i live in Colorado. What's the problem with our Autumn Blaze maple tree? Its leaves have turned yellow, and about half of the leaves have black spots and are dying.
Autumn Blaze is a hybrid of red and silver maple. Red maple (Acer rubrum) and silver maple (Acer saccharinum) are both prone to developing problems when grown in alkaline clay soils, which we have in Colorado.
Plants need iron and manganese to make chlorophyll, the photosynthetically active green pigment in leaves. In alkaline soils, iron and manganese are in a form that is less available to plants. Many maples have either a higher need for iron/manganese or are less efficient at taking it up from soils. Less iron/manganese means less chlorophyll.
Affected leaves are the newest, youngest ones; they turn yellow but veins remain green. When leaf cells are very low in chlorophyll, they scorch due to lack of that protective pigment and may die. When advanced, chlorosis becomes blotches of dead cells that look brown/black on leaves.
Autumn Blaze looked promising when it was first released and sold in nurseries, but many are now reaching an age and size where they, like their parents, could be expected to develop chlorosis. You can try adding iron and manganese chelates to the soil. Reducing soil pH to make it less alkaline is not very feasible. Iron sprays on leaves can green up leaves, but sprays can stain brick or concrete and become increasingly difficult to apply as the tree grows. Iron sulfate or manganese sulfate mixed into soils may help temporarily. Tree services could inject or implant iron in the trunk, but drilling holes for implants is itself potentially harmful to the tree.