Get to know your trees to keep them healthy

Chicago Tribune

27-04-2025

For a healthier landscape and a greener community, taking care of the trees you have is as important as planting new ones.
'We often think about planting trees around Arbor Day at the end of April, because we know more trees make the world better,' said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. 'But it's just as essential to make sure that the trees we've already got are in good health.'
Large, mature trees are the ones that do good work for us, providing shade, capturing stormwater, handling air pollution, and making our communities more beautiful, safer and more restful. A tree you plant now will take decades to reach a really powerful size, so the trees that are already big are worth our attention, too.
How can you tell whether a tree is in good health? 'Keep an eye on your trees all the time,' Yiesla said. 'Get to know what's normal for them, and watch for things that are different.' Then get expert help to figure out whether the difference is a problem.
'What's normal for one kind of tree may be abnormal for another kind,' she said. The critical question is whether this particular tree looks different from how it did in other years, when you know it was healthy.
Some tree symptoms may be caused by diseases or pests; others may be caused by stress, such as compacted soil, drought or severe weather. 'Sometimes it's nothing. Sometimes something bad is happening,' Yiesla said. 'You won't know until you check it out.'
Look at the tree's canopy of leaves and branches. Does it have fewer leaves than last year? Can you see bare branches at the top?
Inspect individual leaves. Are they normal in size or too small? Are they the same color as usual, or are they too pale or yellowish? Do the veins stand out in a different color of green than the rest of the leaf, indicating that the tree is not producing enough chlorophyll? Are leaves eaten away, leaving only a skeleton of veins?
Watch the blooms. If it is an ornamental tree with conspicuous flowers, such as a magnolia, redbud or horse-chestnut, does it flower the way it normally does? Or are there fewer flowers this season?
Be alert for fall color. An early color change is a sign of stress. 'If you see fall color in July, there's a problem,' Yiesla said. Often in summer, the problem is drought stress, and it's an urgent call to water your trees in hot weather.
Check out the bark. Are there patches of bark falling off? Are there big cracks, bare places or bulges? Are there places where the bark is discolored or feels damp on a dry day? Can you see sap flowing down the bark? Are there fungi growing on the trunk? They can indicate rot inside.
Examine the branches. Look for wounds or places with cracked or peeling bark, especially if these occur in more than one place; they may be a sign of canker diseases. Also, look for swellings and growths around branches. 'These may be harmless insect galls, or they may indicate a serious fungus disease such as black knot,' she said.
Hunt for eggs. Many insects lay their eggs in masses on the bark of trees. Fuzzy beige patches are likely to be spongy moth egg masses. Small light bumps may be spotted on lanternfly eggs. Get any suspected egg masses identified by an expert before you spray with pesticides or take any other action.
To figure out what may be ailing your tree, take clear pictures and submit them to the Plant Clinic (mortonarb.org/plant-clinic) or other experts, such as university extension services. Take closeups of the top and bottom of damaged leaves, and also farther-away photos that show the overall shape and condition of the tree.
The Plant Clinic can also help you identify a tree if you don't know what kind it is. 'Many diseases, pests and stresses only affect certain tree species, or they affect some kinds of trees differently,' Yiesla said. 'You'll be able to take better care of your tree if you know its name.'