Beginner

Scientific Name
Phyllophaga spp

Identification
Life stages: eggs, larvae, pupae, adults.

Eggs are pearly white, about 2.5 mm in length and 2.0 mm in width.

Larvae or grubs have C-shaped white bodies with reddish brown heads and brown legs. The end of the abdomen is dark brown. When mature, grubs are about 3 cm in length.

Adults: The adult stage of white grubs is the June beetle. Beetles are light to dark brown and measure about 2 cm in length and 1cm in width.

Often Confused With
White grubs of other species

Period of Activity
June beetle larvae are present in the soil for 3 years.

Feeding is most noticeable in late spring. However, feeding damage may occur throughout the growing season.

Scouting Notes
Correct identification of white grub species is important in determining management strategies.

To identify the species of white grub, examine the hairs and sutures on the last abdominal segment on the grub’s body. The raster pattern is the arrangement of bristles and hairs on the underside of the tip of the abdomen.

A 10x hand lens is needed to see this pattern on most mature white grubs. A microscope may be necessary to view smaller grubs.

Estimates of white grub infestation in soil are done by taking soil samples to a depth of 30 cm. The soil samples are examined and larvae counted.

Thresholds
Economic damage may be severe when there are more than 4 white grubs/ft2.

Advanced

Scientific Name
Phyllophaga spp

Identification
Life stages: eggs, larvae, pupae, adults.

Eggs are pearly white, about 2.5 mm in length and 2.0 mm in width.

Larvae or grubs have C-shaped white bodies with reddish brown heads and brown legs. The end of the abdomen is dark brown. When mature, grubs are about 3 cm in length.

Adults: The adult stage of white grubs is the June beetle. Beetles are light to dark brown and measure about 2 cm in length and 1cm in width.

Often Confused With
White grubs of other species

Biology
The larvae of June beetles are the most important white grubs attacking potatoes. White grubs prefer sandy soils and are rarely pests in heavy, poorly drained soils. They are most likely to damage potatoes growing in land previously in sod. The common June beetle occurs throughout Canada and almost everywhere in the United States.

The grubs chew deep cavities in the tubers, making them totally unmarketable.

The life cycle of this insect lasts 3 years.

• First year: In the spring, the female beetles lay eggs in grassland or in patches of grassy weeds in cultivated fields. Small, white grubs hatch in 2–3 weeks and feed mainly on fine roots. The larvae then move down into the subsoil for the winter.
• Second year: As the soil warms the following spring, the small grubs move upward to feed on roots and tubers, causing severe damage. The grubs, nearly full grown, remain in the soil for the second winter.
• Third year: Early in the summer of the third year, the grubs pupate. Later in the season, the adults emerge, but remain inactive buried in the soil. The adult beetles overwinter in the ground, emerging the following May and June.

Period of Activity
June beetle larvae are present in the soil for 3 years.

Feeding is most noticeable in late spring. However, feeding damage may occur throughout the growing season.

Scouting Notes
Correct identification of white grub species is important in determining management strategies.

To identify the species of white grub, examine the hairs and sutures on the last abdominal segment on the grub’s body. The raster pattern is the arrangement of bristles and hairs on the underside of the tip of the abdomen.

A 10x hand lens is needed to see this pattern on most mature white grubs. A microscope may be necessary to view smaller grubs.

Estimates of white grub infestation in soil are done by taking soil samples to a depth of 30 cm. The soil samples are examined and larvae counted.

Thresholds
Economic damage may be severe when there are more than 4 white grubs/ft2.

Management Notes
Planting potatoes in recently ploughed grass sod should be avoided. Infested fields should be harrowed, which kills the grubs by physical injury or exposes them to natural enemies and the elements. Tillage should be timed between early May and late June to kill the second year grubs and from late July to early September for first year grubs.