Late-summer humidity can cause a problem for some plants

Powdery mildew - a disease that causes a grayish, powdery film on leaves - is present now. Common plants that can get powdery mildew are lilacs, phlox, bee balm, zinnias and nannyberry viburnum.

This disease typically occurs in the late summer when the weather is warm and humid. Fungicides can help control powdery mildew if applied before the infection becomes severe. In most cases, there is no need to apply any controls for powdery mildew at this time of year.

Other options include selecting more mildew-resistant varieties or moving the infected plants to an area of the garden that has better air circulation.

• Crabgrass may be evident in your lawn now, especially if it has been neglected. This annual weedy grass seeds readily in the fall.

Keep your lawn closely cut to prevent seed formation or pull crabgrass out by hand. There are herbicides that control crabgrass, but they are not as effective after the crabgrass has set seed.

Make note of bad areas in your lawn and apply a pre-emergent herbicide (one that prevents weed seeds from germinating) in early spring before lilacs flower.

• It is time to order spring-flowering bulbs early to ensure the varieties you want are available. Choose a site with well-drained soil. Any area in the garden that remains wet for long periods - or has standing water for any length of time - is unsuitable for bulbs.

Bulbs prefer moisture in spring and fall and dry conditions in the summer. Most prefer full sun. When planted beneath a high branching tree, early spring bulbs will flower before the tree leafs out and will mature before the shade gets too deep.

Summer snowflake (Leucojum aestivum) does have some tolerance to moist conditions.

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