If the branches are green when you scratch the trunk I would leave it. I still have new growth coming in on my maple and my magnolia is just starting to get leaves. Everyone told me the magnolia was dead but it is coming. The crappy winter and cold dry spring is screwing with all the plants.

I still have roses sitting there, green canes, and not a single leaf or shoot. This weather is just screwy.

Depending on what type of soil you have, the spikes may not be doing your tree any good. I've been told that in clay soil the spikes are almost useless as they won't dissolve enough to get to your roots.

I'd give it some liquid fertilizer and wait to see what happens. It may surprise you.