How to Treat a Caterpillar-like Insect on a Leyland Evergreen

If you notice caterpillar-like insects on your Leyland cypress tree (Cupressocyparis leylandii), they're most likely bagworms. The evergreen Leyland cypress grows in U.S. Department of Agriculture plant hardiness zones 6 through 10, and it's an ideal host plant for bagworms to infest. Bagworm larvae, or caterpillars, eat the needles, which can slow the tree's growth or even kill it in extreme cases. The caterpillars are between 1/8 and 2 inches long. They carry cone-shaped bags made from silk and plant material that are up to 2 inches long, and they look similar to pine cones. They go inside their bags once fully grown to pupate into moths. It's possible to control bagworm infestations by hand or with microbial insecticide if they're caught early.

Bucket
Dish detergent
Gloves
Sealable plastic bags
Ladder
Garden sprayer
Bt liquid concentrate
Insecticidal soap
Permethrin
Horticultural oil
Neem oil

Instructions

- 1
  Fill a bucket with water and a few squirts of dish detergent. Put on a pair of gloves.
- 2
  Handpick the bagworms from the tree if they're within reach and few in numbers. Place the bagworms in the bucket of soapy water. If you use a ladder to reach the bagworms, carry a sealable plastic bag and place the bagworms in it. Seal the bagworms in a bag and dispose of them in the garbage. This method is the most effective when performed during the winter or early spring.
- 3
  Mix Bt (Bacillus thuringiensis) liquid concentrate with water in a garden sprayer according to the amount specified on the label.
- 4
  Spray the foliage, branches and all parts of the tree with the Bt solution on cloudy days or in the later afternoon or evening. Do this in spring, preferably May, before the bagworms become larger than 3/4 inch. Reapply the Bt in two weeks.
- 5
  Spray the foliage, branches and all parts of the tree with insecticidal soap, permethrin, horticultural oil or neem oil if the bagworms are more than 3/4-inch long. If you use a concentrate, mix it with water according to the amounts specified on the label and follow any safety precautions. Reapply as needed according to the label.

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