Cabbage webworm

Pests of Field Crops in Southern Africa

CABBAGE WEBWORM

(Lepidoptera: Pyralidae)

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Text Box: Another minor pest of brassicas is the cabbage webworm, Hellula undalis. This pest is found mainly in the hearts of the plants, associated with webbing but possibly more than that of greater cabbage moth. The caterpillars grow to between 12 and 16 mm in length, and are coloured a dull creamy-pink with five longitudinal darker stripes along the body. They often tie the leaves together with the webbing, which becomes soiled with frass and dirt. The moths are smaller than greater cabbage moths, with grey-brown forewings, whitish hindwings and wingspan of about 17 mm. TOP

Text Box: The main plants attacked are cabbages, cauliflowers, radishes and some of the cruciferous flowering plants such as stocks (Matthiola sp.). TOP

Text Box: Webworm seems to be a problem of young plants. The caterpillars tend to feed exclusively under the covering of the webbing, in a relatively small area, so that they are not immediately noticeable. They excavate holes in the stem and can destroy the growing points so that surviving plants tend to produce suckers and no decent head. TOP

Text Box: Eggs are laid singly in crevices mainly between the base of petioles and stem, and hatch in 3-4 days in the summer. They soon begin to produce the webbing under which they feed, and within three to four weeks become fully-grown. They then spin an irregular cocoon covered with soil particles or frass, and these are placed either on the plants or in the soil at their bases. Development can be at any time of the year, and is obviously much slower in the winter months. TOP

Text Box: This is a sporadic pest, but once it has gained hold within the webbing and near the centre of the plant it is very difficult to control. Control measures should therefore be based on scouting for its presence, and should preferably be applied while the plants are still small. There are no specific pesticide registrations but contact chemicals as applied for diamond-backed moth should be effective. TOP

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Cabbage webworm. (Photo: M. Shepard, G R Carner, P A C Ooi, Bugwood.org.)