Fertilizer burn is a defined as leaf scorch

Leaf scorch

Leaf scorch is defined as browning of plant tissues, including leaf margins and tips, and yellowing or darkening of veins which may lead to eventual wilting and abscission of the leaf...

 resulting from over-fertilization, usually referring to excess nitrogen salts

Fertilizer burn is the result of desiccation of plant tissues due to chemiosmosis

Chemiosmosis

Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration....

, creating a state of hypertonicity.

Treatment

Fertilizer burn can be remedied by soaking the soil with water to flush out excess salts. It can be prevented by applying only dilute or controlled-release fertilizer products.