What is Chlorosis?
Chlorosis is a serious tree ailment where a tree has lost the capacity to make enough chlorophyll. Without enough chlorophyll, the tree cannot make the energy it needs to live and grow.
Causes of Chlorosis
The scientific community and industry of arboriculture most frequently implicate soil pH as the reason for chlorosis. High soil pH ties up iron and makes it far less available to a tree. While valid, this may not be a complete picture because some trees that grow in high pH soils do not display chlorosis symptoms. There may be other factors.
Another Potential Cause of Chlorosis
Root loss or an unhealthy root system may also contribute to symptoms of chlorosis. Gary Watson from the Morton Arboretum reported improvements
in the color of chlorotic trees in response to soil-applied paclobutrazol.
While not a complete remission of symptoms, the color of chlorotic
trees improved without the addition of mineral elements or alteration
of soil pH. The color improvement was attributed to a threefold increase in fibrous
roots. Could it be that a more vigorous root system is capable
of extracting iron even from soils with higher pH? It appears
from this work that this is the case.
Treating Chlorosis
Successful treatment of chlorosis involves a multifaceted approach.
- Determine if the soil is compacted. Soil Compaction will inhibit root growth by preventing roots from moving through the soil. It will also dramatically slow oxygen and water exchange, both which are needed for healthy roots to grow.
See treating soil compaction.
- Apply Cambistat to the tree. This will redirect energy from crown growth and stimulate the roots to grow. However, since these trees are growing very little, Cambistat by itself could take a while to work. If the tree is very weak, results with Cambistat alone could be poor.
- Give an immediate increase in chlorophyll by macro - infusing an iron containing product called Verger. This must be done in the fall of the year, usually within a few weeks before dormancy. This advanced treatment will turn the leaves green for 3 years.
Do Not Fertilize Chlorotic
Trees with Nitrogen
Nitrogen makes trees
bigger. This will compound the tree’s problem in two important
ways. The forced growth caused by adding nitrogen will further
reduce the energy supply in the tree. The second problem is that
a larger tree has a greater need for iron – further increasing
chlorosis. Responsible fertilization will first involve taking
a soil test to determine what elements are missing, and then these
elements can be added to the soil for the tree to utilize as its
roots grow back.
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