Question
Hi Jim,  
We noticed something in our blue spruce and we have been told they are bagworms.  We have picked as many as we can reach off of the tree, but the tree is 2o to 25 feet tall.  How can we save our beautiful trees?  Any suggestions you can give us would be greatly appreciated.

Answer
The larva actually remains in the bag and carries it along as it feeds.  Only the head and legs will protrude from the developing bag.  You should be able to see these small brownish bags moving, if you look closely.  This process continues until about mid-August, when the larvae mature.  Then they permanently fasten their bags to a branch and prepare to pupate.  
As with many insect pests, control is most effective on young larvae.  If you wait until the bags are attached in August, control will be much more difficult. Several stomach insecticides including carbaryl (Sevin), diazanon, acephate (Orthene), and bifenthrin (Talstar) are also labeled for bagworms (check that label for bagworms and the kind of tree).  Again, these must be used while the larvae are still feeding and moving about in their bags.  The host plant must be drenched to insure that the spray reaches the innermost foliage.  Late June and early July are the best times to apply these chemicals. Waiting until the bags are permanently attached in August, means hand-picking is about the only effective treatment.