The document summarizes several diseases that affect marigold plants and their control methods. It describes diseases such as damping off caused by Rhizoctonia solani, leaf spots and blight caused by Alternaria, Cercospora and Septoria species, inflorescence blight caused by Alternaria zinnae, flower bud rot caused by Alternaria dianthi, and powdery mildew caused by Oidium sp. and Leveillula taurica. It provides details on symptoms, causal organisms, and recommendations for control which include soil drenching, fungicide spraying, and dusting with sulfur powder.

1. Wilt and Stem Rot (Phytophthora cryptogea): The fungus affects the collar portions of
the plants. In nursery the infection results in damping-off and is aggravated by soil
moisture. In the field the infected plants show wilting. French marigold and dwarf
varieties are less susceptible whereas the African types are highly susceptible to the
disease.
Control: The disease may be controlled by soil treatment with Captan, Mancozeb,
Metalaxyl and Fosetyl-Al.
Collar Rot (Phytophthora sp.; Pythium sp.): The symptoms are in the form of black
lesions developed on the main stem. Rotting at the collar regions causes death of the
plant. Soil sterilization and controlled watering help in reducing the disease incidence.
Leaf Spot and Blight (Alternaria, Cercospora and Septoria sp.): Brown necrotic spots
develop on leaves, which get enlarged at the later stage of infection. The entire
foliage gets damaged and results in poor vegetative growth.
Control: The disease may be controlled by Spraying of fungicides is helpful in
controlling the disease.
Powdery Mildew (Oidium sp.; Leveillula taurica): The symptoms are in the form of
whitish powdery growth on the aerial parts of the plant.
Control: Spraying Sulfex (3g/litre of water) can effectively control the disease.
Flower Bud Rot (Alternaria dianthi): The fungus infects the young flower buds. The
infected buds shrivel and become dark brown in colour. The pathogen also infects
leaves causing blight. The infection is visible in the form of brown necrotic spots on
margins and tips of older leaves.
Control: Spraying of Mancozeb (2g/litre of water) effectively controls the flower bud
and leaf infections.
Damping Off (Pythium sp.): The disease is most prevalent at the seedling stage.
Necrotic spots and rings develop on the young seedlings causing collapse of the
seedlings. Considerable loss is sustained if seedlings are not properly looked after.
Control: Soil sterilization by Formalin @ 2% before sowing and spraying of Dithane
Z-78 @ 2g/ litre of water are effective in controlling the disease.
Marigold Diseases & its Control

2. Marigold (Tagetes spp.)-Botrytis Blight
.Cause Botrytis cinerea, a fungus that colonizes dead, dying, and wounded plant parts. From these infections it can
attack healthy tissues. A moist, humid environment is ideal for pathogen sporulation and spread. Conidia may come
from sources in and outside the greenhouse. It is found everywhere plants are grown and has a wide host range.
Flower petals are most susceptible at any stage of development.
Symptoms Flower petals become water soaked and brown and may show the gray sporulation of the fungus.
The gray fuzz characteristic of this disease consists of spores of the fungus.
Flower parts become necrotic and die. A gray mass of spores develops on necrotic tissue during wet conditions.
Cultural control
•Remove all dead and dying plant parts (particularly blossoms) on and around plants.
•Avoid overhead irrigation or apply such that plants are not wet for extended periods of time.
•Space plants for good air circulation.
Chemical control Best used with cultural controls. Tank-mix and/or alternate products with different modes of action to prevent
the buildup of resistant fungi. Limit the use of any one group during crop production.
•Astun at 10 to 17 fl oz/100 gal water. Group 7 fungicide. 12-hr reentry.
•Broadform at 4 to 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
•Chipco 26019 N/G at 1 to 2.5 lb/100 gal water. Group 2 fungicide. 12-hr reentry.
•Copper-Count-N at 1 quart/100 gal water. Oregon only. Group M1 fungicide. 48-hr reentry general or 24-hr reentry for greenhouse.
•Decree 50 WDG at 0.75 to 1.5 lb/100 gal water. Group 17 fungicide. 12-hr reentry.
•Emblem at 2 to 4 fl oz/100 gal water. Use with oils or adjuvants may cause plant damage. Group 12 fungicide. 12-hr reentry.
•Exotherm Termil at 1 can/1500 sq ft of greenhouse. It ignites to form a vapor that condenses back on the plants. See label for details.
Group M5 fungicide. 24-hr reentry with no ventilation or 12-hr reentry with ventilation.
•Fore 80 WP at 1.5 lb/100 gal water. Do not use on French dwarf-double or signet-type marigold seedlings. 24-hr reentry.
•Medallion WDG at 2 to 4 oz/100 gal water. Using with oils or adjuvants may damage plant. Group 12 fungicide. 12-hr reentry.
•Mozart TR at 1 can/4,500 sq ft of greenhouse. Group 12 fungicide. 12-hr reentry with no ventilation.
•OHP 6672 4.5 F at 10 to 14.5 fl oz/100 gal water plus another fungicide. 12-hr reentry.
•Orkestra at 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
•Pageant at 12 to 18 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
•Palladium at 4 to 6 oz/100 gal water. Avoid excessive runoff to small plants, which may result in stunting and/or chlorosis. Group 9 +
12 fungicide. 12-hr reentry.
•Phyton 27 at 1.3 to 2 oz/10 gal water. Group M1 fungicide. 48-hr reentry.
•Spirato GHN at 2 to 4 fl oz/100 gal water. Use with oils or adjuvants may cause plant damage. Group 12 fungicide. 12-hr reentry.
•Switch WG at 11 to 14 oz/A. Do not use within 7 days of harvest. Group 9 + 12 fungicide. 12-hr reentry.
•Terraguard SC at 4 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Biological control
•Prestop (Gliocladium catenulatum strain J1446) at 3.5 oz/5 gal water. Do not use with other products in the tank. 0-
hr reentry.

3. 5 major diseases of marigold
• Disease # 1. Damping off:
• It is caused by Rhizoctonia solani and appears as brown necrotic spots, girdling the radicle which later
on extends to plumule and causes pre-emergence mortality. Post-emergence symptoms appear on lower
part of hypocotyl as water soaked, brown, necrotic ring, leading to collapse of seeding.
• When infected seedlings are pulled, the root system appears partially or fully decayed. To control the
disease soil drenching with Brassicol (0.3%) should be followed. Proper drainage should be provided
in the nursery bed.
• Diseases # 2. Leaf Spots and Blight:
• Various species of Alternaria, Cercospora and Septoria are known to cause leaf spot or blight of
marigold. Alternaria tagetica and A. tenuissima damage the foliage of the plants. The symptoms appear
as minute brown circular spots on lower leaves and enlarge at later stage of infection leading to
premature defoliation and ultimate death of the plants. To keep the disease under check the marigold
crop should be sprayed with Dithane M-45 fungicide @ 0.2% at fortnightly intervals starting from the
first appearance of disease symptoms.
• Diseases # 3. Inflorescence Blight:
• This disease is caused by Alternaria zinnae. Elongated lesions are formed on inflorescence. Symptoms
may appear as large irregular blotches on the leaves also which is light tan to dark brown with
zonation’s. This can be effectively controlled by spraying the crop with Dithane M-45 (0.2%).
• Diseases # 4. Flower Bud Rot:
• It is caused by Alternaria dianthi. The disease appears mainly on young flower buds and results into
their dry rotting with brown scorched, necrotic discoloration of sepals and stalk. The ray and disc
florets also turn brown.
• At later stages buds become shriveled, turn deep brown and dry up. Symptoms are less prominent on
mature buds but these buds fail to open. On older leaves few deep brown necrotic spots develop. To
control this disease regular spraying of the crop with Dithane M-45 fungicide @ 0.2% should be
followed.
• Diseases # 5. Powdery Mildew:
• Oidium sp. and Leueillula taurica have been reported to cause powdery mildew of marigold. The
whitish, tiny superficial spots appear on leaves which later on result in the coverage of whole aerial
parts of plant with whitish powder. The disease can be controlled by following spraying with
Karathane (40 E.G.) @ 0.5% or dusting with sulphur powder a fortnightly intervals.