Disease - Agricultural Research and Extension Unit

Common diseases affecting selected ornamental crops and
their management
by
Dr (Mrs) Arty Gungoosingh- Bunwaree
RS/SRS
Plant Pathology Division
INTRODUCTION
•
According to Digest of Agricultural Statistics 2010,
i.
Cut flowers and foliage (2010):
Exported for about Rs 85.5 M
Imported for about Rs 12.3 M
ii.
About 261 people employed in the sector
ISLANDWIDE SURVEY
Islandwide survey over 2 years
to identify major diseases
across selected ornamentals
nurseries
•
Ornamentals commonly grown on commercial
basis: rose, gerbera, chrysanthemum, orchids,
anthurium, foliage plants, pine, bromeliads.
ISLANDWIDE SURVEY ON ORNAMENTAL DISEASES
No. of site visits conducted
115
No. of localities visited
25
Site
Open field (OF) / Protected
(P) cultivation
Ornamental Crops grown
1. Reduit
P and OF
Rose, gerbera, chrysanthemum, orchids,
anthurium, bromeliads
2. Richelieu
P and OF
Rose, gerbera, chrysanthemum, bromeliads,
heliconia
3. Wooton
P and OF
Rose, gerbera, chrysanthemum, anthurium,
alpinia, heliconia
4.
Quatre Bornes
P and OF
Foliage plants, pines, chrysanthemum, orchid,
potted plants
5.
Camp Fouquereaux
P
Rose, gerbera
6.
Highlands
P
Rose, gerbera, orchids
7.
Mare Chicose
P
Rose
8.
Moka
P
Rose, gerbera, chrysanthemum
9.
Beau Bassin
P and OF
Foliage plants, pines, potted plants , orchids
OF
Rose
10. Petit Bel Air
Islandwide survey continued
11. Fond Du Sac
P
Foliage plants, pines, potted plants
12. Cluny
P
Rose, gerbera, chrysanthemum, anthurium
13. St Hubert
P
Rose, gerbera
14. Union Park
P
Rose, gerbera
15. D`Epinay
P
Rose, gerbera
16. Le Val
P
Rose, gerbera
17. Montagne Longue
P
Orchids
18. Medine
OF
Pines, potted plants , palms
19. Queen Victoria
P
Rose, gerbera, chrysanthemum, anthurium
20. Morc St Andre
P
Foliage plants, pines, potted plants
21. Arsenal
P and OF
Foliage plants, pines, potted plants
22. Trianon
P and OF
Rose, gerbera, chrysanthemum, orchids, bromeliads,
foliage plants, pines, potted plants
23. Terracine
P and OF
Foliage plants, pines, potted plants , palms
24. Riviere des Anguilles
P
Foliage plants, pines, potted plants , palms
25. Petit Raffray
OF
Foliage plants, pines, potted plants , bromeliads
Common diseases and their management on:
ROSE
GERBERA
CHRYSANTHEMUM
ORCHIDS
Crop: Rose
Varieties screened: Black Baccara, Shakira, Altesse, Red Baccara, Lovely Red, Taubie Kaushik, Memoire H,
Copper Tone, Rina Hurgo, Just Joey, Leana D, Johanesburg Sun, Blue Moon
Disease: Powdery mildew
Symptoms: Stems and flower parts covered
with white fungal growth.
Disease incidence: 60%
Disease severity: 30%
Conditions that favour disease development
•
High humidity
•
Warm temperatures
•
Poor sanitation at field level
Disease development
Fig.1 : Evolution of powdery mildew in 4 shadehouses
YEAR 1
YEAR 2
Locality of
shadehouses:
Réduit, Wooton,
Queen Victoria, Quatre
Bornes
Disease management
1. Sanitation; prune affected leaves and flowers, collect and destroy all crop debris
2. Ensure proper air circulation in shadehouse
3. Chemical treatment with Folicur/ Score 250 EC
4. use correct dosage & alternate chemical products
Crop: Rose
Disease: Black spots
Symptoms: Brown to black round spots with feathery
edges form on leaves. Leaves yellow and fall. Small,
purplish spots form on canes.
Disease incidence: 20%
Disease severity: 20%
Disease management:
1. Sanitation to remove infected canes and leaves.
2. Water in a manner that keeps foliage surfaces dry.
3. Chemical treatment to protect new leaves; Bravo 720 SC, Mancozeb 80WP.
Crop: Rose
Disease: Downy mildew
Symptoms: Brown spots form on leaves. Leaves yellow
and fall. Small spots may form on canes and may kill
twigs.
Disease incidence: 15%
Disease severity: 20%
Disease management:
1. Sanitation
2. Water in a manner that keeps foliage surfaces dry.
3.
Chemical treatment with Aliette 80 WP, Ridomil Gold MZ 68
Crop: Rose
Disease: Rose canker
Symptoms: Reddish-brown spots on canes
turn light to dark brown. Cankers girdle and
kill the cane.
Disease incidence: 12%
Disease severity: 40%
Disease management:
1. Select healthy planting material.
2. Removed infected canes making an inclined cut immediately above a bud.
3. Apply Copper paste after pruning.
4. Disinfect tools regularly.
Crop: Rose
Disease: Botrytis flower blight
Symptoms: Small water-soaked lesions form on petals.
Gray fungal growth covers infected petals.
Disease incidence: 8%
Disease severity: 75%
Disease management:
1. Remove and destroy infected and fallen flowers & leaves.
2. Water in a manner that keeps foliage surfaces dry.
3. Chemical treatment with Bravo 720 SC, Rovral FLO.
Survey Findings
Crop: Gerbera
Varieties screened: Jaska, Double Dutch, Zembla, Picobello, Parado, Cacharelle, Candella, Gladiator,
Opus, Marimo, Robun Daryl, Endura, Pink Power, Winter Queen, Pentura.
Disease: Powdery mildew
Symptoms: Stems and flower parts covered with white fungal
growth.
Disease incidence: 55%
Disease severity: 35%
Disease management
1. Sanitation; eliminate affected leaves and flowers, collect
and destroy all crop debris
2.
Ensure proper air circulation in shadehouse
3. Chemical treatment with Folicur/ Score 250 EC; use
correct dosage & alternate chemical products
Disease: Leaf spots (Alternaria, Anthracnose)
Symptoms: Brown specks on florets and the leaves, or
circular leaf spots that coalesce with one another during
moist weather resulting in rolling and drying of leaves .
Disease incidence: 40%
Disease severity: 40%
Disease management:
1. Excessive watering and crowding of plants should be avoided.
2. Diseased leaves should be collected and eliminated.
3. Chemical treatment with Score 250 SC.
Crop: Gerbera
Disease: Botrytis flower blight
Symptoms: Petioles have long brown spots. Leaves yellow
and die. Petals have tan spots. Stems at soil level are killed.
Infected tissues become covered with gray fungal growth.
Disease incidence: 6%
Disease severity: 75%
Disease management:
1. Ensure good air circulation.
2. Maintain low humidity.
3. Avoid watering late in the day.
4. Remove crop debris.
5. Chemical treatment with Bravo 720 SC, Rovral FLO.
Crop: Gerbera
Disease: Crown and Root rot
(Fusarium, Pythium or Rhizoctonia)
Symptoms: Stunted growth. Plants wilt
and die.
Disease incidence: <5%
Disease severity: 80%
Disease management
1. Sanitation, i.e discard infected plants.
2. Use sterilised potting media.
3. Chemical treatment with Ridomil Gold MZ 68.
Crop: Chrysanthemum
Varieties screened: Ilona, Fleury Dark, Pink Splendide, Dark Ruth
Disease: Leaf spots caused by
Colletotrichum, Alternaria or Stemphylium or
Septoria
Symptoms: Brown or pin-point dead spots develop
on leaves or petals. If enough spots are present, an
entire flower may die.
Disease incidence: 50%
Disease severity: 20%
Disease Management:
1. Sanitation
2. Avoid overhead irrigation.
3. Chemical treatment Score 250 EC, Mancozeb 80 WP.
Crop: Chrysanthemum
Disease: Botrytis flower blight
Symptoms: Light brown spots form on lower petals.
Browning spreads to other petals. Infected tissues become
covered with dusty gray spores.
Disease incidence: 20%
Disease severity: 80%
Disease management:
1. Sanitation
2. Avoid overhead irrigation.
3. Chemical treatment with Bravo 720 SC, Rovral FLO.
Crop: Chrysanthemum
Disease: Pythium stem and root rot
Symptoms: Stems turn dark brown to black at the soil line.
Plants are stunted, wilt, and die.
Disease incidence: <5%
Disease severity: 80%
Disease management:
1. Plant in pasteurized soil or soilless mix free of the pathogen.
2. Carry out soil drench with Ridomil Gold MZ 68.
Crop: Orchids
Varieties screened: Dendrobium, Vanda, Cymbidium, Phalaenopsis
Disease: Leaf Spots - Cercospora, Phyllosticta and Septoria
Symptoms: Tiny spots on leaf surface develop into yellow
lesions or enlarge to become dark brown to black, circular
or irregular lesions.
Spots may merge to form large,
irregular patches on the leaf. Heavily infected leaves fall
prematurely.
Disease incidence: 50%
Disease severity: 60%
Disease management:
1. Remove infected leaves .
2. Reduce leaf wetness
3. Chemical treatment with Score 250 EC, Mancozeb 80 WP.
Crop: Orchid
Disease: Anthracnose (leaf and flower spots)
Symptoms: Leaf tips turn brown beginning at the
apex and proceeding toward the base. Dark brown
patches develop, as concentric rings across the leaf.
Flowers develop watery, black or brown spots that
can merge to cover the entire flower.
Disease incidence: 20%
Disease severity: 40%
Disease management:
1. Sanitation
2. Good air circulation
3. Chemical treatment with Score 250 EC, Bravo 720 SC.
Crop: Orchid
Disease: Black Rot - Pythium and Phytophthora
Symptoms: Brown spots on leaves spread to roots. Wilting of
plants
Disease incidence: 8%
Disease severity: 75%
Disease management:
1. Isolate infected plant
2. Carry root drench with Ridomil Gold MZ 68.
Crop: Orchid
Disease: Fusarium wilt
Symptoms: Fusarium blocks the flow of moisture
through the plant’s vascular system, such that
yellow, thin, wilted leaves eventually die. Pinkish-
purple discoloration on the outer layers of the
rhizome.
Disease incidence: 6%
Disease severity: 40%
Disease management:
1. Discard infected part of rhizome
2. Sterilise tools after cuts.
3. Chemical treatment with Rovral Flo.
Crop: Orchid
Disease: Virus diseases (Cymbidium mosaic virus,
Odontoglossum ringspot virus)
Symptoms: Light and dark green patches on leaves,
yellowing or dying of leaves or portions of leaves,
malformation of the leaves, flowers, stunting of plants,
break in flower colour
Disease incidence: <5%
Disease severity: 20%
Disease management
1. Careful selection of planting material
2. Disinfect tools regularly
3. Proper sanitation
4. Rogue out infected plants
Evaluation of fungicides for management of powdery mildew
Product
Active Ingredient/
Chemical group
Rate
Effectiveness
1.
2.
3.
4.
5.
6.
- Triazole
- Triazole
- Mancozeb
- Bicarbonate
- Strobirulin
- Pyraclostrobin (Strobilurin)
and Boscalid (Carboxanilide)
- 0.5 mL/L water
- 1mL/L water
- 4.0g/L water
- 4.0 g/L water
- 0.3g/L water
- 0.6g/L water
High
High
Medium
Low
Medium
High
7. Collis
-
- 0.8mL/L water
High
8. Funginil Powder
- Botanical fungicide (herbal
extracts)
- 2g/L water
??
Score
Folicur
M45
Potassium Bicarbonate
Stroby
Bellis
Kresoxim-methyl + Boscalid
Important points to consider for optimum disease management in ornamentals
1. Use healthy planting material
2. Observe proper sanitation
3. Disinfect tools regularly
4. Carry out chemical treatment only when necessary
5. Remember to use proper dosage and alternate fungicides
Acknowledgements
•
PRS, Lab Manager and colleagues of
Plant Pathology Division, AREU
•
Crop Extension Staff of AREU
•
Mrs H.Gowreesunker and Mr M.Nathoo (Research Scientists/SRS)
•
Ms M Dookhan, Biometrician, AREU
•
Ornamental growers who participated in the survey
For further information, contact the
Plant Pathology Division of AREU at
Réduit or your nearest Crop
Extension Office

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