Spraying large trees is not practical. Use trunk implants of soluble iron sources on trees. The plastic capsules are inserted into holes drilled in the trunks. As the trees grow, they cover the capsules. The disadvantage of this method is the necessity of drilling the holes in the tree trunk to make the implants.
Trees vary in their ability to tolerate repeated wounding.
Drilling a series of holes in the trunk every two to three years may become a more serious problem than the deficiency. Keep trees with implants well watered and fertilized so they heal as quickly as possible. Adding fertilizer that contains iron to a soil that is not sufficiently acid will not help. The plants roots will not absorb the additional iron until the soil is made more acid. Visuals associated with this text.