Water magnolia trees that are under more stress

This is the time of year to check for magnolia scale, an insect about the size of a pencil eraser. Typically found on the underside of magnolia branches, the scale is responsible for creating an overall thin condition on the tree.

The scale exudes a clear, sticky honeydew after feeding on the plant. Black sooty mold is a fungus that grows on the honeydew. Gardeners often notice the black mold on or under the magnolia before noticing the actual scale.

The mold itself is not the real problem. On small trees, simply pick off the scale and squash them.

Other control measures include spraying with summer-weight oil, or applying an insecticide when the scale is in the active crawler stage, generally in early September.

For trees with a history of magnolia scale, a late winter to early spring application of dormant oil will provide good control for the scale. If your tree is affected, provide extra water during summer to minimize stress.

• Prune shrubs that put on a lot of growth this year. Prune them as needed to keep them in the proper scale for your garden.

Growth will be mostly hardened off in early July so there should be minimal new growth when pruned at this time.

Try using a pair of hand pruners instead of an electric hedge clipper to create a more natural look by making individual cuts at different heights throughout the shrubs.

For a more formal look, make cuts at the same height. Prune right above the leaves to help hide the cuts. Careful pruning will leave the plants smaller but not looking "sheared."

Remove dead wood as necessary.

• Some varieties of crabapple are very susceptible to a fungal disease called apple scab, and those not treated in spring may be losing their leaves at this time. The weather so far this year has been conducive to disease development.

The remaining leaves will develop black and yellow spots. Spraying with a fungicide at this point will not help, but give the affected tree extra care by providing supplemental water as needed and fertilizing in fall or next spring.

Consider replacing disease-prone trees with resistant varieties in the future.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.