Field Guide     Pest Management     White Grubs

White Grubs

CROPS IMPACTED: Turf grass

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Family: Phyllophaga

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About White Grubs

Reproduction and Life Cycle

The white grub has been associated with different beetle types; however, its true adult form is the May (or June) beetle. It takes this beetle 3 years to fully develop. They mate during the evening hours; the females will lay their eggs by dawn. Eggs are laid in the soil 1 to 8 inches below the surface, in clusters of between 15 and 20. If eggs are laid in a wooded area, they will be closer to the surface. In 3 weeks the eggs will hatch. The new larvae immediately begin to feed on plant debris and roots that are available to them. In the fall, larvae will burrow into the soil up to 1.5 meters deep, and will overwinter there until spring. They will then tunnel back up to the surface and continue to feed on plant roots; this is often when the grubs cause the most damage. They will remain larvae for that entire growing season. In the fall, they once again burrow into the ground to overwinter. When they surface the following spring, they continue to feed on roots until early summer, which is when they reach full development as larvae. They then pupate in the soil. This stage takes several weeks to complete. When the adults emerge, they remain in the ground so that they can use it as an overwintering site. When the following spring comes around, they begin to feed and then mate, continuing the cycle.

White Grubs Identification and Habitat

Identification

The adult May beetle can vary between 12 and 25mm in length. They are commonly dark brown to yellow in color, with a tough, shiny outer shell and are rectangular in shape. The larvae are also quite long, usually between 20 and 45mm. As the name states, this grub is white in color and is curved in a C shape. Their heads are brown and have 6 legs near the head. The rear segment of the body appears slightly larger, and is darker because of the transparent wall, showing you the soil inside that the larvae consumed. To help distinguish this larva from other types similar in appearance, look on the underside of the last segment of the abdomen; white grubs will have 2 strips of spines parallel to each other. The pupae are around 22mm long. They are usually either pale yellow or brown. White grub eggs can have a diameter of up to 3mm in length. They resemble the shape of a small sphere and start off white but will continue to grow darker as they mature.

Habitat

This pest can be found throughout North America. It will feed on the roots of turf grass, creating spongy sod when infestations are bad. To know whether or not you have an infestation, look if your lawn has dying patches of turf. Damage is witnessed most in the early spring and fall. Another indication of an infestation is a strong presence of moles, crows, or skunks near your turf. While white grubs prefer grass, they have also been known to feed on other plant roots such as weeds, and different types of vegetable plants.

White Grubs Management and Control Methods

Cultural Control

To control white grubs in your fields, you can plow in early fall or late spring as this kills numerous pupae, grubs and adults in the soil. This also helps to expose this pest to natural predators. If you use reduced or no-tillage practices for your crops, this will increase white grub populations. Parasitic wasps such as Pelecinus polyturator Drury, and Tiphiaand Myzinum help control this pest. Also, the fungus Cordyceps, and the bacteria Bacillus popilliae Dutky can kill off larvae, which can be purchased commercially. You can also purchase nematodes, specifically Steinernema carpocapsae. Make sure to handle the nematodes with care as they are a living organism and can be killed if handled roughly, making this control method ineffective. If using nematodes, ensure to keep the treated soil moist to contribute to healthy nematode growth. Note that having satisfactory control of this pest is often dependent on using an integrated management system that includes the use of both cultural and chemical methods.

Chemical Control

To control the white grub chemically, products such as triclorfon (Dylox) the organophosphate or carbaryl (sevin) have shown to be effective against this pest. However, note that carbaryl can be damaging to earthworms and does not have as high of a success rate as triclorfon. Make sure to water the treated soil before and after application, as this will improve its effectiveness. There are also different chemicals you can use as preventative measures against this pest. Chloranthaniliprole (Acelepryn), clothianidin (Arena), imidacloprid (Merit), thiamethoxam (Meridian), or a combination of clothianidin and bifenthrin (Aloft), or imidacloprid and bifenthrin (Allectus) are some good examples. These preventative insecticides should be applied before white grubs hatch from their eggs. The benefit of using preventative measures instead of curative is that for prevention, typically less of the chemical needs to be applied and thus, is more environmentally friendly. Preventative measures should be taken in areas that have been known to have damaging levels of white grubs, or where infestation is likely to occur. For any pesticide you use, always be sure to carefully read all labels for cautions and proper application.

Latin / Alternative White Grubs Names

  • - Scarabaeidae

Sources

http://entnemdept.ufl.edu/creatures/field/white_grub.htm

http://www.ladybug.uconn.edu/WhiteGrubs.htm

http://www2.ca.uky.edu/entomology/entfacts/ef441.asp