If you want to panic the homeowner of a well-manicured lawn, just yell, “Grubs!” White grubs are the most destructive turf insect pest in Illinois. However, not all turf areas will get grubs, and the extent of grub damage varies from year to year.
White grubs, which represent the larval stage of beetles, are creamy-white in color, with a C-shaped body, brown head, and short legs. The most common grub species are the annual white grubs that become adult Southern and Northern masked chafer beetles and Japanese beetles.
Grubs feed on turfgrass roots and other organic matter in the soil. The damage initially appears as brown areas of the lawn, similar to the look of drought stress. Continued feeding will cause the turf to die in irregular patches. This turf can often be rolled back like a loose carpet.
So do you need to treat your lawn for grubs? Egg-laying beetles are attracted to well-watered or moist areas of turfgrass that get full sun. Those of us who didn’t water our lawns are less likely to have a grub problem.
If you have an irrigated lawn, where you know you should have a grub problem, July is generally the time to apply an insecticide. Application of imidacloprid (one brand name is Merit) or halofenozide (GrubEx) in July to irrigated turf should provide control. These two insecticides may take as long as three weeks to kill grubs but last for months in the soil. They are most effective on small, newly hatched grubs.
If you have not watered your lawn this year, wait to apply an insecticide until after grubs emerge. In early August, scout for grubs by sampling square-foot areas around your lawn. Cut through the turf with a heavy knife on three sides of a square, then peel back the turf. Grubs will show up in or just below the turf’s root zone. If the soil is dry, the grubs may be 2 to 4 inches deeper. Check for these deeper grubs by tilling up the soil with a knife.
A well-managed lawn can withstand a number of feeding grubs without suffering great damage. Typically a population of 10 to 12 grubs per square foot causes obvious turf damage. Eight to 10 grubs per square foot may cause injury in heavily used turf. If control is warranted, apply trichlorfon (Dylox). Grubs must be present when Dylox is applied to be affected by it. Only treat in and around affected areas.
Once you’ve applied a granular insecticide, you should apply at least a half-inch of water to move the insecticide into the root zone, where the grubs will come into contact with it. Before applying any chemical, read and follow all label directions.
For more information and to view a photo of an annual white grub, visit the grub page on the University of Illinois Extension Web site, www.urbanext.uiuc.edu/turf/whitegrub.html.
U of I Extension entomology specialist Phil Nixon provided information for this article.
Flowers at the fair
Next week, as you make your way through the maze of tents, livestock buildings, and food stands at the fairgrounds, take note of the beautiful flowers.
Bright red and orange cannas, yellow marigolds, blue salvia, and white petunias are just a few of the 150 different kinds of flowers on display. Flowerbeds — 226 in all — are tucked in every corner. This year, the flower displays feature for the first time artfully displayed antique farm equipment.
Look up and see one of the 175 hanging baskets, some of which contain trailing pink and purple petunias. Along the avenues are 65 concrete planters, some bursting with tall orange cannas and cascading black sweet-potato vines.
Inmates at the Lincoln Correctional Center started the 150,000 flowers from seed in March. Each day during the fair, a dozen Logan Correctional Center inmates care for the flowers under the watchful eyes of corrections officers.
If you need help identifying flowers or have any gardening questions, see a master gardener at the University of Illinois Sangamon-Menard Unit, in Building No. 30, along Eighth Street. They’ll be there each day, 8:30 a.m.-4:30 p.m