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With fall just around the corner, you may begin to see some physical changes to your trees. While some changes are normal for this time of year, others could signal that your tree is diseased or suffering from pest infestation.
Because signs of distress can sometimes be difficult to tell apart from regular seasonal changes, it’s important to do a physical inspection of your trees before fall starts. This can help you determine whether your trees are healthy or need attention.
Here’s what to look for during your September tree check:
Foliage changes
Fall is the time of the year when the leaves on many varieties of trees turn brilliant shades of orange, red and yellow. People tend to get so excited about the leaves changing color and dropping, however, they don’t often realize that it may be too soon in the season for this to be happening. Some color changes and leaf dropping can be signs of an unhealthy tree.
Normal seasonal changes:
Trees in our region typically start changing colors in early October. The foliage will become patchy through the month and then peak in early November before falling. Depending on where you live on the Peninsula, however, could impact when your trees change: Leaves more inland or in mountain areas may start changing a week earlier than those in other parts of the region.
Some trees common to our region that change color in the fall include the valley oak (yellow-orange, brown), Japanese maple (red, orange, yellow), ginkgo (yellow), bigleaf maple (yellow) and western sycamore (yellow, orange).
Signs of stress:
If you notice premature leaf drop (before November), it could indicate stress from drought, disease or pest infestation. These signs warrant a closer inspection and potential treatment. Discolored or wilting leaves that are yellowing or browning – despite sufficient water – also may suggest problems, including root issues, nutrient deficiencies or insect damage.
If your tree’s leaves are curling, it could have aphids. These small insects attack maples, oaks, elms, crape myrtles and fruit trees. They secrete sticky honeydew, leading to sooty mold and damaged leaves. Scale insects can make leaves turn yellow. They target oaks, maples, magnolias, citrus, and ornamental shrubs, appearing as small bumps on bark and leaves. They cause yellowing and wilting by sapping nutrients.
Oak moth caterpillars can strip oaks of their leaves, leaving only bare branches. Their droppings appear as black pellets under the tree, and they may create webbing as they move. These caterpillars are most active from summer into the fall.
Bark peeling
Bark peeling can be normal for some trees, but it also can be a sign of distress.
Normal seasonal changes:
Trees can shed their bark (or exfoliate) at different times of the year depending on the species. In our region, for example, eucalyptus and madrone trees shed their bark in the summer months. This is a natural part of growth and survival strategy for some species and can be more noticeable during Autumn after a tree’s leaves fall off, exposing the bark.
There are also other reasons why a tree’s bark might fall off that could signal distress or disease.
Signs of stress:
Cracks or splits in the bark can be caused by sudden changes in temperature or water stress, leaving the tree vulnerable to further damage. If fungal growth is spotted at the base of the tree or on the trunk, this can indicate internal decay or root rot, which can be fatal if not addressed.
Insects also can damage bark. Borers, a group of insects that tunnel beneath bark, can create large holes in wood or cut a ring into the bark around the trunk. Their activity can damage a tree’s ability to transport water and eventually lead to its death. Sawdust-like frass at the base of the tree, also can signal the infestation borers, as well as aphids.
Branch dieback
All trees will have some dead branches as a natural part of their lifecycle, but too many dead branches could indicate that something’s wrong.
Normal changes:
As a tree grows, it puts more energy into its upper canopy, where it receives the most sunlight. Branches that receive less sunlight may die off.
Signs of stress:
Dieback, or the progressive death of a tree’s limbs, generally starts at the tips of the branches. Too many dead or dying branches, especially in the tree’s upper canopy, can be a sign of drought stress, fungi, bacteria, disease or damage from pests. Some insects can attack trees in specific areas, causing damage branch by branch, while others, like borers, can eat part of a tree’s roots, causing limb dieback directly above the root.
Branches can become stressed or die during any time of the year, but it’s especially important to identify and remove them in the fall before the rain comes. Leaving unhealthy branches on your tree could be a hazard: Excessive water could weaken the branches causing them to fall and possibly damage your property.
George Reno is a local arborist at The Davey Tree Expert Company in Menlo Park, which serves communities on the Peninsula, including Menlo Park, Atherton, Palo Alto and Redwood City.
As part of our monthly “Ask your local arborist” column, Reno answers questions from local residents and provides general care and planting tips. If you have a tree-related question, email lifestyle@embarcaderomedia.com or post in the comments section at the end of this column.
