
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Slugit
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Calendar
based
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2.5-4
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15-20
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No
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Physically
removed
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When
seen
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No
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Mites
could easily be managed with kelthane 2.0- 2.5 %.
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Phosphamidon
0.2 % on monthly interval control scales as well as mealy bugs.
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Growers
were not satisfied with slugit 2.5- 4% .as well as mechanically
removal of slugs.
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Conclusions
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The
pests associated with orchids in Sikkim are not so serious and cause
negligible damage (<5%).
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The
pests observed could easily be managed with existing control methods.
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The
damage due to pests is very less may be due to tough physique of
orchids accompanied with adverse climatic conditions like severe cold.
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The
growers of Sikkim could get rid off pest problem with cleanliness and
enough ventilation besides existing control measures
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