Well, the white cabbage butterflies are out in full force now so letâ€™s make a pact to beat them this year.
Back yard cabbages, cauliflowers, broccoli, kale, Chinese cabbage and brussels sprouts are in danger of being gobbled up by the butterfly babies, those hungry green caterpillars. Itâ€™s not a pretty sight, and besides, who wants to eat a cabbage thatâ€™s been munched and pooped on.
Most caterpillars are harmless native caterpillars and donâ€™t need to be controlled. The ones we donâ€™t like are those that cause the most damage to our brassicas. These are the offspring of the Large and Small White Cabbage Butterfly (Pieris brassicae and Pieris rapae) affectionately know as the summer snowflake, though Iâ€™m not sure who feels affection towards them.
The White Cabbage Butterfly
The White Cabbage Butterfly isnâ€™t a native butterfly. It was accidentally introduced in 1937 and has grown into a major problem, especially for us back yard veggie gardeners. You can identify it easily by the white with black spots on its wings. The females have two black spots and the males have one black spot.
The most effective way to control cabbage butterflies and other pests is not to resort to a quick chemical cocktail but rather, to mobilise an integrated pest management approach, including cultural control, mechanical control and biological control.
Integrated Pest Management
STEP ONE â€“ Know your enemy.
A healthy plant is less susceptible to pests and disease so build your knowledge base about what your vegetables need to grow and be healthy: reducing transplant shock, rich soil, regular fertilisers, compost, mulch, companion planting, crop rotations etc...
Know the damage characteristics of caterpillars (symptoms and signs of infestation) and check that your problem really is caused by caterpillars. If you can see slimy trails on and around your brassicas, the cause may be snails and slugs. Or, you may have them all.
Itâ€™s also helpful to understand the life cycle and history of the critters.
STEP TWO - Prevention.
We donâ€™t enjoy harming creatures, especially caterpillars, so our first strategy is always prevention.
STEP THREE â€“ Observe.
- Fine mesh or mosquito netting draped over the plants is the most effective line of defence. Youâ€™ll need to drape it over a frame so the netting isnâ€™t in contact with the plants as they can land on the netting and lay eggs on the leaves. Peg the netting down at soil level to prevent the butterflies sneaking underneath. Yes, this is war.
- Plant companion plants that help to draw the white cabbage butterfly to other plants and away from your brassicas. Nasturtiums and marigolds are effective â€˜sacrificial lambsâ€™ and better that the butterflies lay hungry babies on these than on your food crops.
- Strongly scented herbs such as dill, sage, oregano and rosemary can be interplanted to discourage the butterflies from alighting in your brassica patch.
- Including biodiversity in your food garden will work to your advantage by confusing the butterflies. They are less likely to descend in droves if your garden has a variety of plants in different sizes, colours, shapes, scents in the same area. One entire patch of brassicas with nothing else in it is the proverbial â€˜sitting duckâ€™ of the veggie patch.
- Scatter â€˜Good Bugâ€™ seeds all over your garden to provide food and habitat for beneficial insects and natural predators such as the parasitic wasp and ladybirds and natural predators in your garden. Free pest biocontrol.
- Encourage birds into your garden with a diversity of trees, shrubs, flowers, bird feeders and a bird bath. Many bird species will eat caterpillars
- Try tying strips of white fabric to canes or trellises above or near your brassicas. This Is supposed to resemble butterflies with wings that flap in the breeze and may trick butterflies into thinking that your plants are already populated. You can also buy ornamental butterflies that flutter on sticks in the garden which do the same thing.
Monitor your plantsâ€™ progress regularly and thoroughly and look for symptoms and signs of caterpillars.
The lovely thing about growing vegetables is wandering around the garden and observing the progress of your seedlings. Through micro-observation you can also detect the smaller life-forms that populate your garden too - worms, ants, insects, bees, beetles and spiders for example. Itâ€™s fascinating to watch the interplay between the beneficial and not-so-beneficial critters.
Observation is critical to understanding whatâ€™s happening in your food garden.Itâ€™s also critical in the war against those green grubs.
Itâ€™s easy to see the green caterpillars on red/purple cabbage, but on green leaves theyâ€™re perfectly camouflaged so you need to sharpen your eye to find them.
- Observe the white cabbage butterfly hovering around the garden. Where she lands is probably where she wants to lay her eggs.
- Observe if there are any holes in your brassica leaves. If they are small holes, youâ€™ll find very tiny caterpillars on the plant. If they are huge holes or entire leaves have been eaten, youâ€™ll probably find big, fat caterpillars feasting away.
- You can also tell if caterpillars are hiding amongst the leaves by the size and freshness of their green droppings (frass)
- If you check your brassicas daily (use a magnifying glass if you need to), you may even find the larvae on the top or underside of the leaves, before they hatch out and start munching.
- Use a small mirror attached to a lightweight stick to look under the leaves.
STEP FOUR - Decide on Intervention and Control.
Biological Control â€“ Mother Natureâ€™s hit squad â€“ wasps
Mechanical Control â€“ simply pick the caterpillars off every day.
Unfortunately if your brassica leaves are disappearing by the minute, you may not have enough predators in your garden to control the infestation. The only way to stop the destruction quickly is to physically remove the hungry caterpillars by hand and â€˜relocateâ€™ them, preferably to the chooks.
If you have a strong stomach, just squish them. This has the additional benefit of repelling other insects as the dying caterpillars emit a â€˜fear pheronomeâ€™ that has a strong aroma signalling danger.
Caterpillar control is a great exercise for kids. Get them to check the cabbages and caulis every morning, find the caterpillars, pluck them off and put them in a container. They can put holes in the lid, feed the hungry critters a few leaves, and watch whatever happens. Great!!! The caterpillars are safely behind bars AND quality nature education time for the kids. You might like to give your child a butterfly net with instructions on catching white butterflies only!
Be careful that they donâ€™t destroy the beneficial insects.
Keep a keen eye out for the unhatched larvae as well. You can relocate the fluffy bundle to the organics or compost bin without their food source and after hatching, the baby caterpillars will naturally starve.
STEP FIVE â€“ Maintain your own control.
Itâ€™s easy to over-react when you see your seedlings and veggie plants being chewed on by caterpillars. If you only have a few, itâ€™s probably better to leave them alone so that Nature can do her job of balancing the pest/predator ratio.
STEP SIX â€“ Record outcomes for future reference.
Keep a gardening diary and record when the white butterflies started appearing. That way you can be prepared next year and take preventative action in good time (eg. plant your Dill earlier). Record what you did this year in the war against the white cabbage butterflies and their green babies. How well did your control work?
And please, feel free to share with us any organic practices you have that help control the white butterflies and their green caterpillars. Weâ€™d love to hear from you!!!