Last week, your evergreen tree looked lush and green. Now it's been turning brown and decorating itself with little seed cones. What the heck is going on? As always, Grumpy has the answer.
Those seed cones aren't really seed cones. They're the foliar apparel worn by an insidious caterpillar called the bagworm. Tiny bagworm caterpillars, about a quarter-inch long, hatch in spring. When they locate a tree or shrub they find tasty, they build cone-shaped bags made from silk and the foliage of the plant they're currently eating in order to hide from predators. They dine happily all spring and summer, until by fall they're up to 2 inches long. Just before they die in fall, female bagworms lay up to 1,000 eggs in each bag to start the cycle all over again the next spring.
What are their favorite delicacies? Well, bagworms will eat deciduous plants, but they really prefer needleleaf evergreens, such arborvitae, false cypress, Leyland cypress, juniper, and spruce. Bagworms are voracious gluttons -- unless controlled, they'll quickly strip an evergreen of its foliage and may kill it.
Bag Those Bagworms! The most common error gardeners make is not recognizing the problem early enough and misidentifying the bags as "pine cones." Only pines have pine cones. The minute you see browning needles and pine cones on things that aren't pines, pick off the bags and stomp them. If the bags are too high to reach, spray the foliage with a wide-spectrum insecticide such as Spectracide Triazicide or a natural insecticide such as neem oil, spinosad, or Bacillus thuringiensis (Bt). You can get all of these at the garden center.