The white fluffy appearing residue might be from one of the many forms of mildew, many of which are called powdery mildew. Most are prolifc in conditions of warm weather and high humidity. Or it could be residue from overhead spraying with water or chemicals. We cannot tell for sure. Suggest you take a few clippings to a horticulturist at your local garden center or botanic garden to confirm the problem and the recommended control. Also if the citrus is in full sun for 6-8 hours and receives regular water and fed with a slow release or organic fertilizer formulated for citrus, it should be flowers and fruits. But if it was planted less than three years ago, fruiting trees usually bear sizable crops after three to five years.