Crucifer Pests
 

Cabbage Webworm
Hellula undulis

Found worldwide

Damage Symptoms

Silken webbing on the surface of the inner leaves and stalks is evident. The surrounding regions have obvious feeding holes. The area beneath the webbing contains frass and other insect remains. The growing point of seedlings may be severely defoliated. If the plant survives, several small heads may form.

Insect Characteristics

Chewing mouthparts. Cabbage webworm (CWW) Caterpillars are dusty yellow with broad purple stripes along the length of their bodies. Adult moths are rather nondescript and gray with small brown spots or specks.

Where to Look

Inspect the young growing points, inner leaves and stalks for chewing damage. If webbing is found, look underneath it for the webworm. Positive identification can only be made if the insect is found, but if webbing with dirty frass underneath is found, it is likely the damage is caused by this species.


Technical information

Female moths lay eggs on foliage near young growing points. After hatching, larvae bore in to the growing point and cover themselves with a silken web, which has an exit hole in it. Larvae are voracious feeders. They pupate on fallen leaves and other debris on the ground.


Control

Since CWW attacks on the growing point this pest is not serious in important head-forming crops like cabbage and Chinese cabbage after head formation. Thus only seedlings, up to 4 weeks after transplanting, need protection.

Chemical insecticides are effective and there are no indications that CWW has developed resistance to any chemical. Soil application of granules of mephosfolan, terbufos, carbofuran or fensulfathion at the time of transplanting as well as sprays of chlorpyrifos, EPN, triazophos, methidathion, methomyl and parathion give good control of the pest. Application of any of these WP or EP formulation products once every 2 weeks after first application within 3 days after transplanting is effective. Newer insecticides permethrin, abamectin, teflubenzuron, chlorfuazuron, triflumoron, cyhalothrin are also effective. Malaysian farmers have found that treating only the shoot, rather than the entire plant, can protect the crop. This "point application" will spare parasitoids and predators that might visit the plant and help control CWW and other pests.

The use of natural enemies is not widely practiced. Strategies using resistant cultivars or sex pheromone traps have yet to be developed.