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Lawn & Turf Tips:  White Grubs

White Grubs

Grubs are white to cream-colored C-shaped pests (1/4 inch to 1 1/4 inches long) that feed on the fibrous roots of grass and sometimes other plants. Their bodies are white with six legs and a dark head and usually lie in a curled or C-shaped position. They are immature (larval) stages of May/June or Japanese beetles from the scarab family. Turf grass damaged by white grubs has a reduced root system and is easily pulled away from the soil.

Symptoms and Damage

It is normal to find a few white grubs per square foot in lawns. The mere presence of grubs is not necessarily a cause for concern, because healthy turf can easily outgrow the root loss caused by a small number of white grubs. They are one of the most destructive insect pests of turf because feed on grass roots causing severe wilting and eventually death of affected lawns.
The damage appears first as drought stressed.

  • When the turf is heavily infested, it may first appear off color then wilts quickly but with continued feeding, the turf dies off in large irregular patches.
  • With the tunneling and burrowing of the grub, the turf tends to feel spnge and rolls back like a carpet.
  • Another indication that white grubs may be present is moles, skunks, raccoons, or flocks of blackbirds finding the turf attractive.

Life Cycle Stages

The scarab family has a complete lifecycle starting with eggs, larvae, pupae and adults. The May/June beetles have a 3 year life cycle. Japanese Beetles have a 1 year life cycle. Most scarab beetles winter over in the soil; however, the May/June beetles winter over as adults.

  • Eggs: The eggs are a creamy-white and about 1/16-inch long. They are slightly oval when they are first laid in the soil. Once laid, they absorb water from the soil and become slightly swollen and rounded.
  • Larvae: The larvae is c-shaped and referred to as grubs. They are thick with creamy-white bodies. They have a brown head capsule and short legs. The larvae have 3 instars meaning they molt 3 times.
  • Pupae: These tend to be slightly longer than the adults. Their bodies are formed in chambers approximately 1- 2 inches below the soil surface. They start out cream colored and then darken before they emerge as adults.
  • Adult: The adults are oval shaped with the atennae ending in a large club of flattened plates. The May/June and Japanese beetles are the most common types of scarab in our area.

Identification

The best way to identify if you have grubs is to cut three sides of a 12 by 12 inch square (30 x 30 cm) and 4 inches (10 cm) deep piece of sod. You may notice that the sod just rolls up like carpeting. Once you have lifted the sod piece. Check through the top 4 inches of the turf you pulled up. If you have 3 or more grubs in a 12x12 inch area, you should consider treatment. Do this same process in several spots throughout your lawn.

 

Types of Control

A wide array of variables can influence the severity of damage from white grubs. When they are abundant, applying a soil insecticide may be the only way to avoid serious damage to the turf. If you do have them, you can protect your lawn by promptly treating the problem. Most lawn grasses are subject to attack by grubs. When their populations are low, treatment is not usually needed. Just overseeding these damaged areas without removing the grubs will not be successful as the white grubs will soon eat the new grass seedlings roots. Once the white grubs have been treated or removed you can then proceed with making repairs. There are several strategies that can be used to control grubs.

  1. Chemical Control #1: If three-year white grubs are found in densities exceeding three per square foot, an insecticide should be considered (liquid, granular or seed treatment insecticide). This application of insecticide is done when the grubs are present near the soil surface and actively feeding. If the infestation is severe, you may need to do a second application either later in the year or the following year to kill the grubs that were not at the soil surface during the first application. Proper timing and chemical application are critical to suppressing them.
  2. Chemical Control #2: If you have had a problem with grubs in the past few years, you may want to put down a preventative grub control on your lawn. This is typically applied in early June.
  3. Cultural controls: Although all turf can be a victim of grubs, you can discourage them from calling your lawn home by having a well-fertilized and aerated lawn with deep root growth. The eggs require soil moisture in order to hatch. If your lawn healthy and can withstand going with out watering, it is recommended that you not water your lawn during July and early August when the beetles are laying their eggs. It takes about 2 weeks for the eggs to hatch.

In contrast, when the grubs are feeding in mid-August and September, maintaining good watering habits and adequate fertilizing applications will help the turf recover quicker and minimize the damage.

As always, early detection of grubs will help minimize the damage that can occur from an infestation. If you suspect that you have a grub problem, please call us so we can come out to identify them and share with you your best options.