Maize Stem Borer
Chilo partellus
📖 Description
Maize Stem Borer (also called Spotted Stem Borer) is the most important pest of maize and sorghum in the Indian subcontinent, causing 25-80% yield loss. Female moths lay eggs in masses on the underside of leaves. Newly hatched larvae feed on leaves for a few days, then bore into the stem, where they feed internally, causing ‘deadheart’ (central shoot dries up) in young plants and chaffy panicles in older plants. Because larvae feed internally, insecticide contact is poor — granular application in leaf whorls before larval entry is essential. Push-pull intercropping with Napier grass (trap crop) and Desmodium (repellent) has been widely adopted across eastern Africa and is gaining traction in India.
⚠️ Symptoms to watch for
- Deadheart (drying of central shoot) at vegetative stage, holes in stems with frass, broken stems, chaffy panicles, 'red leaf' symptom in sorghum, stunted plants, yield loss 25-80%
🩹 Treatment
- Apply carbofuran 3G granules @ 8 kg/ha in leaf whorls 20 days after sowing, install pheromone traps @ 8/ha, release Trichogramma chilonis @ 50,000/ha, apply neem oil 5ml/L, remove and destroy infested plants
🌿 Organic treatments
- Install pheromone traps @ 8/ha, release Trichogramma chilonis @ 50,000/ha weekly, apply Bacillus thuringiensis @ 2 g/L in whorls, apply neem cake @ 250 kg/ha as basal, apply sand + ash mix in whorls, handpick egg masses
🧪 Chemical treatments
- Carbofuran 3G @ 8 kg/ha granules in whorls at 20 DAS, Phorate 10 G @ 10 kg/ha in soil, Chlorantraniliprole 18.5 SC @ 0.3 ml/L spray, Lambda-cyhalothrin 5 EC @ 1 ml/L, Cartap hydrochloride 50 SP @ 2 g/L in whorls
🛡️ Prevention
- Plant early, use resistant varieties (CO 1, CO 2), intercrop with legumes (pigeon pea, cowpea), practice crop rotation, remove and destroy infested plants, deep plough after harvest, plant push-pull strategy (Napier grass, Desmodium), conserve predatory bugs and parasitic wasps, balanced fertilizer use
🪴 Affected plants
- Maize, Sorghum, Pearl Millet, Sugarcane, Finger Millet, Rice (sometimes), Wild Grasses
🦋 Natural predators
- Trichogramma chilonis, Cotesia flavipes, Spiders, Predatory Bugs, Birds, Earwigs
🌱 Host plants
- Zea mays, Sorghum bicolor, Pennisetum glaucum, Saccharum officinarum, Eleusine coracana
🔄 Lifecycle
- Female lays 200-500 eggs in 1-3 masses on the underside of leaves.
- Eggs hatch in 4-7 days.
- Larvae feed for 25-40 days, passing through 5-6 instars.
- Pupation occurs inside the stem, lasting 7-14 days.
- Adults live 4-7 days.
- Total life cycle 35-55 days; 4-6 generations per year.
📅 Season
- Active Jun-Oct during Kharif, peak at 20-40 days after sowing
🔎 Appearance
- Adults are small straw-yellowish moths with dark spots on forewings.
- Larvae are pinkish-white with a brown head and four longitudinal dark stripes, growing up to 25 mm.
- They bore inside maize stems.
💥 Damage level
- High
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- Indian Subcontinent
- East Africa
- Southeast Asia
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