Larvae of June beetles, European chafers, and Japanese beetles are all known as white grubs.
- Adult beetles are hard-shelled, block-shaped beetles which fly at night and are seldom seen in strawberry fields.
- The larvae are found in the soil; they are C-shaped, with a tan or brown head capsule and six prominent spiny legs.
- Symptoms of white grub injury on strawberry plants include stunted growth and plant dieback.
Period of Activity
June beetle adults are active in late May and early June, European chafer adults are active in June and Japanese beetles adults are active in late July and August.
Eggs are laid in grassy places. The eggs hatch into larvae, or white grubs and feed on plant roots. European chafer and Japanese beetle larvae feed in late summer and again in the spring, until adults emerge. June beetle larvae remain in the soil for three seasons and feed on plant roots throughout each growing season.
First-year plantings are most susceptible to damage. Where plants show poor vigour or have wilted, collapsed and died, check the roots for damage and the soil around the plants for grubs.
ThresholdsNone established. In new strawberry plantings one grub can damage 3- 4 plants.
White grubs are the immature stage of scarab beetles, which include the June beetle, European chafer and Japanese beetle.
IdentificationThe larvae are found in the soil. They are C-shaped, with a tan or brown head capsule and six prominent spiny legs. They range in size from 2- 4 cm (1- 1 ½ in.) in length, depending on age and species. June beetle, European chafer and Japanese beetle larvae can be distinguished from each other by observing the pattern of stout spines (known as rasters) on the last segment of the abdomen. Adult beetles are hard-shelled, block-shaped beetles with long spiny legs.
|Distinguishing Scarab Beetles|
|Size||Colour||Period of Activity|
|June beetle||15- 50 mm (3/5- 2 in.)||Dark reddish brown||Late May and early June|
|European chafer||13 mm (1/2 in.)||Light brown||Mid June- mid July but variable|
|Japanese beetle||12 mm (1/2 in.)||Coppery metallic||Late July- early August|
Symptoms of white grub injury on strawberry plants include stunted growth and plant dieback. Roots can appear cut or sheared off a few centimetres (1 or 2 in.) below the crown. Injury usually occurs the year of planting. Affected plants suddenly wilt and die back. Plants are affected singly at first, then in groups in a row. In addition to root pruning caused by larvae, Japanese beetle adults may feed on strawberry foliage, causing a lacy shredded effect.
Damage is most common in lighter soil types when strawberries are grown after pasture, sod, or occasionally after a grain crop.
Often Confused With
Root weevil larvae (Both feed on plant roots as larvae. White grub larvae have prominent legs and claws and are found in new plantings after sod or other grassy or weedy crops. Root weevil larvae are legless, generally smaller than white grubs, and more likely found in older plantings.)
Verticillium wilt and black root rot (Both diseases attack the root system and cause similar symptoms above ground.)
Adults are active in late spring or summer. European chafer and June beetle adults fly at night and are attracted to lights. Adults hide in the soil during the day and fly to trees to feed at night. They are seldom seen in strawberry fields. Japanese beetles fly on warm summer days and sometimes feed on strawberry foliage.
The adult beetles usually lay their eggs at the beginning of summer in soil, sod or other grassy places. It takes 2- 3 weeks for the eggs to hatch. The larvae feed on the roots of strawberry plants throughout the summer. Come colder temperatures, they bury themselves deep in the soil and overwinter. In spring, they migrate to the root zone to feed. By this time they are larger and therefore cause more damage than the previous year. European chafer and Japanese beetle larvae stop feeding, pupate and emerge from the soil in late spring. June beetle larvae continue to feed for 2 full years. They overwinter a 2nd year, feed briefly, pupate and emerge as adults the following spring (late May- June).
Period of Activity
June beetles are active in late May and early June. European chafer adults are active in June and Japanese beetle adults are active in late July and August. European chafer larvae and Japanese beetle larvae feed in late summer and again in the spring, until adults emerge. June beetle larvae remain in the soil for three seasons and feed on plant roots throughout each growing season.
Where plants show poor vigour or have wilted, collapsed and died, check the for damage and soil around the plants for grubs. First-year plantings are most susceptible to damage.
Use a hand lens to identify which kind of white grub is present. Knowing if the problem is caused by European chafer or by June beetle larvae will assist the grower with management decisions.
None established. In new strawberry plantings one grub can damage 3- 4 plants.
- Do not establish new plantings for two years after sod or pasture crops.
- If white grubs are noticed when a new field is prepared for planting, delay planting. Work the field for a few more weeks to encourage birds and other predators to feed on the grubs.
- Keep grassy weeds under control to make the habitat less favourable for white grubs.
- There are no insecticides registered for white grub control on strawberries.
- Grass parking lots can serve as a large reservoir for the build-up of grubs. Treat these grass areas like turf or lawns but do not treat inside the planting.