Over fertilization could well be the problem, and probably is.. However, much depends on the amount of fertilizer you apply with each application.. For a young in ground citrus tree do not use a fertilizer with higher than an 8-8-8 analysis during the first 3 years of the trees life. A 1 year old tree should be fertilized 6 times per the growing season equally spaced out. A 2 year old tree 5 times the growing season equally spaced out. A 3 year old tree 4 times during the growing season, For trees 4 years and older fertilize 3 times the growing season. For young trees apply fertilizer in a 3-ft. diameter circle around the tree. As the tree becomes older, the area fertilized should be enlarged as the root system expands. As a rule of thumb, fertilize an area twice the diameter of the tree canopy. Care should be taken to avoid root and trunk damage by uneven placement or mounding the fertilizer against the trunk. Recommendations for the amount of fertilizer to apply. Apply 0.3, 0.6, and 0.9 lbs. actual nitrogen per tree during years 1, 2 and 3 respectively (divided the recommended actual nitrogen by the number of applications per growing season). Thereafter, increase the amount of actual nitrogen applied according to tree growth, up to but not more than 1.5 lbs. actual nitrogen per tree per year.