Spring infections often lead to summer, fall leaf damage

Hawthorns with a more severe case of cedar apple rust may have leaves that turn bright yellow and drop prematurely. There will be small yellow spots that appear on foliage after infection in spring. This disease requires eastern red cedar (Juniperus virginiana) as an alternate host, so avoid planting this plant if you have hawthorns in your garden. Like the crabapples, spraying now will not help your trees, as controls need to be applied in spring to prevent these diseases.

• Some crabapples are very susceptible to apple scab and those not treated in spring may have lost many of their leaves. Their remaining leaves can be affected with black and yellow spots. Spraying at this point will not help combat this disease but you can give the trees extra care by supplemental watering as needed for the remainder of this year and fertilizing in fall or next spring.

Remove all infected leaves and do not add them to your compost pile. Also, consider replacing disease-prone trees with a cultivar that is resistant.

• Holes in the lawn dug by raccoons and skunks may indicate the presence of grubs, which feed on grass roots. Check for areas of the lawn that are browning or where the grass lifts like a piece of sod. If there are more than 12 grubs per square foot and you are seeing extensive damage, then you may consider using a product designed for quick kill of the grubs. Be sure to read the bag carefully to ensure you are buying the right chemical for grub control at this time of year. It is important to follow the instructions for application.

• Continue to monitor plants you have installed over the last couple of years and provide supplemental water as dry conditions continue. Check the soil if you are unsure of the need for additional water. Keep in mind that a light rainstorm may not be enough to adequately water plants that are still establishing in your garden.

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