Before you fertilize or consider treatments for microelement problems, have a soil test done. Your tree may require soil acidification before fertilization, or treatment of microelement problems. Fertilizers add elements essential for healthy growth. Trees get their energy from the sun. Leaves and needles trap energy in a molecule of sugar.
Sugar is tree food.
Keep leaves and needles healthy by timely treatments so trees can get their food. Keep soils free of compaction so roots can get water and essential elements. Do not over fertilize. Some insects and microorganisms DO start tree problems. When in doubt about what to do, contact the extension agents from your county, state, or university, or ask the United States Forest Service or professional arborists.