Written by: Board Certified Master Arborist WI-0556B Fred Hoppe and Certified Arborist WI-0477A August Hoppe
When trees that normally have dark green leaves start to turn pale and yellow, trouble lays ahead for the tree. This yellowing of leaves is a likely indicator of chlorosis. Chlorosis is a condition where the tree is unable to efficiently produce chlorophyll. Chlorophyll is a vital leaf component which is responsible for energy absorption for trees. Trees without enough chlorophyll will not be able to grow and thrive.
Common causes of chlorosis include nutrient deficiencies related to soil alkalinity (high pH), drought/heat stress, poor drainage, or soil disturbance such as compaction. Iron and manganese are the common micro-nutrient deficiencies that cause chlorosis in trees. These minerals are often not lacking in the soil, rather a condition exists where the tree’s root system is unable to obtain them in usable forms. Poor absorption of micronutrients is common in Wisconsin because of the high pH (alkalinity) of many soils (pH greater than 6.5).
Our slightly alkaline soils and summer heat with periods of drought can trigger chlorosis in some of our most popular Milwaukee area trees. Chlorotic prone trees include red maples, silver maples, oak trees, birch, magnolia and white pine trees.
Chlorosis is a progressive disorder that starts off as paler leaves that eventually become brighter yellow. This worsens over time (usually a period of years) and leaves start to curl at the edges of the leaves and eventually fall off. If left unchecked, chlorosis often can kill trees.
There are several treatment methods to combat chlorosis in trees. It starts with an inspection by one of our Certified Arborists to determine the cause and severity of the chlorosis. Some treatments are designed as short-term fixes to deliver the needed micronutrients, while other treatments are performed to increase overall root health in the tree. Often multiple treatments are performed in conjunction with one another.
Soil Fertilization: Hoppe Tree Service has a specific fertilizer blend used with chlorotic trees that contains acidifying agents, soil conditioners, and essential micronutrients. This treatment helps lower the pH level of the soil and delivers the needed nutrients.
Trunk Injection: Trunk injections with an iron solution can be done in one year or three year dosages. One year dosages of iron can be done anytime of year while the three year dosage are performed in the fall to be done in fall.
Growth Regulator: Trees treated with paclobutrazol, which is an active ingredient, show an increased production of fibrous roots. This helps the plants by expanding the area of soil the plants can pull water, minerals, and other resources from. This treatment is applied to soil and may be applied anytime that this ground is not frozen or saturated with water.
Soil Remediation: The primary goal is to create a suitable soil environment that promotes fibrous root growth resulting in greater capacity to acquire water and nutrients from urban soils and a healthy more vigorous tree. Compressed air is used to reduce soil compaction, increase oxygen in the soil, and incorporate organic matter into existing soils. This treatment increases the likelihood of improving the soil structure and establishing a beneficial for tree root growth.