Older varieties of crabapple trees are susceptible to disease

As leaves emerge, it is time to begin spraying crabapples that are susceptible to apple scab.

Typically, this disease affects older varieties of crabapples. If your tree's leaves were covered with black spots and fell off in late summer, the tree needs a protective spray program or should be replaced with a new, disease-resistant cultivar.

Begin spraying after the buds open and treat once every seven to ten days until the leaves are fully open. Generally, three treatments suffice.

Email plantinfo@chicagobotanic.org for recommended fungicides and timing for applications.

• Use an electric hand grinder to sharpen your spades. Wear ear and eye protection while doing this work. Keeping the spades sharp will make gardening much easier. Note that new spades do not come with a sharp edge.

• Apply pre-emergent crabgrass control only if you had issues with crabgrass in your lawn last year. A pre-emergent herbicide works by preventing weed seeds from germinating, so it needs to be applied before germination occurs.

The cool weather has been slowing things down some this year, so there still should be time to apply. Early to mid-April is the typical application window, but you can also plan to apply the chemical before you see lilacs begin to flower.

Pre-emergent herbicides also prevent grass seed from germinating. Once applied, avoid disturbing the lawn surface, as the product forms a barrier at the soil surface to prevent seeds from germinating.

• When turning on your irrigation system for the first time this year, monitor each zone to ensure uniform coverage. Sprinkler heads can become plugged or not rotate properly, leaving dry areas.

Soft, excessively wet spots in the lawn can indicate a leak in the system. Adjust your system to the generally cooler and wetter spring growing conditions to water less to avoid overwatering your garden and wasting water.

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