Black Bugs on Needle Trees Near Vegetable Garden

I'm wondering if you can tell me of some plants that can be used for pest management. I am growing a modest garden with carrots, onions, tomatoes and spinach, as well as several herbs. I know that often marigolds can be used to help keep certain bugs away, but are there others? I am hoping to keep my garden organic, and it is very close to some fir/spruce trees in my yard that tend to get alot of bugs (don't know what they are) but assume that they will eventually get in the garden. These bugs are black, about 3-4 millimeters and leave little shiny sticky strings in the trees. One year we sprayed for them, but others we have just left them and I think they have just gone away....suspect they'll be back!!

From your description it is very hard to guess what these bugs might be. The strings makes me think of caterpillars that would start out tiny and black and disperse on the trees when they get bigger. But if they always start on the trees they are not likely to attack your vegetables. Most caterpillars are quite host specific. But I am sure they are not doing the trees any good and a spray early in the year with pyrethrum soap spray and then innoculating the soil with Scanmask (a beneficial nematode) in the fall would control their numbers.
The book "Organic Pest & Disease Control" by Barbara Ellis (Richters catalogue #B6710) would be a good book to use for ideas on companion planting and other topics for a healthy garden.