Sunflower; LEAF SPOT; RUST

Sunflower: Helianthus annuus L. Family: Asteraceae 1. LEAF SPOT The disease is commonly found on all varieties of sunflower in the winter season. Symptoms: The pathogen produces brown coloured spots on the leaves, stem, sepals and petals. The lesions on the leaves are dark brown with pale yellow margins and yellow halo, at first the spot is small and become larger as the disease advanced with irregularly circular shape (up to 2-3 cm in diameter).  Causal Organism: The fungal pathogen causing leaf spot of sunflower is Alternaria helianthi Hansf. The mycelium is septate, branched and bearing conidiophores. The conidiophores are cylindrical, pale grey-yellow, straight or curved, geniculate, simple or branched, 2-5 septate and measuring 31-80 x 8-11 µm. The conidia are cylindrical to long ellipsoid, straight or slightly curved, pale yellow to pale brown, 1-11 transversely septate, occasionally longitudinal septa, constricted at the septa, rounded at both ends and measuring 42 – 110 x 15 – 28 µm. The conidia are produced singly on the conidiophores. The fungal pathogen grows well and produced abundant conidia on culture media. Disease Cycle: The disease is appearing each year through soil borne fungal inoculums. The pathogen is survived in plant debris. Disease Management: The disease can be effectively controlled by spraying of Mancozeb (0.3%) thrice with 7-10 days intervals, Dithane M-45 (0.2%) or Thiovit or any other copper fungicide with ten days intervals.     2. RUST The rust disease of sunflower is common, widespread and most severe. The severe infection of disease reduces yield considerably. Symptoms: The small reddish brown spots covered with rusty coloured dust are appear on the lower leaves and then spread to all leaves even to other green parts of the head. The leaves turn yellow but only sometimes fall down from the plants. The pycnia and aecia stages usually occur on volunteer seedling plants which are growing among the debris of the previous crop. The inoculum from the affected crop is spread by wind to the healthy cultivated crop. Causal Organism: The fungal pathogen of sunflower rust is Puccinia helianthi Schw. which is an autoecious pathogen and produces uredia and telia on the leaves. The uredosori are dark cinnamon brown and uredospores are round elliptical or ovoid, wall dark cinnamon brown, finely echinulate with two equatorial pores and measuring 17 – 21 x 24 – 27 µm. The teleutospores are two celled, elliptical or oblong, 21 – 31 x 28 – 50 µm, obtuse or rounded at the tip and base, constricted at the septum, chestnut brown, smooth and colourless pedicel which is longer than spore. Disease Management: The sanitation practices like crop rotation, destruction of volunteer seedlings and trash of previous year crop may be helpful in checking the disease. The spraying of fungicides such as Thiovit, Dithane M-45 or Nickle chloride is effectively control the disease. The cultivation of resistant sunflower varieties like MSFH-1, MSFH-6, MSFH-8, MSFH-9, BSF-1 and VSF 182 is the best way to control the disease completely.