Understanding the Dangers of Pesky Grubs

BY RON FISTER

Plots of green turf, small or large, can be useful assets in our landscapes. They serve to blend beautiful shades of green against other colors of nature and gardens, providing a pleasant visual effect.

However, subsurface pests — many species of beetles, mainly belonging to one family — enjoy turf even more than we do, because turf roots serve as their food source, as well as a nice place to rear their offspring. Soil insects live in a rich environment of carbon, microbes, water and nutrients. Their grubs damage turf below the ground, and the adult beetles emerge in early- to mid-summer to cause additional damage to plants above the ground. This often is when we take most notice of them — when we see them feeding on roses, blackberries, grapes and crape myrtles, to name a few.

During that time, beetles begin to live out their life cycle by mating and laying eggs for the next season’s offspring. Turf is an ideal home for their reproductive cycle, as rainfall, hot weather and dry conditions do not slow the process.

From late May through June, the soil-inhabiting insects begin their metamorphosis from grub (larvae, third instar) to adult beetles as they emerge from the thatch layer of turf.

Regardless of the specific beetle, the grub larvae stages are similar in appearance, ranging from ½-inch to ¾-inch long. They are white to grayish in color, with brown heads and six distinct legs. And they are characterized by the C-shape position in which they feed on turf roots.

You might see them in landscape environments as you begin to get active gardening in the spring. Severe infestation of grubs feeding on turf roots can produce stressed turf, which causes sod to turn brown and die. However, don’t confuse dying turf from grub damage with winter diseases in the turf.

Generally, grub damage is not noticed until the late winter and early spring as we walk across our lawn and notice spongy surfaces caused by moles tunneling through the lawn searching for grubs.

Controlling these subsurface insects in the spring can be costly and have negative effects on the environment. The ideal time to treat the beetles (grubs) that harm turf is August and September, after egg laying or the first instar (the developmental stage after hatching) of the insect.

There are various granular insecticides to use for control of white grubs, Japanese beetle larva, European chafer, Southern chafer and billbugs. The University of Georgia’s recommendation is to look for the following active ingredients and brands when choosing an insecticide:

• Carbaryl — Sevin and other brands.

• Dinotefuran — Safari 20SC by Green Light.

• Trichlorfon — Dylox and other brands.

• Imidacloprid — Merit and other brands.

• Halofenozide — Mach II, Grub B-Gon and other brands. Read the label for application instructions. Water the lawn before application of any controlled material, and water thoroughly following insecticide application.

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