CO-Horts Blog

Friday, September 16, 2016

Is your maple looking a little (or maybe very) yellow?

Is your maple looking a little yellow?  It’s possible that it is experiencing an iron deficiency. Red maple and the freeman type maples (of which autumn blaze maple is the most common) as well as red oak and several other species of trees common to our area are all prone to iron deficiencies in alkaline soils (soils with a high pH) like those common to Colorado’s Front Range.    

Posted by: Eric Hammond, Adams County Extension
        Chloroctic Freeman type maple
These trees struggle to take up iron  (as well as other micronutrients such as zinc and molybdenum) from our soils even though there is normally plenty of iron in the soil.  Under high pH conditions iron tends to be insoluble forms that are more difficult for plants to absorb.  Some plants have evolved mechanisms to overcome this difficulty, however, other species, like the maples listed above, have not. This is likely because they had no need as these species are natives to the eastern portions of the continent where soils generally have a lower pH (in fact sometimes too low) and would gain no great advantage from having evolved specialized and energy intensive iron uptake mechanisms.  Cultural factors may also lead to or worsen the issue by making iron less available or hindering root growth. Such factors include soil compaction and over watering both or which lower soil oxygen levels.

Chlorotic leaves which are beginning to scorch
So how do you know your tree has a deficiency?  Symptoms of iron deficiency are chlorosis (yellowing) of leaves and in severe cases scorching or even premature dropping of leaves.   Iron is not very mobile within a plant so symptoms are worse on the newer leaves. In simple terms the plant uses the iron it has in the first leaves and runs out so the leaves produced later tend to be more chlorotic. Symptoms also tend to get worse as the season goes on, though in really bad or very far along cases plants may be chlorotic even early in the season. If deficiencies are prolonged they will lead to the decline of the tree and eventually its death. 
Freeman type maple in decline due to prolonged micronutrient deficiency 

The best way to deal with this issue is to avoid planting species which are intolerant of our soils.  However, there are several potential treatments.  You can have an arborist inject an iron solution into the trunk of the tree every few years to deal with the issue. However each time you do this you are wounding the tree which creates potential avenues for decay and is generally stressful for the tree.  You can also apply a chelated iron fertilizer.  These products consist of iron bound up in organic molecules which are stable in our soil. Make sure to use products labeled as EDDHA. There are many types and this is type is best for our high pH soils. These are somewhat expensive and need to be applied annually or near annually depending on the severity of the deficiency . Foliar applications of iron are also a possible treatment but they have their own list of drawbacks.  They only green the leaves they are sprayed on so improper application can lead to the tree appearing striped.  They can also stain driveways, sidewalks, patios and other elements of the landscape.  Foliar iron fertilizers will need to be applied annually.  Since it is possible that spring time over watering or issues creating stress for the plant such as soil compaction and girdling roots may be aggravating the issue. Make sure you watch your watering and if possible core aerate around the tree.