Organic Strategies for Caterpillar Control
© Frances Michaels
Caterpillars generally eat leaves but some feed inside fruit such as Codling Moth and Budworms. The types that
feed on leaves are easiest to control organically. Common pests in this group include Cabbage white butterfly
(pictured), Cluster caterpillar, Cabbage moth, Grapevine moth, Loopers, Light brown apple moth and Lawn armyworm.
The eggs of caterpillars are usually laid on the underside of leaves. Caterpillars are good at hiding themselves,
so usually it is leaves chewed full of holes that you notice first. Dark green droppings on a leaf are another
giveaway. Look carefully along the leaf veins and on the underside of the leaves for the culprits. Running your
fingers lightly under the leaf will usually cause enough movement to allow you to spot a well-camouflaged insect.
Before developing your pest management strategy, decide if you really need to do anything at all? Is it a plant
you care about; is the damage sufficiently bad to warrant your intervention? For example, the beautiful Large
Citrus butterfly does very little damage to citrus trees, losing a few leaves seems a small price to pay for
having it in your garden. If the answer is yes, then choose from several of the suggested physical, biological
and least-toxic chemical controls. Organic gardening relies on several overlapping strategies rather than the
power of a single highly toxic chemical to kill the pest.
General Physical and Cultural Controls
Handpicking is useful and very effective particularly if only a small number of plants are being attacked.
Every caterpillar removed is one less moth laying eggs in the weeks to come. Carry a small bucket into the
garden with you to collect caterpillars and other pests as a treat for your chooks.
Keeping a garden diary will help you to remember what not to plant! If a plant is being consistently attacked,
try planting at a different time, taking earlier preventative measures or just not planting it at all. Strangely
enough just planting a different colour can help, Cabbage White Butterflies are less likely to lay eggs on
non-green Brassica so you can try
red bok choy
Control Strategies for Cabbage White Butterfly
The Cabbage White Butterfly is a major pest of Brassica species (broccoli, cabbage, cauliflower, Asian greens)
world-wide. It does a lot of damage early in the season as young plants have their growth set back by losing so
much leaf area.
Cabbage White Butterfly has a territorial behaviour pattern and this can be used against it. The theory goes that
if it appears that many Cabbage White Butterflies are already present it will leave the area looking for less
populated plants to lay its eggs on. So setting up decoys can help:
Exclusion and Netting
- A butterfly net is a surprisingly useful addition to your garden tools. It takes a bit of practice to catch
Cabbage White butterflies but is an effective way to reduce numbers.
- If you can prevent moths from laying their eggs in the first place then you are way ahead. You can exclude
caterpillars by using a fabric designed to cover vegetables such as a
or make innovative use of mosquito netting or old window screens.
Companion planting is used both for pest control and to encourage plants to grow well.
General Biological Controls
- Insectary flowers to feed the good bugs:
buy Good Bug Mix here
- Trap crops to re-direct the egg-laying onto non-crop plants. In some cases these can be more attractive
to the Cabbage White butterflies than the crop itself such as dill, nasturtium and mustard. Trap crops can
also retard larval growth or actually kill the tiny caterpillars when they try to feed. Upland Cress has
been shown to be an effective dead-end trap crop for several common pest moths and butterflies. Upland Cress
leaves contain high levels of saponins and glucosinolates that attract the moths. The moths then lay their
eggs on the leaves but when the caterpillars hatch, the larvae take a bite of the leaves and die.
- Living mulches confuse the adult moths and butterflies and make it difficult for them to find the crop.
Examples of this include using white clover under crops of broccoli and cabbage. The crop plants need to be
planted ahead of the living mulch to allow growth to take off without competition. It is believed the living
mulch works in several ways, partly by masking the smell of the crop and partly by changing the appearance of
the crop, especially the light levels. A groundcover such as
is also very attractive to beneficial insects.
- Repellent plantings to make the area undesirable to the pests. Strong smelling herbs with pungent smells
have been used traditionally in both the garden and the home to keep moths at bay. Use hardy herbs suitable
as a hedge around the vegetable garden such as wormwood, southernwood, sage, lavender and rosemary.
Enhancing the environment for the natural predators of caterpillars is a long-term strategy with the benefits
increasing over time.
Least-Toxic Chemical Controls
- Start by attracting small insect-eating birds by providing safe nest sites and a constant supply of water.
Dense plantings of native shrubs, in out-of-the-way corners will provide nesting sites; prickly shrubs give
added protection from predators.
- Nesting boxes for birds can fulfil an urgent need created by habitat destruction.
- Insect predators of caterpillars include: assassin bugs; tachinid flies; paper wasps, which chew up
caterpillars and feed them to their larvae; lacewings and ladybirds eat moth eggs; tiny trichogramma wasps
parasitise moth eggs; other tiny wasps like Apanteles sp. parasitise the caterpillar, the wasp larvae feed
on non-essential parts of the caterpillar. When the wasp larvae are ready to pupate their exit generally
finishes off the host caterpillar. Sounds gruesome but it is a part of nature.
Choosing a least-toxic spray will reduce the impact on your good bugs!
contains Bacillus thuringiensis,
or Bt for short; it is highly effective and selective against most species of caterpillars. This biological
control is a bacterial stomach poison for all caterpillars, which is mixed with water and sprayed onto foliage.
It must be ingested by the actively feeding caterpillar, which dies 3-5 days later. 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.
Amgrow Tomato and Vegetable Dust
Sticky Yellow Traps