Since we are not sure what is wrong, we grab a bag of fertilizer and throw a couple handfuls around the afflicted plant. Now stop your whining and get better. For some reason, we have the erroneous idea that giving a plant extra fertilizer should cure any ailment. Fertilizer is not a magical medicine that can heal all plant problems. In reality, it is not a curative at all, but simply a source of nutrients for their survival.
Fertilizer only helps fix problems when the plant is deficient in a certain nutrient.
Most plant ailments are not caused by a lack of nutrients, but because of incorrect watering or an attack by insects or diseases. Even iron chlorosis, which is an iron deficiency, is normally a symptom of over-watering. Once the watering is reduced, the plant often recovers. Most sickly plants do not need an extra dose of fertilizer, which only stimulates new growth. Actually, this can do more harm than good.