From: Al Cooke
Sent: Fri, July 8, 2011 9:39:44 AM
Subject: Re: Needing advice with our Leland Cypress
Re: Needing advice with our Leland Cypress
“twitching cocoons” on a Leyland cypress are probably bagworms. You may want to confirm that by comparing with pictures at
http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/ort081e/ort081e.htm
The cocoon is generally broadest in the center, narrowest on both ends, and covered with vegetation from the host plant.
Bagworms have one generation per year making it pretty easy to estimate their current stage of development and to predict how and when development will progress. Generally by early June all eggs have hatched and it’s easy to kill the young caterpillars with organic sprays such as B.t. (Biobit, Dipel, Foray) or spinosad (Conserve). Later in the summer as they mature and feed less it will likely require a synthetic product such as Orthene, Sevin, or Mavrik. Since you can observe them twitching, it’s probably not too late for the organic products. But you should deal with them soon or plan on losing another plant eventually.
It’s always appropriate, if not always practical, to remove the cocoons by hand. By late summer, mature males will leave the cocoons, find a female, and mate. Females never leave the cocoon, lay eggs after mating, and die there. Cocoons left by the end of summer are either empty (vacated by a male) or contain hundreds of eggs that will start hatching about next May. From June to early August is the only window for effective treatment with insecticides. Hand removal of the cocoons is always appropriate.
Typically, bagworms do a little damage in the first year on a plant and a lot in the second year; few plants survive a third year of feeding. Leyland cypress has become one of the favored plants but junipers and arbor vitae are also prime targets.
alcooke
Al Cooke
Extension Agent, Horticulture
Chatham County Center, N.C. Cooperative Extension
PO Box 279, Pittsboro, NC 27312
919.542-8202; Fax 919.542.8246
http://www.ces.ncsu.edu/chatham/staff/acooke/home.html