Sown across 45 million hectares as India’s primary kharif crop, rice is the food security anchor of eastern, southern, and coastal India.
Rice : 5 Major Threats and Their Control
For guidance only. Does not replace local expert advice. Check region-specific recommendations with your nearest KVK or State Agriculture Department before buying seeds, fertilizers, or pesticides.
1. Blast Disease
(Magnaporthe oryzae)
The Threat:
- Rice blast is the most destructive fungal disease of rice worldwide.
- The pathogen attacks all above-ground parts — leaves, nodes, and panicle neck — with highest damage at seedling and panicle-filling stages.
- On leaves, it forms grey, diamond-shaped lesions with brown margins.
- At the node stage, it can girdle nodes and kill the entire upper part of the plant.
- At the panicle neck (“neck blast”), it cuts nutrient flow, leaving grains empty and hollow even if the plant looks healthy.
- Spreads rapidly under high humidity, long leaf wetness, and cool nights below 24°C.
The Solution:
- Grow recommended blast-resistant varieties.
- Maintain adequate silicon nutrition through silica-rich organic matter or slag application; silicon physically toughens leaf cell walls against fungal penetration and is one of the most cost-effective preventive measures available.
- At the first appearance of leaf lesions or at panicle emergence in blast-prone areas, spray Tricyclazole 75 WP (Systemic Fungicide — Melanin Biosynthesis Inhibitor) @ 0.6 g/litre of water.
- Apply a second spray at full panicle emergence in high-humidity conditions.
2. Brown Planthopper
(Nilaparvata lugens)
The Threat:
- The Brown Planthopper (BPH) forms dense colonies at the base of rice plants and sucks phloem sap directly from the stem, depleting the plant’s carbohydrate reserves faster than they can be replenished.
- The result is “hopperburn” — the plant turns yellow, then brown, appears scorched, and dies in circular patches across the field.
- BPH thrives in humid, shaded environments created by dense planting and excessive nitrogen use, and is most active from the booting to the maturity stage.
- Broad-spectrum insecticide sprays made on a calendar basis destroy natural enemies such as spiders and mirid bugs, which normally regulate BPH populations.
- This leads to explosive outbreaks that are often worse than if no intervention had been made.
The Solution:
- Prevention begins with cultural management — use BPH-resistant varieties ; maintain 30 cm row spacing; reduce nitrogen below excessive levels; and drain fields intermittently to disrupt the pest’s preferred environment.
- Conserve natural enemies at all times, particularly spiders, which are highly effective predators and should never be sacrificed to a prophylactic spray.
- Monitor the base of plant stems weekly, not the top of the canopy.
- Apply a chemical spray only when the population crosses the Economic Threshold Level of 1 hopper per tiller (where no predators are visible) or 2 per tiller (where spiders are present).
- Use Buprofezin 25 SC (Insecticide — Insect Growth Regulator) or Pymetrozine 50 WG (Insecticide — Feeding Blocker, IRAC Group 9B) directed at the base of the plant.
- Avoid or minimize the usage of resurgence inducing insecticides pyrethroids (such as cypermethrin, deltamethrin, lambda-cyhalothrin, etc.) — as they may cause BPH resurgence by eliminating natural enemies.
3. Khaira Disease
(Zinc Deficiency)
The Threat:
- Khaira is the visible expression of zinc deficiency in transplanted rice — rusty-brown spots and bronzing appear on young leaves within 2–3 weeks of transplanting.
- Plant growth slows dramatically, and the crop remains stunted throughout the season with reduced tiller number and poor panicle initiation.
- It is most common in the calcareous (alkaline) and waterlogged soils of eastern India, where zinc is chemically immobilised at high pH and is unavailable to roots even when adequate amounts are present in the soil.
- Severe Khaira can reduce yield by 10–20% and is often mistaken for a disease.
The Solution:
- Apply Zinc Sulphate (ZnSO₄) 21% (Micronutrient Fertiliser) @ 25 kg/ha as a basal dose in nursery and main field before transplanting in zinc-deficient soils.
- For visible symptoms, spray 0.5% ZnSO₄ solution (5 g/litre) on young plants twice at 15-day intervals, ensuring good leaf coverage.
- Maintain soil organic matter with FYM — improves zinc availability over time.
- Conduct soil testing for available zinc every 3 years for accurate, need-based application.
4. Bacterial Leaf Blight
(Xanthomonas oryzae pv. oryzae)
The Threat:
- Bacterial Leaf Blight (BLB) spreads rapidly when strong winds and continuous heavy rain carry bacterial cells through water droplets from lesion to lesion across a field.
- It causes water-soaked, yellow-to-white stripes along leaf margins that progressively dry from the tip downward — a symptom easily confused with drought damage in early stages.
- In seedlings, it can cause complete wilting — the “kresek” symptom — destroying transplanted crops before they establish.
- It is most severe at between 25–34°C with humidity above 70%, and is dramatically worsened by excessive nitrogen application, which produces the lush, dense canopy the bacteria multiply in.
- Yield losses can reach 20–30% in severe cases, with quality losses even in milder infections.
The Solution:
- There is no effective curative spray once BLB is established — focus on prevention and crop management.
- Grow recommended resistant varieties.
- Apply nitrogen in moderate, split doses — do not exceed recommended levels.
- Maintain good field drainage and keep fields clean of weed hosts and rice ratoons that serve as bacterial reservoirs between seasons.
- Allow fallow fields to dry completely before the next crop to reduce soil-borne bacterial populations.
- For nursery protection in high-risk areas, use Streptomycin Sulphate 90% + Tetracycline Hydrochloride 10% SP (Bactericide — Antibiotic combination) as seed treatment or nursery spray, or Copper Oxychloride 50 WP (Bactericide / Contact Fungicide — Inorganic Copper) as a preventive foliar spray applied before symptom onset.
- Kasugamycin 3 SL (Bactericide / Fungicide — Antibiotic, registered for both BLB and blast) is also recommended for dual-purpose management in high-pressure seasons.
5. Deep Flooding / Submergence
The Threat:
- Complete submergence of the rice crop for more than three days — a regular annual event in the flood-prone districts — can destroy a standing crop entirely, particularly at the vulnerable tillering stage.
- The oxygen-deficient (anaerobic) conditions created by deep flooding weaken root systems and sharply reduce the number of productive tillers that will eventually bear grain.
- Flooding creates a warm, stagnant environment in which fungal and bacterial diseases amplify rapidly after flood recession.
- Prolonged water stagnation leaches key nutrients — particularly nitrogen and potassium — from the root zone.
- Submergence stimulates methane production by soil microbes, making this both an agronomic and an environmental concern.
The Solution:
- The most reliable solution is varietal — grow submergence-tolerant varieties with the Sub1 gene (has tolerance to complete submergence for up to 14–20 days), such as Swarna-Sub1, which can survive up to 14 days of complete flooding without major yield loss.
- Other options include FR43B (a traditional Indian rice landrace (cultivar) known for its high level of tolerance to flash floods and complete submergence) and Ciherang-Sub1 (an improved, high-yielding rice variety designed to withstand total submergence for up to two weeks) for specific regions. Use varieties recommended for your region.
- Maintain strong field bunds to control floodwater depth and duration.
- Practice Alternate Wetting and Drying (AWD) — allow fields to dry partially between floods to improve root aeration, nutrient uptake, and reduce methane emission.
- There is no chemical control for submergence damage — only varietal choice and field management are effective.
Additional Reads
Ph.D. in Agricultural Engineering.