- Cabbage

Cabbage Cabbage

Cabbage Webworm

Insect

Hellula undalis


In a Nutshell

  • Webbing and frass on cabbage leaves.
  • Frass accumulates at tunnel entrance along stems.
  • Terminal shoots are destroyed.
  • Small clusters of leaves.
  • Adult moth is greyish-brown with wavy lines.

Symptoms

Seedlings are destroyed by the caterpillars. Young caterpillars mine leaves, bore stems, stalk, leaf and veins. They feed externally on the leaves. Larvae bore into the cabbage head and often penetrate the heart of the plant destroying the terminal bud, thus preventing heading. In older cabbage plants, new shoots are produced and the attacked plants produce several small heads of little commercial value. Caterpillar feeding after heading may cause stunting. They spin a silken tube while feeding. Plants will wilt, and frass is exuded from the affected plant parts. Infested plants frequently have several small clusters of leaves which is caused by damage to the central bud and the development of side shoots.

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Hosts

Trigger

The symptoms are a result of the feeding activities of young caterpillars of Hellula undalis in crops of the Brassica family (cabbage, cauliflower), foremost in the tropics and subtropics. Eggs are oval and are laid singly or in groups, sometimes in chains. The eggs are hatched after about three days, and after five developmental stages, they are mature with greyish-yellow and pinkish longitudinal stripes. Caterpillars are creamy white with light pinkish brown stripes along the body and have a black head. Mature caterpillars have faint stripes. At the final stage, caterpillars are 12-15 mm long, feeding from silken cocoons. Forewings are usually greyish-brown with wavy lines and a black spot. Adult moths are greyish-brown in colour, small and rather delicate. The wingspan is up to 18 mm. After emergence and mating, the females lay up to 150 eggs or more over the next 3 to 10 days. The adult moth is capable of flying long distances.

Organic Control

Introduce parasitic wasps such as braconid, ichneumonid and chalcidoid wasps. Bacillus thurigiensis is recommended and should be applied before larvae are protected by their silken webs, and before they have moved into the center of cabbages. Weekly applications of neem can also be effective.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments, if available. The use of insecticides to protect your plants from this pest is difficult as they are protected either by webbing or them burrowing into the crops. Use Acephate and permethrin at 8-10 day intervals. Carbamates and organo-phosphates controlled the moth when applied at first pest appearance on plants.

Preventive Measures

  • Use clean planting materials and transplant only healthy, vigourous insect-free seedlings.
  • Plant trap crops, such as mustard (Brassica juncea) or Chinese cabbage (Bok Choy) between the rows of your brassica crop.
  • The first row of trap crops should be planted about 15 days before transplanting your crop, while the second row follows 25 days after transplanting.
  • Practice regular monitoring of young plants in the nursery and after transplant.
  • Keep your field free from weeds.
  • Inspect crops for the presence of caterpillars and damage symptoms.
  • Practice field sanitation, uproot and burn cabbage and kale stalks.
  • Crop rotation is important to reduce pest populations.

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