COMMON WHEAT (GOM) DISEASES IN BANGLADESH Farmer's Guide: Symptoms, Prevention & Control ==================================================== 1. WHEAT BLAST (Gomer Blast Rog) ==================================================== Causal organism: Fungus (Magnaporthe oryzae Triticum pathotype) SYMPTOMS - Wheat spike (head) turns white at the point of infection, spreading quickly in warm, humid weather - Blackish-grey spots appear where the spike is infected; upper part turns white - If infection starts at the base of the spike, the whole spike dries and turns white - Grains become shriveled, discolored, and unfit for use - On leaves: small, water-soaked, eye-shaped grey spots - Most damaging around heading to flowering stage HOW IT SPREADS - Spreads through infected seed - Favored by 12-24 hours of leaf/spike wetness plus temperatures of 18-25°C - Survives on grassy weeds between seasons PREVENTION & CONTROL - Use certified, disease-free seed - Grow blast-tolerant varieties (BARI Gom 28, 30, 32) or resistant variety (BARI Gom 33) - Sow between November 15-30 to avoid rain/high heat during heading - Treat seed before sowing with Provax 200 WP or Vitavax 200 FF (3 g or 3 ml per kg seed) - Keep fields and bunds weed-free - Spray fungicide (Nativo 75 WG or Amistar Top 325 SC) once at heading and again 12-15 days later - Wear gloves and a mask when spraying ==================================================== 2. LEAF SPOT / SPOT BLOTCH (Pata Dhosa Rog) ==================================================== Causal organism: Bipolaris sorokiniana (fungus) SYMPTOMS - Small, elongated to oval, brown to blackish spots scattered on leaves - As spots mature, centers turn light brown/tan with a dark brown margin - Large, well-developed spots produce heavy spore growth and can cover most of the leaf - Severely affected leaves dry up completely (blighted) - Infection on stem and nodes can cause the plant to lodge (fall over) - Ear/spikelets can also be infected under favorable conditions; grains become discolored, shriveled PREVENTION & CONTROL - Use disease-free, certified seed; treat seed with fungicide before sowing - Practice crop rotation with non-cereal crops - Avoid excess nitrogen; ensure balanced fertilization - Remove and destroy infected crop debris after harvest - Spray a recommended fungicide (e.g., Tebuconazole or Propiconazole based) if disease appears early, especially in humid weather - Grow tolerant varieties where available ==================================================== 3. STEM RUST / BLACK RUST (Kando Marchha Rog) ==================================================== Causal organism: Puccinia graminis f. sp. tritici (fungus) SYMPTOMS - Appears later in crop growth, usually after heading - Elongated, reddish-brown (rust-colored) pustules erupt on stem, leaf sheath, and leaves - Pustules burst, releasing powdery brown spores that spread to reinfect the crop - As the plant matures, pustules turn dark brown to black (hence "black rust") - Torn, tattered appearance of leaf/stem tissue where pustules erupt - Can cause significant yield loss if infection starts early and weather stays warm and humid HOW IT SPREADS - Spores are carried long distances by wind - Favored by warm daytime temperatures (25-30°C), wet weather, and prolonged dew - Needs living plant tissue to survive; volunteer wheat/barley plants after harvest can carry it over PREVENTION & CONTROL - Grow rust-resistant wheat varieties - Sow early (within recommended window) to avoid infection during grain-filling - Destroy volunteer wheat/barley plants after harvest - Monitor fields regularly after heading, especially in warm, humid weather - Apply a recommended fungicide preventatively if rust is forecasted or first pustules are seen, targeting the flag leaf stage - Avoid excess nitrogen fertilizer, which promotes lush, susceptible growth ==================================================== 4. POWDERY MILDEW (Gura Sada Rog) ==================================================== Causal organism: Blumeria (Erysiphe) graminis f. sp. tritici (fungus) SYMPTOMS - Small yellow spots appear on leaves 5-7 days after infection - White, fluffy/powdery fungal growth develops on these spots (leaves, stem, sometimes head) - Infected leaves yellow and die early - Later, small black specks (fungal fruiting bodies) appear on old infected tissue near plant base - Most common in lush, early-sown, nitrogen-rich crops during tillering stage - Usually does not persist much beyond ear emergence PREVENTION & CONTROL - Avoid highly susceptible varieties; choose tolerant ones - Use recommended seed rate (about 100 kg/ha) — avoid overly thick/lush stands - Avoid excess nitrogen; apply potassium fertilizer as recommended instead - Remove volunteer wheat plants and crop debris from the field after harvest - Maintain regular, balanced irrigation (avoid excess moisture and humidity buildup) - Apply a sulfur-based or triazole fungicide if infection is severe early in the season ==================================================== GENERAL TIPS FOR ALL WHEAT DISEASES ==================================================== - Always start with healthy, certified seed and treat seed before sowing - Follow recommended sowing time and seed rate for your area - Avoid excess nitrogen fertilizer; balance with phosphorus and potassium - Keep fields and field bunds free of weeds and volunteer plants - Rotate crops where possible instead of continuous wheat - Scout fields regularly, especially during humid or rainy weather - When spraying fungicide, always wear gloves and a mask, and follow label instructions - Contact your nearest agricultural extension office or BARI Wheat Research Centre for the latest recommended varieties and chemicals