Overfertilizing plants can lead to a build up of mineral salts in the soil that are damaging to the plants and soil microbes. These salts have a drying out effect that can also kill plants and microbes.
Plant fertilizer is a combination of mineral salts used by plants for growth. A small amount of fertilizer given to plants encourages a spurt of new growth and larger fruits. However, too much fertilizer can harm plants and the microbes living in garden soil. The effect is called "fertilizer burn," and it causes the roots of the plant to dry out. The damage to the roots causes the top of the plant to turn yellow or brown or even die. The destruction of soil microbes may also cause problems for the plant because many microbes are beneficial for plants.
It may be possible to negate the effects of overfertilizing plants as long as the effects of yellowing plant leaves are caught early. Start by preventing the addition of fertilizer and removing any granular fertilizer still present around the plant. Dilute fertilizers in the soil by watering the ground until it is completely soaked. Continue to water the ground every day for a week. This should remove most of the fertilizers that are burning the plant. The best thing to do after this is wait and see if the plant recovers.