Maize
Helicoverpa Caterpillar
Helicoverpa armigera
Insect
In a Nutshell
- Feeding damage on flowers, fruits, pods, bolls & leaves.
- Entrance and exit holes, frass marks.
- Growth of secondary pathogens lead to rotting of tissues and fruits.
Maize
Symptoms
Whitish to brown eggs can be found in clusters around floral structures and young leaves on upper canopy. Feeding damage can be found on any plant tissue but are most likely on flowers and bolls/ears/fruits/pods, depending on the host plant. Young larvae scrape the foliage, growing points or the fruiting structure, causing little damage. Older ones bore into flowers or the young boll/ear/fruit/pod, hollowing it from the inside, damaging seeds and making it unfit for marketing. Frass is visible around the feeding holes. The growth of secondary pathogens on the wounds lead to the rotting of the affected tissues.
Recommendations
Organic Control
Trichogramma wasps (T. chilonis or T. brasiliensis) can be introduced coinciding with flower initiation to attack the eggs. Microplitis, Heteropelma and Netelia wasps parasitize the larvae. Predatory bugs (big-eyed bug, glossy shield bug and spined predatory shield bug), ants, spiders, earwigs, crickets and flies attack the larvae and should thus be promoted. Apply bio-insecticides based on spinosad, nucleopolyhedrovirus (NPV), Metarhizium anisopliae, Beauveria bassiana or Bacillus thuringiensis to control the larvae. Botanical products, such as Neem oil, Neem seed kernel extracts (NSKE 5%), chili or garlic may be applied as foliar sprays at bud initiation stage.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Selective insecticide treatment is the best option to rid the field from the pest without affecting beneficial insects. Monitor for eggs and larvae is crucial as the caterpillars become increasingly resilient to insecticidal treatment. Products based on chlorantraniliprole, chloropyrifos, cypermethrin, alpha- and zeta-cypermethrin, emamectin benzoate, esfenvalerate, flubendiamide, or indoxacarb can be used (usually @ 2.5 ml/l). The first application should be at the flowering stage and followed by sprays at 10-15 days interval. Chemical treatment may not be viable in low-value crops.
What caused it?
The damage is caused by the caterpillar of Helicoverpa armigera, a common pest in a number of crops. H. armigera one of the most destructive pests in agriculture. Moths are light brown, with a wingspan of 3-4 cm. They generally have yellow to orange or brown forewings mottled with darker patterns. Hindwings are whitish, with dark veins and dark elongated spots on the lower edges. Females lay spherical, whitish eggs singly or in clusters on flowers or leaf surfaces, mainly on the top canopy. The larvae are olive green to dark reddish-brown, depending on the maturation stage. Their body is speckled with little black spots and they have a dark head. At later maturity stages, lines and bands develop along their back and flanks. As they reach maturity, they pupate in the soil. The population normally peaks during fruit/pod/boll development, which results in high yield loss.
Preventive Measures
- Use resistant or tolerant varieties if available.
- Plant early to avoid population peaks of the pest.
- Leave sufficient distance between plants.
- Provide uncultivated marginal areas to break the life cycle.
- Place bird perches to attract birds that feed on the caterpillars.
- Use trap crops such as marigold (Tagitus erecta) every 5 or 6 rows.
- Use light or pheromone traps to monitor or mass-catch the moths.
- Avoid water stress by providing good drainage.
- Monitor plants for the presence of eggs and damage to flowers, fruit pods or bolls.
- Hand-pick larvae and leaves or plants with eggs.
- Remove infected plants from fields as well as weeds in and around the field.
- Clear all harvest residues after each cropping cycle.
- Plow deeply after harvesting to expose the pupae for natural predators and solar rays.
- Avoid monocultures and implement intercropping with beneficial plants.
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