Iron chlorosis treatment

There’s iron in your soil. At pH 8, the roots can’t absorb it.

Utah soils are typical of dry climates everywhere: full of lime, and alkaline, with a pH generally somewhere between 7.2 and 8.3. At that pH, iron reacts into solid forms that roots simply can’t absorb. So this is rarely a shortage of iron. It’s iron the tree is locked out of.

Iron is needed to make chlorophyll, the green pigment that runs photosynthesis. Starve a tree of iron and the leaf loses its color. But the veins, which get first call on what little arrives, stay green. That yellow leaf with a dark green vein network is called interveinal chlorosis, and it’s close to diagnostic.

It gets worse through the season. The first leaves may come out normal size with a little yellowing; later leaves emerge smaller and much paler. It can show on a single branch, on half the tree, or on all of it. Left to recur year after year, it thins the canopy, causes dieback, and can eventually kill the tree.

In Utah the regulars are silver maple, red maple, red oak, river birch, tuliptree, sweetgum, flowering pear and flowering plum, though the list isn’t closed.

Yellow leaves aren’t always chlorosis

Worth saying it plainly, because we get calls about it all the time. Overwatering, herbicide drift from somebody’s lawn treatment, girdling roots and other deficiencies all turn leaves yellow, and every one of them needs a different answer, sometimes no treatment at all.

The pattern on the leaf is what separates them. Chlorosis leaves the veins dark green against a pale leaf, because the veins get first call on what little iron arrives. That’s close to diagnostic, and it’s the reason we look before we quote.

A trunk injection can hold a badly affected tree for two years

Liquid soil drench. Iron is mixed with fertilizer and applied around the root zone. The critical detail is which form of iron: most chelates fall apart at high pH and do nothing in our soil. The one that holds up in alkaline ground is FeEDDHA, and using the right chelate is the difference between a treatment and an expensive watering. Best applied in spring, though it can go on later if symptoms return. Other micronutrients can go in at the same time.

Trunk injection. Iron is delivered straight into the tree’s vascular system through small ports in the trunk, bypassing the soil chemistry entirely. It’s more involved than a drench and it does wound the tree slightly, so we don’t reach for it first. On a badly affected tree, though, it’s far more reliable, and a single treatment can hold for up to two years. We use a macro infusion system for this. It carries a higher volume than the micro injection we use for borers, because iron and fertilizer go in as a larger dose through ports in the trunk.

Foliar sprays are the third option, and we mention them mainly to set expectations: they green a tree up quickly and incompletely, and they don’t last. Soil and trunk treatments are what actually fix the season.

Iron rarely travels alone. When we’re already treating the root zone, a full macronutrient and micronutrient correction usually goes in at the same visit. See tree fertilization & soil health.