A week ago, faithful reader Felisha Avery-Smith had a healthy, green Leyland cypress. Today, she has a brown, dead Leyland cypress. She wanted to know the cause, and wisely consulted the unimpeachable source for all gardening wisdom, your humble Grumpy Gardener.
One look revealed the answer – voracious, clandestine caterpillars called bagworms. Bagworms are the larvae of moths that lay eggs on the foliage. They get their name from using bits of the host plant’s foliage to construct sack-like bags around themselves to hide from predators, including you. They hang beneath the branch they’re feeding upon, leading some folks to mistake them for pine cones, even when the tree isn’t a pine. Bagworms usually appear at the top of the tree or shrub first and eat their way down. If they’re present in sufficient numbers, they can defoliate a plant in a week. Because evergreens store a lot of food reserves in their foliage, this damage can be fatal.
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Spruce, fir, cedar, juniper, arbor vitae, false cypress, Leyland cypress, pine, and other conifers are favorite targets. However, bagworms will feed on deciduous plants too, such as honeylocust. As I indicated, the first sign of their presence is browning of the top branches. If there are but a few bagworms, pick them off and smash them. A major infestation, though, requires spraying the tree or shrub with Triazicide according to label directions. You can get this at home and garden centers.
Put the bag on bagworms. Your tree will thank you for it.