Caterpillar (Thanks to Sarah Walker)
Caterpillar (Thanks to Sarah Walker)

Many members of the insect Order 'Lepidoptera' (butterflies and moths) are agricultural pests during the immature or larval stages. These young are known as 'caterpillars', and include heliothis, cut worms, webworms, armyworms, Cabbage white and Cabbage moth or Diamond -back moth, to name just a few.


In the home garden, caterpillars can be removed by hand. They may be hard to see, as they are often green in colour. Hand picking is therefore best done in early morning and evening, when the caterpillars are most active. The cutworms are night feeders, hiding in the soil during the day. They are best picked in the dark hours.

A common safe biological control is Bacillus thuringiensis (B.t.) - sold as Dipel´┐Ż and other products. It is a bacterial spore, which only grows in the gut of Lepidoptera larvae (butterfly and moth larvae). It works very quickly as an anti-feedant (it stops them feeding) and eventually kills them. Be sure to spray under the leaves of plants, in the cooler part of the day. For cutworms, also spray the soil at the base of plants.

Other very useful biological controls include most of the generalist predators (spiders, assassin bugs, ground beetles etc), parasitic flies and especially parasitic wasps of the Braconid and Trichogramma groups.

There are viral diseases, fungi, and nematodes that may reduce caterpillar numbers dramatically when conditions for their spread are ideal.

Inter-planting techniques are also useful to confuse moths. Monoculture encourages pests, because they have to spend very little time looking for host plants, and can feed more, grow quicker, mature earlier and therefore produce more generations in a season. Monoculture also provides a less attractive environment for beneficial insects and predators. Intercropping can act by simply making the environment more complex and less favourable for the pest, or by repelling and confusing the pest (eg garlic intercrop), or a s a 'trap' crop. An example of a trap crop is to interplant dill or mustard between brassica (cabbage family) plants. These plants have more desirable flavour compounds than cabbage, broccoli or most other brassicas - therefore the intercrop attracts the pest away from the main crop. Inter-plants can then be sprayed with the botanicals, or rogue to remove some of the pest numbers. Other suitable inter-plants are onion, marigolds and aromatic herbs (sage, savoury. southernwood, tansy, thyme, majoram, mint and rosemary). Red Cabbage has far fewer of the taste components that the adult moth is searching for when she looks for an egg-laying site. If you have trouble growing cabbage without severe caterpillar damage, try red cabbage.

Care must be used when inter-planting not to encourage the pest into the crop. Do not allow host plants that are not being actively used as inter-crop to flourish near the cropping area.

In very severe infestation areas, use floating row covers. They are light, fine woven mesh covers which are placed over growing seedlings. As the seedlings grow, they lift up the mesh. Enough light gets through, and air circulates, in fact there may even be desirable micro-climate modification under the cover (sun-scorch protection, temperature moderation, light frost protection, hail protection etc).

There are some very safe sprays, some which act more as a repellent than an insecticide. One of these is sour milk. Add 4 teaspoons of vinegar to a cup of milk and allow to sit for several hours. Wood ash also works - put it inside a stocking and shake the fines out through the weave.

Caterpillar (Thanks to Sarah Walker)
Caterpillar (Thanks to Sarah Walker)

Caterpillars are quite susceptible to a number of botanical insecticides, because of their soft body and veracious appetite (they take a lot of active ingredient in as they feed). Suitable pesticides are derris, quassia, garlic and chilli or pyrethrum (use pyrethrum with care for your own health and remember that it can harm beneficial insects too). The insecticidal (potassium) soaps also work, as may citrus oil, eucalyptus oil and some other essential oils - but be careful not to burn the plant or yourself with strong oil sprays. Use one of the very good commercial products available, or proceed very carefully if experimenting with use of these oils.

Cutworms have to climb up the stem of the plant. They can be treated with physical barriers such as vaseline or a slurry made from diatomaceous earth. You can also make the botanical insecticides, such as garlic spray into a paste with flour and place it around the stem.

Bug juice

The bug juice remedy may also work for caterpillars. This unwholesome sounding spray is made by blending a handful of the pest insect with two cups of water of milk. Let the brew sit for a few hours and spray over the plants. It is uncertain exactly how this spray works, but there are a few possibilities:

  • It spreads the spore of entomophagous fungi, bacteria, nematodes or viral particles, which infect the insect

  • It releases scents which attract predators

  • It releases scents which discourage the pest

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