Species

White grubs (Phyllophaga spp. and Polyphylla spp.) belong to the order Coloeptera and the family Scarabaeidae. Adults are known as "June beetles."

Host/Site

Found in soils of potatoes, corn and fruits, and soils of ornamentals such as rose, ash, elm, poplar, walnut, oak and locust. Grubs are also very common turfgrass pests.

Identification

Appearance Only the larvae are known as "white grubs." They are "C-shaped," 25-50 mm in length and, as their name implies, white in color with a brown head. Larvae have three prominent pairs of legs. Adults are typical of scarab beetles, 25-30 mm long and are dull or metallic brown in color.

White grubs (June bug larvae) Photo Courtesy of Steven Katovich, USDA Forest Service

Adult June Beetle Photo Courtesy of Steven Katovich, USDA Forest Service

Indicators
Larvae feed on roots, while adults feed on foliage. A lawn infestation often resembles drought damage causing grass to thin, yellow, and die. Eventually brown patches of dead grass will occur and grow in size as the infestation grows. Gras will also pull up easily due to the root damage inflicted by the grubs. Injury inflicted by larvae can severely injure or kill plants.

Life Cycle

Eggs are laid by females in groups of 35-60 in the soil in June and July and hatch in 3-4 weeks. After hatching, larvae feed on vegetable matter in the soil until winter approaches. Larvae then dig deep into the soil and lay dormant until spring, when they emerge and feed on roots and tubers. This second year of larvae development is when the most damage occurs. The larvae overwinter again and will pupate in later summer of the third year. Pupae are found one to two inches in the ground and are cream colored, but darken before emerging as adults.

Natural Enemies

Predaceous Ground Beetles and [toxipedia:ants] are effective predators. Certain species of Parasitic Wasps and nematodes prey on white grubs.

Monitoring

If there is a suspected turfgrass infestation cut away a 1 sq. foot section of soil to assess grub populations. With a spade cut three sides of a square one foot deep. Peel this piece back and look for larvae, pupae, and adults. This should be done in August when grubs are large enough to be seen easily. When finished place the grass back in it place and water.

Action Threshold

Fewer than 5 grubs per square foot is a low population density and requires no action. Typically 8-10 grubs per square foot is the threshold at which control action should be taken, but this may be significantly lower if vertebrates such as raccoons, skunks, birds or moles are digging up soils to access grubs.

Physical/Mechanical Controls

Young larvae are extremely susceptible to drying out (desiccation) in July and early August. If your crop or turfgrass can withstand water stress, think about watering less. Lawns are hardy and will come back from drying out. In the Pacific Northwest, letting your grass slow down and dry in the summer and then come back naturally during the wet fall and winter is a common method to avoid dealing with these infestations.

Biological Controls

Parasitic Wasps such as Tiphia spp. control white grubs, although they may take two to three years to build up to populations.

Parasitic Nematodes of the genera Steinernema (also known as Neoaplectana) and Heterorhabtitis can be effective, although they may have to be applied annually.

Encourage populations of [toxipedia:ants] and Predaceous Ground Beetles, as both are predators of white grubs.

Chemical Controls

Since white grub infestations are generally sporadic and can occur unexpectedly spraying pesticides in anticipation of an outbreak is not recommended. Spraying during an infestation can kill both white grubs as well as other beneficial insects and is also not recommended.

References

Buss, Eileen. "White Grub Biology and Management." 2008. University of Florida IFAS Extnesion. 30 Oct 2008. < http://edis.ifas.ufl.edu/LH037>.

Berry, Ralph. "White Grubs." 1998. Insects and Mites of Economic Importance in the Northwest. 23 June 2008. <http://pnwpest.org/potato/whitegrubs.pdf>.

Shetlar, David. "White Grubs in Turfgrass." Ohio State University Extension.
23 June 2008. <http://ohioline.osu.edu/hyg-fact/2000/2500.html>.