For the past few years my apricot tree in Santa Barbara has been struggling against an attack from the vile oak root fungus. Oak root is a soil borne fungus that attacks the tree from the the ground up and the inside out. It spreads under the bark layer and eventually girdles the tree - preventing the tree from taking up water and nutrients - which kills it.
For the past couple of years we've experimented with worm composting of kitchen waste and we also compost yard waste. I've been applying lots of compost to the soil around the apricot and I even applied worm tea directly onto the bark at the trunk. Worms break down organic material into tiny particles that are easy for plants to absorb. And you can, um, smell the biological activity.
There's theory (and anecdotal evidence) that applying active fungus and bacterial agents can help a tree fight disease. Fairview Gardens in Goleta actually applied a soil/manure paste to their avocado tree trunks in attempt to strengthen the health of their trees.
The idea is that certain live elements in soil produce natural anti-biotics that fight infections. (penicillin comes from naturally occurring anti-biotic fungus). And whether or not I produced the results by applying pro-biotics, the tree has not died and is in fact re-growing bark to cover the area of infection and lost tissue.
To strengthen the roots and help the tree fight back, I pruned the tree back, cut all the dead wood out and thinned this years apricot crop by more than half.
Then I gave the tree a serious booster shot of nutrition. I found a useful organic fertilizer recipe in the June/July 2006 issue of Mother Earth News. I mixed and applied the fertilizer, then covered it with about a 1 inch layer of finished yard compost - just a few inches back from the trunk and out to the drip line. I watered it down and now hope that I've given the tree a quick hit of nitrogen along with a slow release of nutrients, trace minerals and organic material, combined with the living mulch of native plants that cover the ground under the tree.
Follow the link to Mother Earth News for the fertilizer recipe and the directions for use.
BTW - you'll find that buying the ingredients in small quantities by the box at your local garden center is REALLY EXPENSIVE! If you're serious about greening up your yard and garden either find an online supplier who will ship in bulk bags or visit a garden/farm center that sells in bulk.
In Santa Barbara/Goleta that is Island Seed and Feed. Buying measured quantities from the bulk bins cost less than half what it cost to buy small packaged quantities at another nursery nearby. Plus they had additional cool stuff to mix in like phosphate rock, green sand, blood meal and gypsum! (One other tip - for fast green-up and to energize the soil quickly, I substituted 1 part blood meal in exchange for one part seed meal.)