Chlorosis is starting to rear it’s ugly head on a number of plants in the Midwest. Chlorosis is a yellowing of the leaf due to low levels of chlorophyll (the green pigment in leaves). It starts by leaf tissue appearing paler green; however the veins of the leaf stay green. Leaf tissue progressively turns yellow, and may turn white in advanced cases. Leaf margins may develop a scorched look with symmetrical brown spots between veins. Trees that commonly show chlorosis include:
Pin, Red and White oak ~ Quercus varieties
Red and silver maples ~ Acer rubra or Acer saccharinum
River birch ~ Betula nigra
Tulip-tree ~ Liriodendron tulipifera
Sweet gum ~ Liquidambar styraciflua
Bald cypress ~ Taxodium distichum
White pine ~ Pinus strobes
There are many causes of chlorosis. The most common cause of chlorosis in the Midwest is due to iron and manganese deficiencies resulting from alkaline soils. High soil pH causes iron and manganese that is present in the soil to become unavailable to the plant.
Where soils are alkaline, avoid planting trees that do not tolerate alkaline soils. For existing trees, fertilize soil with a nitrogen and sulfur-based fertilizer from early spring through mid-May, use chelated iron which is not affected by soil pH (this is best used in spring), or have the tree injected with iron or manganese.
Anything that negatively impacts the root system (physical damage, flooded soils and dry soils) can also lead to chlorosis. The abundant rains this year are starting to affect the ability of roots to take up nutrients, so a treatment of iron to the soil may not work in all cases. The best management practices is in dry seasons, be sure to provide enough moisture to plants and when the season is wet, there is not much to do but wait for drier weather.
© Ilex ~ Midwestern Plant Girl