In the past couple of weeks some of our large shade trees have signs of chlorosis showing up. The leaves are not the medium and deep green they are normally and can have darker veins that fade out into the surrounding leaf tissue.

Chlorosis is most of often caused by a nutrient deficiency, not because there is enough of resources in the soil, but the plants inability to take up the nutrients. The chlorophyll cells in the leaf tissue require Iron (Fe) or Manganese (Mn) in order to create the green color we see and much more importantly create energy for the trees for current and future growth.

There are some "regulars" that show chlorosis almost every year. Pin Oaks, while no longer strongly promoted in the trade for this very condition is a good example. There are lots of Pin Oaks in the landscape so we see this quite commonly. We often see chlorosis affecting maple (especially red, silver and hybrids) and birch trees in the landscape.

In the spring it is not uncommon to see Birch trees with yellow or yellowing leaves early in the spring, especially we have lots of cold wet soils. With those conditions, Birch have difficulty getting either the Iron or Manganese out of the ground. On all the trees, the younger leaves are more impacted than those more established on the plant. Cell development is at a critical stage and without enough Iron and or Manganese leaf development is a challenge for the tree.

There can be various stages of chlorosis on those trees. If it is a minor deficiency, the leaves may just be showing a yellow green color overall with the leaf being entirely intact. Another stage will be the overall leaf showing yellow with the midrib vein and some portion of the secondary veins being deep green. That is as far the available Iron or Manganese could move into the leaf tissue. A third stage is when necrosis (death) of the cell tissue farthest away from the veins begins. The most tender tissue is that around the very edge of the leaf. The second phase of this is the death of tissue between the veins. It starts as a brown speckling look as individual cells or a group of cells dies. The last phase is he death of that leaf.

1. Management of chlorosis could be done in a number of ways according to our University State Specialists. A good place to start is with a soil test if the problem has been on- going for a number of seasons. pH is a big factor, a pH that is too low or high limits availability of numerous nutrients including Iron and Manganese.
2. Correct poor soil drainage and compaction. Avoid saturating soils with excessive irrigation. This can easily happen with irrigation systems that turn on whether water is needed or not.
3. Fertilize with an available form of iron or manganese, using one several techniques. One is spraying small shrubs and trees. This is temporary and a better long term solution should be developed. Chelated iron fertilizers can be worked into the soil in a bed or holes augured into the soil if the tree is in the lawn

Consult with a certified arborist about soil or trunk injection.

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.