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updated: 6/30/2013 12:06 PM

Grubs can cause brown patches

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By Tim Johnson
Chicago Botanic Garden

Grub problems vary from year to year and lawn to lawn. Grubs are the larvae of some kinds of beetles and feed on the roots of grass.

The adult beetles lay their eggs in early summer and are attracted to moisture. If the season is dry and yours is the only lawn on the block that is regularly watered, beetles will favor your lawn and you will have a greater chance of having grubs.

This year has been rainy, so grubs may or may not be a problem in your lawn. Deciding not to apply grub control will not necessarily result in a grub infestation. There is no need to control a small number of grubs, which the lawn can withstand.

If you do decide to treat for grubs, be sure to read the 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 from late June to mid-July.

Other products designed to quickly kill grubs may be applied later in season, if an infestation is severe enough to cause serious damage.

Often the first sign of the problem is when raccoons and skunks dig for grubs in the lawn. Typically, visible damage to the grass will occur when there are eight to 12 grubs per square foot. As hot and dry weather later in the summer increases the stress on the lawn, grass whose roots have been damaged by grubs will brown out quickly.

You can continue to install plants through the summer. Try to keep plants moist until you can plant them and water them right before planting. Plants that have been grown in containers can sometimes be difficult to remoisten if they are planted dry because they have a lighter growing medium that will generally dry more quickly than your garden soil.

New plants will need more frequent watering than established ones until their roots go out into the surrounding soil. Newly installed trees or shrubs that were balled and burlapped need the equivalent of 1 inch of rainfall a week.

The amount and frequency of watering will vary depending on the soil in your garden and weather conditions. Sandy, very well-drained soils will dry out more quickly than heavier clay loam soils. You will need to water more often if rain becomes scarce.

Prune out water sprouts (vigorous shoots on the inside of the tree and on the trunk) and suckers (vigorous shoots growing from the base of the plant) when you see them. Crabapples and hawthorns tend to send out lots of water sprouts and can benefit from this type of pruning.

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

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