Take steps now to prevent chlorosis from permanently damaging maple trees

Be on the lookout for chlorosis problems in your maple trees.

Last year in mid-July a reader inquiry prompted me to look into an abundance of maple trees with yellow leaves. Careful inspection of some leaf samples showed green veins in the yellow leaf indicating that the trees were suffering from iron chlorosis. With the article explaining the problem I submitted a photo of a neighbor's tree, which was a good example of the problem. This spring I inspected the same tree and it is already showing the signs of the second season with the iron deficiency. The leaves are yellow as they were last year, but this year they are a little thin and smaller than normal. At the top you can see a few bare twigs, which are not going to develop leaves.

Iron is essential for all plants in the photosynthesis process. Iron enables the plant to produce chlorophyll (the green in the leaves). The green leaves convert sunlight to food for the plants. Some plants like pin oaks are widely known for chlorosis problems, but any plant is susceptible if adequate soluble iron is unavailable. Iron is a common component in the soil. It becomes insoluble when the soil pH reaches 8. In the hilly loess soil (fine light brown silt) part of Sioux City the pH is typically 7.5.

Since this is a localized effect and plants vary in sensitivity the result is scattered yellow trees. Localized change in pH is fairly common. Frequently it is related to construction activity where mortar or concrete scraps become mixed with the soil. A neighbor had a problem with one maple after adding a room to the house. I had a walnut tree develop chlorosis with no identifiable changes in its environment.

If you have a tree that was yellow last year you should inspect it now. Second year symptoms described above suggest that you did not take action last year or your treatment was ineffective. In either case you should be taking corrective action now so the tree has a full growing season to recover from the food deficiency. The bottom line is what to do next. In the short run the tree will not be permanently damaged. It is the same as you going on a severe diet for a while. If the condition persists the tree is weakened and will ultimately die. In my neighbor's case the first year it was just yellow. The next year a few leaves at the top were withered and brown. The third year about the top half was withered, and then he removed the tree.

Materials to treat chlorosis are readily available at a professional garden store. The seasonal garden departments will not be much help. Treatment is available as a quick fix foliar spray, as a trunk spike containing iron chelate, or as a pellet fertilizer containing ammonium sulfate and iron sulfate. The pellet material is applied by drilling holes around the drip line and pouring a small amount in each hole. For large trees the pellet material is the most effective.

A spray treatment would be all right for a small, newly planted tree.

Several options are available for making holes. A water powered root feeder will do. Earth augers that drill a 1 1/2- to 2-inch hole can be obtained at the garden store. These are powered with an electric drill. You can also make a very effective driller by assembling some short sections of iron pipe into a T and attaching a hose connection to the T. Attach the pipe to your garden hose and let the water pressure do the drilling. Space the holes about 3feet apart around the perimeter of the drip line. A 6-ounce juice can is a good measure. Use one half to a full can per hole depending on the tree size. The measure is not real critical as it will be gradually dissolved and absorbed by the tree.

I ran across a new iron deficiency product this year called Ironite. It comes in a 40 pound bag and is intended for application with your fertilizer spreader. The iron and nitrogen content is lower than the ammonium sulfate/iron sulfate product so it would probably not be as effective for a quick boost to a problem tree. It would have some merit for easy application to a large area.

For further questions contact the Woodbury County Extension Service, 712-276-2157.