- Sunflower

Sunflower Sunflower

Blight of Sunflower


Alternaria helianthi

In a Nutshell

  • Affects all above-ground parts of the plant.
  • Appearance of dark brown spots in various shapes.
  • Stunted growth.
  • Reduction in stem girth and head diameter.
  • Severe reduction in seed yield.
 - Sunflower

Sunflower Sunflower


Brown spots may be found on leaves, petioles, stem, sepals, and petals of the host plant. The fungus causes seedling blight and head rot disease. On the leaves, the lesions are dark-brown with a paler margin and a yellow halo. At the disease progresses, the size gets increased to about 2-3 cm diameter and eventually coalesce to produce an irregularly shaped lesion, causing blighting and withering of leaves. These will be surrounded by chlorotic zone with the grey-white necrotic center. Spots first appear on the lower leaves and subsequently spreads to middle and upper leaves. On the stems, lesions occur as circular, elongated or striated black spots. On the sepals and petals, the spots are similar to those on the leaves but are smaller (0.5-2 cm diameter) and coalesce. The consequences of infection are blight and defoliation, destruction of the flowers and seed-heads, wilting, cracking of the stem and ultimately death of the plant. Sometimes rotting of flower heads also occurs.

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It is caused by fungus Alternaria helianthi. The pathogen survives on seeds and plant residues. The plants are susceptible to infection from the emergence stage to harvesting. The disease extensively spreads under warm, dry weather conditions with periodic rain. Excessive application of nitrogen fertilizers intensifies plant damage.

Organic Control

To enhance the self-cleaning capacity of soils after harvesting the precursor in autumn, it is recommended to apply biological products based on Trichoderma spp. or biological control agents of phytopathogens (Bacillus spp., Pseudomonas spp.).

Chemical Control

Always consider an integrated approach with preventive measures and biological treatments, if available. For planting, use seeds treated with fungicides containing thiram, fludioxonil, iprodione (contact fungicides), imazalil, tebuconazole, and flutriafol (systemic fungicides). During the vegetation period, use of formulations containing famoxadon (contact fungicide), cymoxanil (locally systemic fungicide), boscalid, propiconazole, and tebuconazole (systemic fungicide) can control the disease.

Preventive Measures

  • Plan crop rotation of 3-4 years.
  • Apply lime in acidic soils.
  • Plough deep with a single-furrow plough to ensure good drainage of soil and removal of plant debris.
  • Inter-row tillage eliminates soil crust and improves soil aeration.
  • Ensure balanced nutrient levels with phosphorus and potassium fertilizers.
  • Cropping during late season can decrease the disease incidence.
  • Use available disease-resistant varieties.

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