How to Save Crops from Cabbage White Butterfly and Other Pesky Caterpillars

How to Save Crops from Cabbage White Butterfly and Other Pesky Caterpillars

Those white butterflies flapping merrily around your vegetable garden may look lovely and whimsical but they are the bane of most gardeners.  Once their eggs hatch into plump green caterpillars your crops leaves will slowly but surely develop ever increasing holes.  It’s not impossible to beat this plant predator but it does require planning and forward thinking to save yourself from an infestation where you have more holes in your vegetables than leaves.

Here are the methods that I’ve tried in my garden;

Decoys

I have heard that as White Butterfly are territorial, and do not like competition for their young, they can be warded off with decoys.  I painstakingly created a handful of decoy butterflies, painting realistic representation onto clear plastic and mounting them on wire in my garden.

This had no effect whatever.

This decoy did not fool the butterflies

I wonder whether these did not work because they did not have the characteristic irregular jerking movement of Cabbage Butterflies.  I may try this method again with a solar powered, flapping butterfly garden ornament that I have seen online.

Egg control by hand

Going into the garden every day and searching under every leaf to find and destroy the eggs.  The butterflies lay greenish yellow eggs on the underside of leaves, often spaced well apart.

Once you get the hang of it you can spot and gently crush the eggs with your fingers.

Small, green yellow egg on underside of leaf

This method does work to keep caterpillar numbers low but you will inevitably miss some and it is a time consuming job.

Vegetable netting

Protect your vegetables with bug netting.  This is another simple technique, simply cover your crops with a fine mesh netting.

Vegetable netting, safe and effective

Netting your vegetables works if you put them in place before planting seedlings or before the butterflies emerge for mating season.

You can use special connectors for bamboo poles to make a frame or simply put old seedling pots over the end of garden stakes for support.

I have also seen one inventive gardener who used old brooms, she stuck them bristles up into the soil around her vegetable patch to support the netting above her plants.

Sacrificial crops

Find a plant that caterpillars love and plant it around your vegetable plot as a sacrifice.  The Cabbage Butterfly will lay their eggs into this crop and their larvae will happily munch their way through it and leave your vegetables alone.

There’s no guarantee that the butterflies won’t lay eggs amongst your vegetables as well as the sacrificial crop.

Sacrificial crop

The caterpillars that do hatch on the sacrificial crop don’t seem to wander far from the leaf they’re hatched on.

Rocket (Arugula) and Nasturtium have worked well for me.

Biological control

Dipel

Some of my crops are too big to net, such as indeterminate tomatoes, in such cases I sometimes turn to DiPel.

Dipel is a bacteria (Bacillus thuringiensis) that is sold in the form of a powder that is added to water and sprayed over crops.  Only the caterpillars that eat the sprayed leaves are affected so if you like to encourage butterflies in your garden, they can still safely raise their young amongst your ornamentals and unsprayed plants.

The bacteria causes paralysis of the stomach in caterpillars and they will stop eating and starve to death.  It only affects caterpillars and is safe for all other garden visitors including humans, crops can be picked, washed and eaten at any time after spraying.

Once a caterpillar has eaten a Dipel sprayed leaf it will cease to eat but may take several days to die.

I have read that some gardeners find that Dipel is mainly effective against small or young caterpillars.

Parasitic Wasps

If you find small yellow cocoons in your garden, you may have the parasitic wasp, Cotesia Glomerata. 

These parasitic wasps are the  size of a flying ant or small fly, the adult feeds on nectar.

Parasitic wasp cocoons

Cotesia Glomerata lay their eggs inside caterpillars which then hatch and feed on the internal organs of the host, whilst keeping it alive, until they are ready to pupate.  Once the wasp larvae are ready to pupate the caterpillar will spin a protective webbing around itself and the larvae and then die.

The parasitic wasps will reduce the number of White Butterfly in your garden as the caterpillar dies before metamorphosing but it does not reduce the number of caterpillars in the short term, an infected caterpillar may even eat more than an un-infected caterpillar so your crops are not saved.

 Results

Beating the hungry, hungry caterpillars in your garden can be done but you need to start measures at the first sign of the butterflies because they will soon mate and lay their eggs all through your garden.

I use a combination of netting, removing eggs and caterpillars by hand and spraying with Dipel.

A few holes in your crops is a sign of a nice organic garden but a skeletal plant will not be providing much food for you and your family.

“Gazebos aren’t for gardeners. They’re for other people, because do gardeners ever really sit?” – Tony Avent, Horticulturalist 

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