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Pests in Gardens and Landscapes: Quick Tips

Caterpillars, the larvae of butterflies and moths, damage plants by chewing on leaves, flowers, shoots, and fruit and sometimes other parts of the plant. Caterpillars hidden in rolled leaves or among foliage can be difficult to see and manage. However, many plants, especially perennials, can tolerate substantial leaf damage, so a few leaf-feeding caterpillars often aren’t a concern. Handpicking and natural enemies often provide enough control.

Remove caterpillars early to prevent excessive damage.

• Look for feeding holes, excrement, webbed or rolled leaves, caterpillars, and eggs.
• Prune off rolled or webbed leaves and handpick caterpillars from plants. Destroy the insects by crushing them or by dropping them into soapy water.

Many "good bugs" eat caterpillars.

• Beneficial insects and other organisms often keep caterpillars under control..
• Most caterpillar species have several species of parasitic wasps or flies that attack them. Look for parasite cocoons next to or on caterpillars, darkened caterpillar eggs, or exit holes in dead caterpillars.
• General predators include birds, assassin bugs, lacewings, predaceous ground beetles, and spiders.
• Naturally occurring diseases caused by viruses, bacteria, or fungi often kill caterpillars.

What about pesticides?

• Use insecticides only when damage is intolerable, nonchemical methods haven't worked, and smaller caterpillars are present. Avoid insecticides that can kill beneficial insects. Don't treat butterfly garden plants, otherwise you'll kill the caterpillars that will become butterflies.
• Bacillus thuringiensis subspecies kurstaki (Btk) is a microbial insecticide that kills only caterpillars. It’s safe to use near bees, beneficial insects, and wildlife. Caterpillars must feed on treated leaves to be affected. Because Btk is most effective on small, newly hatched caterpillars and breaks down rapidly, treatment timing is critical.
• Spinosad is a microbial-based insecticide but can have negative impacts on some beneficial insects.

Some common leaf-feeding caterpillars

Beet armyworm is a common pest on vegetables and flowers. Yellowstriped armyworm is similar but dark with yellow and orange stripes.	A parasitic wasp lays her egg in an armyworm. The egg will hatch into a larva that will feed inside the armyworm and kill it.
Tobacco hornworm on tomato. Note its excrement on the leaf below.	The western tussock moth feeds on many ornamental and fruit tree species.
Leafrollers, such as this fruittree leafroller, feed inside leaf rolls secured with silk and often drop to the ground when disturbed, hanging from a silken thread.	The cabbage looper has three pairs of prolegs in the back, in addition to three pairs of legs in the front, causing it to move in a looping pattern.
Fall webworms feed in groups within silken tents. Many tent caterpillars create similar nests.	Egg cluster and newly hatched larvae of the redhumped caterpillar. As these larvae mature they will develop a bright red hump just behind their head.

Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.