The article throws light upon the five major diseases found in marigold. The diseases are: 1. Damping off 2. Leaf Spots and Blight 3. Inflorescence Blight 4. Flower Bud Rot 5. Powdery Mildew.
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.