Iron chlorosis

What it is

A nutrient problem: iron the tree cannot absorb in alkaline soil

Trees affected

Silver and red maple, Freeman maple, certain oaks, Scotch pine, birch and others

Where in our area

Valley soils and any high-pH ground, about 4,000 to 6,500 feet

Key sign

Yellow leaves with green veins, newest leaves first

Link

Often paired with drought, wet soil or root problems

Our soils are alkaline, so chlorosis is one of the commonest leaf complaints on maples, oaks, pines and many ornamentals. Colorado State says the iron is in the soil but is locked in a form roots cannot absorb. Soil and nutrient correction is outside what we do. This page covers what to look for, which trees, what an arborist checks and when pruning or removal is the answer.

What does iron chlorosis look like?

Leaves turn yellow while the veins stay green. The newest leaves at the branch tips show it first, and in severe cases every leaf is affected, with scorched brown patches in the worst spots, as Colorado State describes.

Because other nutrient problems can look alike, and because root damage and overwatering can cause the same pattern, a diagnosis from a photograph is a guess. The arborist reads the whole tree.

• Yellow leaf tissue with green veins
• Newest leaves worst
• Brown scorched patches in severe cases
• Small leaves and short twigs

Which trees and which elevations?

Colorado State names silver maple, red maple and certain oaks as plants with a high iron requirement. Utah State University rates Freeman maple low for alkalinity tolerance and warns of chlorosis in high-pH soil, and reports Scotch pine needles yellowing on the most alkaline soils. In our area those are silver maple, Freeman maple, Scotch pine and oaks.

Soil pH is a property of the ground, not the elevation. Valley soils on the Truckee Meadows and Carson Valley floors are the usual setting; Colorado State says the usual cause is alkaline soil, and alkaline irrigation water can make it worse.

Why does it happen, and what else looks like it?

The CSU PlantTalk note says iron is plentiful but alkaline soil holds it in a form roots cannot absorb. Overly wet or dry soil adds to the problem. Chlorosis rarely kills a tree outright, but it weakens it, and weak trees draw pests such as the borers on our bronze birch borer page.

Several other causes mimic it: drought scorch, root injury, overwatering and the tree's age. See drought stress and dieback.

What does an arborist check?

The arborist checks the pattern of yellowing on the crown, whether the tree is a species prone to it, the soil and drainage around the trunk, the roots and root flare, and whether branches are dying back.

• Species and its known tolerance
• Pattern and extent of yellowing
• Dieback of twigs and branches
• Root flare, soil and drainage
• Irrigation and lawn conditions

When is pruning or removal the answer?

Chlorosis alone is not a reason to prune or remove. Dead twigs and branches that follow years of chlorosis can be cut out. Heavy pruning of a stressed tree is rarely wise.

Removal is the answer when the crown has lost most of its live wood, when decay is in the trunk or base, or when a tree that was already weak has split. For many silver and Freeman maples with long-term chlorosis, the trend over several years tells the story.

What does Battle Born Tree Service do about chlorosis?

We look at the whole tree, not only the part that worries you, and the free estimate lays out pruning, watching the tree or removal. The crew is eight people, two of them ISA Certified Arborists, and the phone line is staffed seven days a week at 775.232.8243. We identify the problem, prune out dead or hazardous wood and remove trees that cannot be saved; we do not spray, inject, fertilize or apply products.