QUICK TIP: If you have a tree with leaves this yellow, it’s time to make a choice:  treat the tree AND the fundamental problem (soil, past root damage, etc.), OR plan to cut it down.

“Chlorosis” is an abiotic condition characterized by yellow leaves, slow growth, and branch dieback. Chlorosis commonly affects oaks, birch, and maple, although you may see it on nearly any landscape plant.

Signs of chlorosis are mild to severely yellow leaves, usually developing early to mid-summer in the Minneapolis area. Leaf veins remain green while the surrounding interveinal leaf sections are pale green to yellow. Chlorosis is a sign that chlorophyll is not being produced normally in the leaf. Chlorophyll is the substance that allows a plant to manufacture its own food through photosynthesis. Your tree may emerge each spring with rich dark green leaves, then lose color as the season progresses. Yellow leaves can affect the health of your tree in several ways. First, the tree is operating on a negative energy budget when its leaves aren’t making food. Second, the chlorotic leaves are no longer of use to the tree and so it tries to re-foliate, which means it has to use even more energy. Third, chlorosis weakens the tree and leaves it vulnerable to attack by secondary insects or disease. One thing is constant: when a tree’s leaves are yellow, the tree is slowly starving!

Chlorosis can be caused by nitrogen deficiency; however, it is most commonly caused by deficiency or inaccessibility of micronutrients such as iron or manganese. Excesses of phosphorus (P) and/or potassium (K) in the soil may contribute to inaccessibility of nutrients. High pH (higher than 7.0) is also known to contribute to chlorosis. Soils in the Twin Cities Metro area are naturally very high in phosphorus; many soils are also alkaline (pH higher than 7.0). Therefore, fertilizing should not be done on a chlorotic tree without soil analysis.

Chlorosis can also be a sign of insufficient or damaged roots. Disturbance to the critical root zone damages the fibrous or feeder roots. It is these roots that are involved in water and nutrient absorption.

TREATMENT
Successful treatment of a chlorotic tree can be tricky. Because there are many contributing factors to chlorotic leaves, no one treatment is right for every tree on every site. Your arborist will evaluate your situation and recommend a treatment program that suits your needs.