Whether it's a looper, a leafroller or a tenter, caterpillar species have the potential to wreak havoc in home gardens. These butterfly and moth larvae can feed voraciously, especially on foliage. Whether the species you're coping with turns leaves into skeletons or makes unsightly tunnels through the greenery, caterpillars have the potential to kill plants by stripping them of their crucial foliage.
- Keeping plants healthy by maintaining appropriate watering and feeding schedules for each plant is key in helping them withstand damage wrought by caterpillars.
- Branches or stems that have signs of caterpillar nests or eggs can be cut away and disposed of before a new generation emerges. Similarly, if you see signs of caterpillar eggs on the trunk of a tree, rub them off the bark and dispose of them.
- A botanically diverse yard can also help control caterpillar populations. That's because plants such as yarrow (Achillea millefolium, U.S. Department of Agriculture plant hardiness zones 3 to 9) and annual dill (Anethum graveolens__) attract the insect predators that keep caterpillar populations down.
To prevent caterpillar moths from laying eggs, consider setting a floating row cover, or other landscape fabric system, over your vulnerable plants. For this method to be most effective, conduct a little investigative work into the types of caterpillars most likely to target the plants you're concerned about, including when they're normally in the egg-laying stages. Handpicking caterpillars from plants and then dropping them into soapy water is another a tedious but foolproof way of reducing current caterpillar damage.
Bacillus Thuringiensis Sprays
The University of California's Integrated Pest Management program recommends applications of Bacillus thuringiensis, a naturally occurring bacterium sold for use as a pesticide. Bt is available in concentrated doses, such as granular form.
Read package directions carefully. The label will likely give the exact recommended dose, which is usually between 1 and 4 teaspoons of Bt per 1 gallon of water but depends on the plant you're treating.
Add the amount of Bt you're using to a 1-gallon bucket of water, and stir vigorously. Add a "sticking agent" such as a spoonful of molasses to the bucket, and stir again.
Pour the Bt blend into a backpack sprayer, hose-end spray system or spray bottle.
Coat the foliage of the plants you're treating so that they are well moistened but not dripping wet. Spray both the upper and the lower sides of leaves.
Shake the vessel holding the Bt frequently when moving from plant to plant to keep it well mixed.
Repeat the spraying process about once a week, and after rain, while you are still seeing some damage.
Additional options for treating caterpillar infestations include ready-to-spray synthetic treatments. As with Bt, application directions for products containing insecticidal ingredients such as permethrin vary depending on the plants you need to treat. Some edibles may be treated on the actual day of harvest, while others might need to be halted three weeks prior to expected fruit or vegetable maturity. The label also gives instructions for how often to spray various ornamental and edible plants.