Medicap FE FE12X5 Systemic Iron Tree Implant, Pack of 5 Systemic iron tree implants Trees most susceptible to iron deficiencies are pin oak, black locust, birch, pines, magnolia, dogwood, peach, pear, apple, etc Useful in trees where iron deficiencies are difficult to control by foliage or soil feeding 3/8-inch diameter implant 3/8-inch diameter implant