Chlorosis

As you wander through your property you may see maple or oak leaves that are looking kind of yellow.  Yellow leaves are a sign of lack of chlorophyll in the leaves - what arborists call chlorosis. Here in Colorado, chlorosis is a common problem, usually due to the tree’s inability to absorb iron. Other factors can include over or under watering, soil compaction, insects or disease.

Chlorosis is a general term for foliage that is not producing adequate chlorophyll. This leads to a yellow or pale appearance of foliage. The lack of chlorophyll means that the plants most important process is being interrupted. If not corrected chlorosis will lead to dieback of branches and eventually the entire tree. Chlorosis generally is caused by a lack of iron, but may also be caused by a lack in other micronutrients. Iron is present in most Colorado soils, but due to the pH of our clay-rich the trees can’t absorb it.

Identifying Chlorosis

Chlorosis is a major problem with maple and oak trees in Colorado, and other species can also be affected. The signs of chlorosis are any leaves or branches in the tree with inconsistent color. Parts of the tree may appear lime green while other parts are a deeper green. In advanced stages leaves will turn yellow and almost white at times. If you look at a leaf and the veins are darker green but the rest of the leaf is lighter in color - that is chlorosis.

Causes

The main cause of iron deficit is due to pH, as Colorado's clay soil is too alkaline. This causes iron to oxidize in the soil and form insoluble compounds which cannot be absorbed by tree roots. The obvious fix would be just to change the pH of the soil, but due to the buffering capacity of the soil that is near impossible. The clay which makes up most of the soil in Colorado will react quickly with any acid that is introduced and will not result in any change to the soil pH. The only solution to this is to replace or amend all of the soil under your tree, but this is also not feasible in a well established landscape.

Chelated Micronutrients

Since we can’t change the properties of the soil in a timeframe short enough to help trees that are already stressed, the only solution is to give them what they need. Chelated micronutrients are ones that have the metal ions locked up in compounds that stay stable in the soil. There are many different chelates for each micronutrient and their stability in soil varies greatly. Using the wrong chelated fertilizer will not be effective, because if it is not stable in the soil it will just react and wash away.

Getting Technical Here - Leibig's Law of The Minimum

Plamt growth will be limited by the micronutrient that is most deficient. This means that even if a deficient micronutrient is added plant health will only be improved to the point that another micronutrient becomes the limiting factor. This is important with chlorosis because even though the iron may be available, if there is not enough available manganese the tree may not fully green up. For this reason it is advisable to supplement soil with all micronutrients that are less available in alkaline soils. The nutrients we advise you use are

·       Iron (Fe) EDDHA

·       Manganese (Mn) EDTA

·       Zinc (Zn) EDTA

These can be spread directly onto the soil. You can also add mulch around the tree to reduce competition from grass, and loosen compacted soil. All these steps will help with long term tree care

Trunk Injection

If your tree is severely chlorotic, its best to work with a certified arborist and take swift action. Directly injecting micronutrients is a quick method for getting nutrients into the tree. This requires drilling holes into the tree. Drilling into the tree should be considered a last resort and only for trees that are too far into decline or where adding nutrients to soil has not been effective. This requires specialized equipment and must be done by a tree care professional.