Question
i live in st johns, newfoundland,canada.i have big mature maple tree,s and have a big problem with span worms.eating away on the leaves.some people say there,s a plug you can get to put in the tree,s.or is there anything i can get.please help.

Answer
I would not recommend the injection system for this insect. And i am not sure it is legal in Canada. Insecticide sprays work--Bt works if sprayed on the new leaves and before the insect get too large (the caterpillar has to eat the Bt so you will get some defoliation before the insect is killed. Contact insecticides work when sprayed on the leaves. Sevin works and you will see the results almost at once.
Here is a web link to information from that area you might want to contact the local entomologist and see what they are recommending.

  http://www.carleton.ca/catalyst/e4.html