Cabbage White Butterfly
Description
CWB are a large, day flying moth with yellow-white coloured wings spanning about 45 mm. Forewings are black – tipped and females have two characteristic black spots on the forewing, while males have only one. Eggs are pointed, approximately 2.5 mm long, and initially white in colour, which darken to yellow as they mature. Eggs are laid singly onto leaves and usually hatch within four days. Larvae are green, with light-coloured hairs and a pale-yellow stripe down their back, reaching a length of 30 mm when fully grown. For pupation to take place, mature larvae weave a silk thread cocoon which is attached to the underside of older leaves or to stems. Pupae are greyish brown, yellow or green and about 18 mm long. Under favourable conditions, the life cycle of CWB generally takes about four weeks.
The larvae of CWB feed ravenously on the leaves of brassica crops, chewing large holes in the leaves. In severe infestations, the whole leaf can be eaten, as well as the growing tips and shoots. It is generally unlikely floral parts will be attacked if leaf material is available, however larvae can be found in floral parts, deeming the heads unmarketable.
Control
Combining biological, cultural, and chemical practices is the best practice to effectively control CWB and preventing significant economic losses. Several natural predators such as spiders, ladybird beetles and lacewings along with parasitoid species can help control CWB. Minimising the use of broad-spectrum insecticides is vital to encourage and preserve these natural predator populations.
Ensure old crops are destroyed or ploughed in to minimise breeding and feeding sites for CWB. Where subsequent crops are planted, a physical barrier between crops is recommended to reduce pest pressure. If possible, consider planting crops when pest pressure is low to avoid heavy infestations and therefore crop losses.
Control is vital during seedling and hearting growth stages and most effective on the small caterpillar stage. Consequently, vigilant monitoring is important so growers can act quickly and spray when grubs are small. Good spray coverage is important, as CWB can easily hide in the leaves of cabbages and heads of cauliflower. To enable better spray coverage crops can be planted in wider rows.
Once threshold levels are reached, a timely application with an insecticide may be required. Larvin® has excellent residual activity and is fast acting, it is registered for the control of CWB in brassica crops. Larvin can be highly disruptive to beneficial insects, so consultation with your agronomist or consultant is recommended before use. Belt® is soft on beneficial insects whilst still providing good residual control. Belt is registered for the control of CWB in brassica vegetables, brassica leafy vegetables, herbs and root and tuber vegetables.
References
Climate Watch (cited 2020), ‘Cabbage white butterfly’, Climate Watch an Initiative of Earthwatch Institute, Cabbage White Butterfly - ClimateWatch Australia- Citizen Science AppDepartment of Primary Industries and Regional Development (DPIRD), (2017), ‘Diagnosing cabbage white butterfly’, DPIRD, Diagnosing cabbage white butterfly | Agriculture and Food
Dimsey, R, Carey, D and Henderson, S (2010), ‘Brassica Best Practice Integrated Pest Management’, Department of Primary Industries, Ausveg page 16, TL197.pdf (ausveg.com.au)
GlobalNet Academy (cited 2021), ‘Identifying Cabbage White Butterfly’, GlobalNet Academy Controlling Cabbage White Butterflies in Tasmanian vegetable gardens – Know your enemy! | GlobalNet Academy
Learmonth, S and Lancaster, R (2020), ‘Insect pests of vegetable brassicas in Western Australia’, Department of Primary Industries and Regional Development (DPIRD Insect pests of vegetable brassicas in Western Australia | Agriculture and Food
