Hello Laurie,

Autumn Blaze Maple does suffer some from iron chlorosis. During our research for your questions we found a similar question which was answered by our resident tree expert from CSU, Dr. Alison O'Connor. We have also included 2 CSU documents:  1) CMG Garden Notes #1733: Iron Chlorosis of Woody Plants and 2) Fall & Winter Watering #7.211.

Dr O'Connor's response: Sadly, many maples suffer from our soils that are high in pH (not necessarily because our soils are clay). A pH above 7.0 leads to a general unavailability in iron because the iron converts into a form unavailable to plants. Our soils tend to have a lot of iron, but the high pH restricts the uptake of iron by the plant.

You can do a couple different things to treat your Autumn Blaze maple suffering from chlorosis:

1. You can apply a foliar spray of iron to the leaves. This is a one-year treatment, but is inexpensive. If done well, I've heard from people that it may last for two seasons. You can use any chelated iron product (like EDTA) and you would mix the iron in a sprayer and spray the foliage. This would be done after the trees have leafed out (doing it now wouldn't be advised, since we're towards the end of the season).

2. You can do trunk injections of iron. While this is effective, I hesitate to recommend this, as someone will bore (small) holes into the base of the trunk, which does cause a wound. I don't like adding wounds/stress to our trees which tend to be already stressed from our environment. But this is an option and should be done by a certified arborist--there are a few in the area that do these treatments. They may apply the iron sulfate you've mentioned, but I've seen trees lose their leaves as a result of the injection. A better product would be to use an iron chelate with EDDHA or EDMA. This treatment can last two seasons.

3. The third option is to apply iron chelate (again EDDHA or EDMA) to the area at the base of the tree by mixing the iron in a bucket and pouring it at the base. You will need to pull back any mulch and/or remove any turf growing near the trunk. Timing for this would be as the leaves are emerging in spring, BUT there has to be good water uptake, so make sure the tree is well watered. This may last two growing seasons.

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To answer your questions about Liquid Chelated Iron with EDDHA, a quick Google search shows that such products exist as well as a water soluble product. Dr. O'Connor's response addressed when to apply such treatments.

Removing the sod from around the tree is not necessary unless you will be adding a liquid chelated iron to it which will need to be poured around the base of the tree (Dr. O'Connor mentioned this in her reply). Rototilling is not recommended as it is too damaging to surface roots. Mulch is fine as long it is 6" away from the base of the tree. Neither compost or topsoil are recommended.

https://cmg.extension.colostate.edu/Gardennotes/223.pdf

https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/

It you have additional questions please do not hesitate to contact us. 

Sincerely,

Becky C. and Anne C.