Check magnolias for insects
This is the time of year to check closely 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 presence of this black mold on other types of trees can also indicate problems with other insects.
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.
• If your garden was flooded, then give your plants some time to recover and remove any excess debris out of the beds. The longer the plants were inundated with water, the more likely they will be damaged. Different types of plants will vary widely in their ability to withstand being flooded. Hostas and day lilies that were flooded at the Chicago Botanic Garden are currently looking OK while plantings of dahlias and salvia were quickly killed. Some shade trees are showing early fall color as a stress response to being flooded.
If you are unsure whether a perennial has died because of flooding, cut back the dead foliage and observe the plant over the next few weeks to see if it pushes new growth. Any flooding damage to trees and shrubs will show up over the coming weeks. Any decisions to remove plants will depend upon the extent of the damage, which is difficult to predict at this time. In most situations, it is not worth trying to wash dried silt off the foliage of plants.
• Continue to groom your perennials and annuals by removing yellowing foliage and spent flowers. Make note of perennials that have flopped and need staking so a support system can be installed next spring before the plants actually need it. Gentle pruning back of more vigorous perennials can help keep your border from looking overgrown. Cutting leaves off at the base can reduce the size of the plants without having them look pruned. You may want to let certain dried flowers on plants such as astilbe and coneflower remain standing for fall and winter interest. Goldfinches visit my coneflowers in fall and eat the seeds.
• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.