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.

Treating Chlorosis with Iron Injections

Posted by: Susan Rose, Tri River Area Extension

Grand Junction – Silver maples really struggle in our area.  I share a story with the Master Gardeners, that it wasn’t until I began volunteering at the Extension office that I learned that silver maples are actually supposed to be green – every one I had seen was yellow, so I thought it was normal for them!

While the best choice is to plant a more appropriate tree to begin with, there are still things we can advise the concerned homeowner.  Getting the watering right can go a long way.  The first challenge is to convince the client where the roots actually are.  Winter watering in this area is an absolute must for these struggling trees, as is avoiding excess water over the summer.  If you really want to guarantee chlorosis, ignore winter watering and run a drip daily in the summer, at the base of the tree!  Yes, we’ve seen this all too often.

A soil nutrient analysis would be very useful in determining what the plant actually needs.  Nitrogen is almost always needed as it gets leached out during irrigation, but in the case of the chlorotic maples we may want to consider the plant’s ability to take up iron as well.  In our high pH environment, the iron in our soils is not very available.

If a soil test confirms the need for additional iron, there are several options: soil applied, foliar, or injections.  Caution should be used and the overall health of the tree should be taken into consideration.  Which brings me to the story I want to share with you.

The tree above was injected with iron directly into the base of the tree.  The tree was under drought stress at the time of the injection.

Iron “burns” in a very distinctive way; the twigs and leaves turn a grayish black.

Note that the rest of the tree is now nicely green!

I don’t think the tree is a complete goner, but it will be a few years before it compensates sufficiently to look good again – by which time I suspect it will again be chlorotic.