Controlling Cabbage White Butterflies in Tasmanian vegetable gardens – Know your enemy!

An important part of our Horticulture Certificate courses is pest identification and control.  Our students get to know Cabbage White Butterflies very well indeed!

Anyone growing vegetables in Tasmania at home or in larger production models, knows the Cabbage White Butterfly and the damage it can do to your crops. Controlling this pest is about getting to know your enemy!

Identifying Cabbage White Butterfly:

Generally in Tasmania we see the Cabbage White Butterfly being most active in the warmer months in spring through to autumn although they can be active on warmer days in winter as well.

Cabbage White Butterfly Male and Female.  Ref: www.sabutterflies.org.au

Cabbage White Butterfly Male and Female. Ref: www.sabutterflies.org.au

The Adult stage of the Cabbage White Butterfly is easily recognised. The large butterfly has yellowish white wings with a span of about 45mm. There is a black tip on the forewings and the base of the wings. The males have one black spot on the forewing and the females have two spots.

The Eggs are pale yellow and spindle shaped and usually laid singly on the outer leaves of the host plant.

The larvae of the Cabbage White Butterfly Ref: www.theearthconnection.org

The larvae of the Cabbage White Butterfly Ref: www.theearthconnection.org

The Caterpillars (or larval stage) are usually bright green with faint yellow stipes down the back and along each side. They will grow to around 30mm.

The Pupae are about 18 mm long, grayish brown, yellow or green and are usually attached to the undersides of the older leaves of the host plant or to some nearby object.

The Cabbage White Butterfly Life Cycle:

We tend to notice the large white butterflies flapping around out tender green vegetables and we certainly notice the damage done by their caterpillars, but knowing the whole life cycle of this loathed lepidopteron can make targeted pest control a lot easier and more effective.

The adult butterflies lay their eggs on the outer leaves of the host plant. The eggs hatch within approximately 4 days of being laid.

Cabbage White Butterfly Eggs.  Ref: gardener.wikia.com

Cabbage White Butterfly Eggs. Ref: gardener.wikia.com

The larvae go through several growth stages (instars) and become increasingly bright green n colour. They are voracious feeders during this time and will leave a trail of frass (dung pellets) behind them. They feed openly during the day and when they are resting they will align themselves with main veins in the host plant for camouflage.   The larval stage lasts around 27 days.

The larvae then pupate in angular elongate casings for a period of around 8 days. The pupa is approximately 17mm long and will attach to the host plant or surrounding vegetation or structures like fences. The colour of the pupa will roughly match the structure it is attached to.

The angular elongate pupae.  Ref: fay.iniminimo.com

The angular elongate pupae. Ref: fay.iniminimo.com

In the right conditions the entire life cycle can be completed in 3-4 weeks.

Cabbage White Butterfly Damage:

The majority of the damage done by Cabbage White Butterflies is done during the larval stages while the caterpillars are eating as much as possible before beginning to pupate. They will start by scouring the leaf surface and eventually devour the whole leaf and tender growing tips and shoots.

Damage done by caterpillars of the Cabbage White Butterfly.  Ref: smallholdingpleasureorprofit.blogspot.com.au

Damage done by caterpillars of the Cabbage White Butterfly. Ref: smallholdingpleasureorprofit.blogspot.com.au

What plants are effected by Cabbage White Butterfly?

A good basic list can be found at www.sabutterflies.org.au

This is an excerpt from that list.

The butterfly requires hostplants containing mustard glycosides.  These include most plants of the Brassicaceae family including *Alyssum spp, *Arabis spp (rock cress), *Barbarea spp (wintercress), cruciferous crops *Brassica spp (broccoli, brussel sprouts, cabbage, canola, cauliflower, mustard, radish, rape, turnip),*Cakile spp. incl. *C. edentula (American sea-rocket) and *C. maritima (Two-horned sea-rocket, *Cardamine spp (bitter cress), *Cardaria draba (hoary cress), *Descurainia sophia (flixweed),  *Diplotaxis tenuifolia (Lincoln Weed), *Eruca sativa (purple-vein rocket), *Erysimum spp (mustards), *Hesperis spp (rocket), *Hirschfeldia incana (buchan weed), Lepidium spp incl. *L. africanum (peppercress), *Lobularia maritima (sweet alyssum), *Lunaria spp (honesty), *Matthiola incana (common stock), *Raphanus sativus (radish), *R. raphanistrum (wild radish), Rorippa spp incl. *R. nasturtium-aquaticum (watercress), *R. palustris (yellow cress), *Sisymbrium spp. incl. *S. irio (London rocket), *S. officinale (hedge mustard) (Brassicaceae); also *Capparis spp, Cleome spp incl. Cleome viscosa(tickweed) (Capparaceae); *Reseda spp (mignonettes) incl. *R. odorata (sweet mignonette) (Resedaceae); *Tropaeolum spp(nasturtiums) incl. *T. majus (Tropaeolaceae); *Nicotiana tabacum (tobacco) (Solanaceae).

Controlling Cabbage White Butterflies:

There are literally hundreds if not thousands of different home remedies, cultural controls, chemical controls, traps, decoys and devices out there claiming to be effective against this pest. The short answer to the problem is to do what works for you and what fits with your own gardening philosophy.

Here are some of the more common remedies and methodologies in use in Tasmanian vegetable patches.

Chemical Control:

DIPEL is a product from Yates, available in nurseries and hard wear chains.   It is also called “Natures Way Caterpillar Killer”.   It is a powder you dissolve in water and spray onto your plants when you first see the caterpillars. Dipel contains Bacillus thuringiensis which is a biological control in the form of a bacterial stomach poison for all caterpillars. The caterpillars die within 3-5 days of eating treated foliage. It is totally safe to beneficial insects, bees, and mammals. Bt is broken down by sunlight within a few days, so repeated applications may be necessary. There is no withholding period with Dipel, so vegetables can be washed and eaten straight away.

ECO-NEEM is a registered organic insecticide for the control of a broad range of chewing and sucking insects including: caterpillars, curl grubs, aphids, mites, lawn armyworm, citrus leafminer, whitefly and fungus gnats in soil.   It is made from extracts of the neem tree (Azadirachtin A & B) and mixed with other plant oils to enhance it’s stability and shelf-life. It works by restricting caterpillar appetite and stopping larval development. Eco-Neem is currently approved in Australia for use on ornamental plants only but overseas it is approved for use on edible plants with no withholding period eg in New Zealand, Europe, UK, Japan and USA.

Biological Control:

Encouraging and even introducing beneficial insects like lace wings, lady birds and parasitic wasps into your garden can control caterpillar numbers by predating the egg and larval stages.

Mechanical Control:

Pick and flick: The simplest way of controlling Cabbage White Butterfly larvae is to pick them off and squish them or feed them to the birds. This may not be practical with larger infestations though!

Make a barrier: Put a physical barrier (netting) between your plant and the adult butterfly to stop her laying eggs on your plants in the first place. Bird netting and fine aviary wire are good for making “cages” or cloches out of.

Another of our Cloches with 4 hoops over a slightly longer bed.

A simple Cloche made with small aviary wire to protect brassicas.

Cultural Control:

There is evidence to suggest that Cabbage White Butterflies need to touch down on two successive suitable host plants in a row before they will lay their eggs. This makes sense from an evolutionary point of view as it ensures the larvae will have enough food to survive to the next generation and pass on their genes. So mixed plantings can be used to stop the adults getting those “two in a row” touch downs.

Decoys:

Many gardeners make small fake butterflies out of white plastic and string or post them up around their crop. This relies on the territorial nature of the adult butterflies. The theory is that they don’t lay their eggs where others have already laid theirs. So the butterfly thinks there is a big resident population (the fakes) and moves on to another area to lay her eggs.

A simple cut out decoy.  Ref: foodgardengroup.blogspot.com.au

A simple cut out decoy. Ref: foodgardengroup.blogspot.com.au

Another method is to lay egg shells around your plants. The theory here is that the butterflies prefer to lay their eggs on the broken shells. You then pick them up every 4-5 days and throw them away.

Any method that works for you in your own garden is a winner. Let us know what you do to make sure your veggies stay caterpillar free!

References:

www.dpi.nsw.gov.au/

www.sabutterflies.org.au

www.greenharvest.com.au

 

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