Boulder County Tree Care

Check for changes in the leaves of the tree, such as early fall coloration,
chlorosis, or scorched edges. (Photo: Shutterstock).

Carol O'Meara, Colorado State University Extension

Carol O’Meara, Colorado State University Extension

BOULDER COUNTY – Trees this summer have dealt with many challenges, from wet feet to intense heat, and some are starting to throw in the towel. Although the temperature continues to bake us, symptoms of stress on our trees from a summer of strange weather are showing up all over town. Help your trees go into fall with a late summer tree inspection.

“We do a tree survey every summer; it’s how we’ve picked up on problems,” said Kathleen Alexander, City of Boulder Forester. “It’s a (health) checkup. Trees need routine maintenance like pruning or pest control.” Alexander shared pointers for giving your tree a checkup yourself:

– Is there anything different or unusual about the tree? Stand back so that you can see the tree from top to bottom. Does the canopy look full all the way around, and is it the same as in previous years?

– Check for broken branches that might not have been obvious earlier in the year. “If the tree has a hanger (a partially broken branch dangling within the canopy) you might not see it until the leaves on it turn brown. Then you look up and see the branch is cracked,” she said. Large, broken limbs are hazardous, so contact an arborist to have them remove it.

– Is the crown thinner; can you suddenly see daylight through it? Loss of leaves could be due to stress on the tree or from frost early in the year that prevented the tree from having a full set of leaves. A third reason is mid-summer leaf drop.

Mid-summer leaf drop is characterized by trees leafing out normally in spring, then dropping leaves in late July or August for seemingly no reason. When trees lose a lot of fine roots during dry winter, they can’t support summer’s lush canopies. Leaf tips brown and leaves drop from the tree.

– Check for changes in the leaves of the tree, such as early fall coloration, chlorosis, or scorched edges. Scorched leaves show up as evenly discolored areas on leaves that are dry and slightly curled, moving from the tips inward. These brown areas have no colored rings, called halos, or fruiting bodies of fungus on them.

Compounding the mystery of leaf problems this year is the cool wet weather followed by heat, then cool moist weather followed by more heat. Leaf spot diseases, such as Marssonina or Septoria thrive in the type of weather we had. Infection spread during the cooler weather and symptoms are showing up now.

Fruiting bodies of fungi usually show on the leaf as small, pimple-like speckles and often have red or yellow halos around the diseased area. Bacterial disease on leaves will have this halo as well, along with a slimy or greasy looking center spot. If your tree develops these ‘leaf zits’, you should suspect a fungal or bacterial disease.

Many people notice the odd bright yellow discoloration of trees in our area caused by iron chlorosis. Although iron is contained in our soils, our high pH makes it unavailable to plants. They suffer by being unable to make chlorophyll, the green coloration in leaves. As a result, we have a landscape of trees that are a flaming lime-yellow in color.

In most cases leaves become pale yellow but veins remain green. Iron chlorosis can contribute to the death of the tree by reducing the chlorophyll to the extent that leaves develop brown spots between veins and die off, or leaves are stunted and branches die back over winter. Helping trees overcome their iron chlorosis through applications of chelated iron is a life-long commitment, one that must be addressed several times each season, year after year.

By Carol O’Meara, Colorado State University Extension. Colorado State University Extension, together with Boulder County Parks and Open Space, provides unbiased, research-based information about consumer and family issues, horticulture, natural resources, agriculture and 4-H youth development. For more information contact Extension at the Boulder County Fairgrounds, 9595 Nelson Rd., Box B, Longmont, 303.678.6238, e-mail [email protected] or visit