Question: What can I do about bagworms eating my Leyland cypress trees?
Answer: If your Leyland makes it through the wind and rain of tropical storm Andrea, then you will have to defend against bagworms.
While Leyland cypress trees are pretty and grow fast, they have a host of life threatening problems. Their three worst enemies are wind, disease and bagworms.
Bagworm eggs hatch toward the end of May or first week in June. These cute little worms are only 1/8-inch long. Instinctively, they begin to test the strength of their silk by spinning a silk thread and hanging around. Spring breezes catch the wee little worms and blow them to greener pastures. Green pastures for a baby bagworm is a long line of Leyland cypress trees.
If a bagworm is lucky enough to land on a suitable host plant, then it spins a silk cocoon. This cocoon serves as protection from predators, sunlight, pesticides, etc. Foliage from the host plant is cleverly incorporated into the silk cocoon. Bagworms were the original inventors of the ghillie suit (http://en.wikipedia.org/wiki/Ghillie_suit).
As bagworms feed on foliage, they grow and enlarge their silk protection. Homeowners finally begin to spot these pests in August or September. By then, the feeding damage is very obvious and the caterpillars are difficult to kill. Since young caterpillars are easy to kill, launch the pesticide assault in late May or early June.
Products containing Bt (Bacillus thuringiensis), like DiPel or Worm Whipper, are not contact insecticides. They have to be eaten by young caterpillars. Simply spray the Bt on the foliage and let the baby bagworms nibble. After a couple bites, they develop a stomach ache that won’t go away. This target specific, non-contact type of pesticide bypasses the protective cocoon and is very safe to the applicator and surrounding environment. However, it does not work well on mature caterpillars.
Contact insecticides like Sevin, Malathion or Orthene are also more effective when the caterpillars are young. By the end of August or September, bagworms are nearly invincible. Handpicking or a .22 rifle will work better than insecticides (depending on your aim).
For more information about bagworms visit http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/ort081e/ort081e.htm
If you don’t have internet access, call the Extension Office at 893-7530 or email me at gpierce@harnett.org.
Leyland cypress is one conifer that will grow a new pointy top if the top portion of the tree is removed. This means you can prune off the top third or half of the tree and it will eventually grow back to a pyramid shape. Reducing the height of these trees decreases wind damage potential and makes them easier to spray for bagworms.
If you don’t reduce the height then the bagworms will reduce it for you. Unfortunately, they typically reduce it to the ground.