Grubs can become a lawn pest

Grubs can be a problem in lawns some years. The adult beetles are attracted to irrigated lawns that are surrounded by dry lawns for their egg laying in early summer. If the season is dry and you are the only one on the block watering your lawn, the chance of having grubs increases.

The rainy spring this year reduced the chances of a concentrated outbreak of grubs. Deciding not to apply grub control will not necessarily result in a grub infestation. Typically, when there are eight to 12 grubs per square foot, visible damage occurs as they feed on the roots of the grass. The lawn will brown out later in the season when hot and dry weather increases stress on the lawn.

Raccoons and skunks dig in lawns to eat the grubs; this is often the first sign of the pest. Be sure to read the insecticide label carefully to make sure you are using the right product at the right time of year. Products designed to prevent grubs are generally applied between late June and mid-July.

There are products designed for quick kill of grubs that are applied later in the season when grubs reach a threshold in the lawn that is causing damage. There is no need to control a small number of grubs that the lawn can withstand.

In any case, use an insecticide labeled for grubs at the proper time of year. I do not irrigate my lawn at home and have never treated for grubs and have only had a minor problem once.

• Some varieties of crabapple are very susceptible to a fungal disease called apple scab, and those not treated in spring may lose their leaves at this time. The remaining leaves develop black and yellow spots. Spraying with a fungicide at this point will not help.

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.

• Watch for spider mite damage on your plants. The small spider mites can be detected by taking a piece of white paper and striking some plant foliage on it. The mites can be seen moving slowly on the paper.

Populations can build quickly, especially during hot, dry spells of weather. Mites feed on leaves, causing fine spotting on the foliage. Where large populations attack, injured and chlorotic areas can join, causing large portions of the leaf or the entire leaf to turn yellow or bronze.

It is not uncommon to find hundreds of mites and eggs on a single leaf. Webbing may be visible, but the silk-producing habits of spider mites vary.

Use a jet of water to knock the spider mites off the plant instead of chemical controls to preserve natural predators. Insecticidal soap, summer weight horticultural oil, or a miticide spray may be needed if populations are large. Be sure to read and follow label instructions to maximize effectiveness and to avoid damaging the plant.

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