Tobacco Caterpillar - Onion

Onion

Tobacco Caterpillar

Spodoptera litura


In a Nutshell

  • Extensive feeding damage on leaves.
  • Defoliation.
  • Moths with grayish-brown bodies and patterned forewings.
  • Egg clusters on upper leaf blades.

Symptoms

Feeding damage becomes apparent on the leaves. Larvae are scraping the leaf tissue, creating large, irregular shaped holes. It can result in complete defoliation of the plant. Flower buds and pods are also attacked and show feeding holes. In lighter soils also the roots become damaged. Due to extensive feeding, only petioles and branches are left behind.

Trigger

Symptoms are caused by the larvae of Spodotpera litura. Adult moths have grayish-brown bodies and variegated forewings with white wavy markings on the edges. The hindwings are translucent white with brown lines along the margins and the veins. Females lay hundreds of eggs in clusters on the upper leaf blades, covered with golden brown scales. After hatching, the hairless light-green larvae disperse quickly and start feeding gregariously on leaves. Older larvae are dark green to brown with dark spots on the flanks and somewhat clearer bellies. Two yellow longitudinal bands run along the sides, interrupted by black triangular spots. An orange band runs dorsally between these spots. Larvae feed during the night and take refuge in the soil during the day. Larvae and adults thrive at temperatures between 15°C and 35°C, optimum at 25 °C. Low humidity and higher or lower temperatures reduce fertility and prolong their life cycle.

Biological Control

Bioinsecticides based on Nuclear Polyhedrosis Virus (NPV) or Bacillus thuringiensis can be used on eggs and larvae. Bait solutions based on rice bran, molasses or brown sugar can be distributed on the soil in the evening hours. Plant oil extracts of neem leaves or kernels and extracts of Pongamia glabra seeds are highly effective against Spodoptera litura larvae. For example, azadirachtin 1500 ppm (5 ml/l) or NSKE 5% can be used during the egg stage and prevents the egg from hatching.

Chemical Control

Always consider an integrated approach of preventive measures together with biological treatment if available. Extensive insecticide use can lead to resistance in the pest. To control the young larvae, several types of insecticides could be used, for example, products based on chlorpyrifos, emamectin, flubendiamide, chlorantraniliprole, indoxacarb or bifenthrin. Bait solutions also effectively reduce populations of older larvae.

Preventive Measures

  • Use tolerant varieties if available.
  • Sow early to avoid peaks in insect populations.
  • Irrigate regularly to avoid prolonged mid-season drought.
  • Plant trap crops like sunflower, taro and castor oil plant around and within fields.
  • Plant repellent plants such as Ocimum spp (basilicum).
  • Remove weeds 15-20 days after sowing.
  • Build bird perches in several places in the field.
  • Use light or pheromone traps to attract the moths.
  • Check your fields for signs of the disease such as egg masses, feeding damage or the presence of larvae.
  • Collect and destroy egg masses and larvae from trap plants and host plants.
  • Handle your plants carefully during cultivation and avoid plant damage and injuries.
  • Take care of the hygiene of your tools and equipment.
  • After harvest plow deep to expose the pupae to natural enemies and weather-related factors.

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