Understand your pests
I regularly encourage gardeners to actively plant and garden to encourage butterflies and my garden is filled with delightful butterflies which flit about and delight us. However there is one butterfly that I don’t appreciate and that is the cabbage white butterfly. It lays its caterpillars on many of my vegies and they make a mess of the foliage and cause the children to screech if I accidentally miss one and it gets cooked up and served with the broccoli!?
To deal with these troublesome pest butterflies and their caterpillars we must first understand them. They are definitely more of a problem in the warmer weather of autumn and spring than they are in winter. Their blue-green caterpillars love to eat Brassicas such as cabbages, broccoli, Brussel sprouts, Chinese cabbages, cauliflower, celery, beetroot, rocket and Asian greens such as Bok or Pak Choy. Also, they are more likely to make a mess of young plants, plants under stress and plants growing in poor soil rather than they are strong healthy, robust plants grown in good soil.
If you see them buzzing around your patch, there are a number of options to help deal with them. I have seen a few swifty gardeners simply clap their hands or skillfully swipe at them and wipe them out, but I find my reflexes are simply not that good, and I think this did nothing more than make them laugh!?
Personally I think this is the best option as the butterfly is unable to lay its eggs onto the leaves in the first place. I use insect exclusion netting net which looks similar to shade cloth and is flexible so it can either be draped loosely over growing crops and secured around the edge, or stretched over arches made of poly pipe. The main thing with using this mesh is to make sure it is held in place securely as every now and then I find I have been slack and a butterfly has walked in under a loose edge, and then not be able to get out!
If you inspect your crops regularly this can be remarkably effective. Collect them and either squash them by hand (preferably in gloves as they make a green squishy mess on your fingers) or feed them to your chooks.
Deter the butterflies from laying eggs on your plants by placing pretend butterflies around your patch. Apparently cabbage white butterflies are territorial and won’t alight on plants if they think there are already other cabbage whites in the area. These can be butterfly shapes made from white plastic containers and nailed to short bamboo stak
es or strips of white shopping bags tied into bows on bamboo stake. You need to place quite a few around a bed, somewhere between two and four per square metre. Other friends have cut Styrofoam boxes into cubes or used Styrofoam packing beads and threaded them on fishing line and hung them around the area. Some people find this technique very effective and others don’t. A lot could come down to having healthy plants in good soil versus plants under stress however in my experience there is less damage than there would have been otherwise.
Plant landcress as a companion plant.
I have grown this herb in my vegie patch for years and never noticed this effect however this year I am trying a plant inbetween a number of unprotected brassicas to see how it goes. A colleague on Gardening Australia has filmed a short clip on how it works at http://www.abc.net.au/gardening/stories/s4197010.htm. The cabbage white butterfly is attracted to lay its eggs on the cress rather tha
n your brassicas. When the caterpillars hatch they munch on it and die.
Non toxic spray
Spray with a nontoxic bio-insecticide containing Bacillus thuringiensis such as Dipel which kills the caterpillars without affecting other beneficial insects. This is not a UV stable spray however so if you use it in the morning it will have broken down by the afternoon. It best to apply it in the late afternoon so that it remains on the plants for the longest time and is most effective.
Some gardeners swear this works as if you leave egg shells scattered around young plants and the butterflies get confused and lay their eggs on the eggshells. Collect them up once a week, inspect them for yellow eggs and then crush them and add them to your compost bin.
Do nothing and wait for the cavalry.
There are a number of natural predators and parasites of the caterpillars so look out for evidence of these creatures at work in your patch. They include a parasitic wasp which lays its eggs inside the caterpillar and then spins a gossamer sack around the caterpillar which is eventually transformed into more parasitic wasps. However while I do see these in my garden there are never enough to rely on them wiping out the pest caterpillars.
Don’t stress and share.
To be honest I don’t worry too much about a few holes in the leaves, although it is not good when I am entertaining. I do keep a bottle of cider vinegar by my kitchen sink and add a splash to the water whenever I wash vegies to knock off any pests I may have missed. As gardening author of One Magic Square, Lolo Houbein, once told me “You can eat holes, they cook up really well!”
Find the option that suits you best and happy gardening!