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.
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! Any plant consistently attacked should be
planted at a different time, preventative measures taken or not planted at all.
Large pieces of eggshell can be scattered amongst cabbages to confuse the Cabbage white butterfly. The theory
goes that it will mistake the eggshells for other butterflies and leave the area looking for less populated
plants to lay its eggs on.
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 or make innovative use of mosquito netting or
old window screens.
Enhancing the environment for the natural predators of caterpillars is a long-term strategy with the benefits
increasing over time. Attract 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.
Least-Toxic Chemical Controls
Choosing a least-toxic spray will reduce the impact on your good bugs!
can be used as
a repellent and to kill caterpillars.
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