Iron chlorosis is a term describing leaf yellowing (lack of chlorophyll) due to insufficient iron. Iron is a mineral essential for plants to make chlorophyll, in turn needed for photosynthesis. Lack of iron in a tree may be due to a high iron need, less effective iron uptake, or insufficient usable iron in the soil. Colorado soils generally have adequate to high iron levels, as evidenced by the many red soils and rock formations. However, Colorado soils are mostly alkaline, causing most of the iron to be in an insoluble form not usable by plants.
Symptoms of iron chlorosis are:
Insufficient soil oxygen or anything that affects root function in the soil can worsen iron chlorosis or cause it to appear in less chlorosis-prone trees. Compacted clay soils and overwatering both result in lowered levels of soil oxygen.
Sometimes, where planting density is high or there is turfgrass or other under plantings competing for water and minerals, trees may develop iron chlorosis. When plants are overfertilized with phosphorus, iron chlorosis may develop as roots take up phosphorus to the exclusion of iron.
Some locally-used trees that often develop iron chlorosis include maples (red, silver, Amur), oaks (red, swamp white), aspen, apple/crabapple, peach and some pines. It is best to avoid planting these species where soil pH is greater than 7.5.
There are several treatment approaches:
For more information, see the following Colorado State Extension fact sheet(s).
For more information, see the following Planttalk Colorado™ script(s). http://www.ext.colostate.edu/ptlk/2121.html
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