The Norman Transcript

June 29, 2013

Iron chlorosis common in OK

Tracey Payton Miller
The Norman Transcript

NORMAN — Iron chlorosis is a problem that afflicts many trees in our state. I’ve talked to countless homeowners and seen numerous plantings around the Metro with this problem. Iron deficiency in the soil is blamed, but it isn’t the root of the problem.

Many think if a tree has iron chlorosis, you must apply iron. This is not an uncommon thought. Iron can be applied by trunk injections, leaf sprays or soil application. This technique will work, but treatments may be short-lived and expensive. Iron applications are only a band-aid for the real problem.

If you ever wondered why red dirt is red, it is typically because of oxidized iron in the soil. Iron is not scarce in our native soils, but it may be more limited in high pH soils. Alkaline soils are those soils over 7.0 on the pH scale.

The real problem is acid-loving trees planted in high pH soils. Alkaline soils are the norm in our area, and these trees are not used to growing in such conditions. What you get are trees that are sickly, lime-green or yellow, easily scorched and unhealthy. Trees may show symptoms in sections of the tree, on one side or all over. Untreated iron chlorosis is unsightly and may lead to plant death, all because certain trees cannot effectively extract the iron needed from our soils.

The best defense against iron chlorosis is simply not planting susceptible trees. We always talk about the “right plant in the right place,” and iron chlorosis is a great example of the wrong plant in the wrong place. Trees renowned for chlorosis include pin oak, water oak, some maples and loblolly pine. These trees may be beautiful in acidic soils and areas of the Deep South, but by and large they suffer here. What a shame.

If you have established trees with these symptoms, there is another option. Lowering soil pH with sulfur can take time, but it targets the cause of the problem. It is best to test your soil before applying any element, especially if it has been more than 5 years since your last test. If you are sure you have iron chlorosis, you may choose a broadcast application of 1-2 pounds sulfur at the dripline of affected trees. I suggest you water trees promptly after treatment to incorporate the product and reduce burning of turf.

This may be done up to twice a year and will help acidify soil. Depending on how high the pH, you may have to apply sulfur over many years. If you have any questions, feel free to call our office at 405-321-4774 or email a Cleveland County Master Gardener at ccmastergardener@yahoo.com.

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