Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most destructive diseases affecting rice crops worldwide, and India is no exception. This disease can cause substantial yield losses, posing a significant threat to food security in a country where rice is a staple food.
What is Rice Blast and How Does it Occur?
Rice blast can infect all above-ground parts of the rice plant, including leaves, stems, nodes, and panicles. Symptoms initially appear as white to gray-green lesions with brown borders. These lesions expand into spindle-shaped spots with ashy centers. In severe infections, multiple spots can merge to form large, irregular patches, leading to extensive damage.
The fungus overwinters in infected crop debris and seeds. Under favorable conditions like high humidity and warm temperatures, it produces spores that can spread by wind to initiate infections in new crops.
Losses Due to Rice Blast
Rice blast can cause substantial yield losses, ranging from minor to total crop failure in extreme cases. The severity of the disease depends on various factors like the rice variety's susceptibility, weather conditions, and crop management practices.
Why Do Farmers Struggle to Control Rice Blast?
- Rapid Evolution of the Pathogen: Magnaporthe oryzae is notorious for rapidly evolving and overcoming the resistance in rice varieties. This makes relying on single-gene resistance in rice problematic and contributes to breakdowns in control.
- Over-reliance on Single Active Ingredient Fungicides: Continuous use of fungicides with a single mode of action can quickly lead to the fungus developing resistance, rendering the products ineffective.
- Inadequate Disease Monitoring and Timing: Effective management of rice blast requires early detection and timely fungicide applications. Farmers may lack resources or knowledge to identify disease symptoms early enough. Additionally, fungicide applications need to be made before or at the very early stages of infection for the best control.
- Environmental Factors: Weather conditions like prolonged rainfall and high humidity can significantly favor the development of rice blast, increasing the challenges for effective control.
Why Single Active Ingredient Fungicides are Unsuitable
The issue with single active ingredient fungicides is the higher risk of developing fungicide resistance in the pathogen. When a fungus is repeatedly exposed to a single mode of action, it can develop mutations that make it less sensitive to or even completely resistant to that fungicide. To prevent resistance, best practices emphasize the use of fungicides with multiple modes of action.
Strategies for Effective Rice Blast Control
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Integrated Pest Management: A combination of strategies is crucial to manage rice blast effectively. This includes cultural practices (crop rotation, sanitation), the use of resistant rice varieties, and the judicious use of fungicides with multiple active ingredients.
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Fungicides with Broad-Spectrum Activity: Your provided list highlights various fungicides with multiple active ingredients from different chemical classes. Their combined action offers broader-spectrum disease control, reducing the risk of resistance development. Let's discuss some of the key active ingredients:
- Tricyclazole: Interferes with melanin biosynthesis, a vital process for fungal infection in the rice plant.
- Tebuconazole, Hexaconazole, Difenoconazole, Propiconazole, Prochloraz: These "azole" fungicides disrupt the synthesis of ergosterol, a vital component of fungal cell membranes.
- Azoxystrobin, Picoxystrobin, Kresoxim-methyl: Belong to the "strobilurin" class, inhibiting fungal respiration.
- Carbendazim: A benzimidazole fungicide, disrupts fungal cell division.
- Mancozeb, Zineb: Broad-spectrum protectant fungicides affecting multiple metabolic pathways within the fungus.
- Kasugamycin: An antibiotic, disrupts protein synthesis in the pathogen.
The Importance of Fungicide Rotation and a Holistic Approach
Effective control of rice blast requires a planned approach that includes fungicide rotation with different modes of action, timely applications, and a combination of strategies that promote plant health and resilience.
Combo fungicides for rice blast control
- Sedaxane 12.61% w/w + Azoxystrobin 3.15% w/w + Thiamethoxam 22.06% w/w (Vibrance Integral, Syngenta India Seed treatment)
- Carbendazim 1.92% + Mancozeb 10.08% GR (SAAFILIZER GR, UPL India) (with basal dose)
- Tricyclazole 18.0% w/w +Tebuconazole 14.4% w/w SC (Tiktok, TimTom)
- Tricyclazole 45% + Hexaconazole 10% WG (GreenMax, Monitor)
- Tricyclazole 20.4% w/w + Azoxystrobin 6.8% w/w SC (Nova Trioxy)
- Tebuconazole 15% + Zineb 57% WDG (UPL TEZING )
- Tebuconazole 50% + Trifloxystrobin 25% WG (Bayer Nativo)
- Propiconazole 10.7% w/w + Tricyclazole 34.2% w/w SE ()
- Propiconazole 13.9% + Difenoconazole 13.9% EC (Prodizole)
- Prochloraz23.5% + Tricyclazole 20.0% w/w SE
- Picoxystrobin 6.78% + Tricyclazole 20.33 %w/w SC
- Kresoxim-methyl 40% + Hexaconazole 8% WG
- Kasugamycin 6 % + Thifluzamide 26% SC w/v
- Kasugamycin 5% + copper oxychloride 45% WP
- Iprodione25%+ Carbendazim25%WP
- Hexaconazole 4% + Zineb 68% WP
- Hexaconazole 5.00% + Validamycin 2.50% SC
- Hexaconazole 4% + Carbendazim 16% SC
- Flubendiamide 7.5% + Kresoxim-Methyl 37.5% SC
- Difenoconazole 6% + validamycin 6% SC
- Difenoconazole 10 % + Mancozeb 50% WDG
- Carbendazim 25%+ Mancozeb 50% WS
- Carbendazim12%+ Mancozeb63%WP
- Azoxystrobin 16.7% + Tricyclazole 33.30% SC
- Azoxystrobin 5.1%w/w +Tebuconazole 9.1% w/w+ Prochloraz 18.2 % w/w EC
- Azoxystrobin 120 g/L + Tebuconazole 240 g/L SC
- Azoxystrobin 10% + Fipronil 5% SC
- Azoxystrobin 18.2% + Difenoconazole 11.4% w/w SC
