The European Chafer, Rhizotrogus majalis, is a serious pest of turf in
Eastern North America. In 2001 it was found in New Westminster, British
Columbia, in lawns and boulevards. It is slowly spreading and is now throughout
Vancouver, Burnaby, and part of Port Coquitlam. In 2007, it was detected at one
site in Delta.
Description
The adult beetle (Figure 1) is tan coloured and resembles a smallish June beetle. The larvae, or grubs (Figures 2,3), have a C -shaped body and brown head. Mature chafer grubs are smaller than mature June beetle grubs. A microscope is required to confidently identify the grubs.
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Figure 1: Adult European Chafer. |
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Figure 2: Mature European Chafer grubs |
Biology
The European Chafer completes a life cycle in one year. Eggs hatch around mid-July, and the grubs moult twice over 8 weeks. The mature grubs are well adapted to cool moist conditions and feed all fall. During the winter they dig down during periods of freezing conditions, but otherwise remain within 5 cm of the surface. They feed in the spring until April when they become pupae. Adults emerge in late May, fly to nearby deciduous trees to mate and feed, and subsequently females deposit up to 50 eggs each.
Damage
The grubs are the damaging stage. They feed on all types of grass and, if
numerous and food is scarce, may move into vegetable plantings to feed on corn,
potatoes and other crops. European chafer grubs prefer to feed on fibrous roots,
and can damage ornamental and nursery plants by reducing their fibrous root
system. Most of the damage is done by the third (final) instar grubs in the fall and early spring, but damage can be masked by the abundant moisture at these times. Drier weather can quickly result in the
appearance of brown, dying patches. Considerable damage to turf can occur in the fall and winter from animals, especially skunks, and birds digging up the grass to feed on the larger grubs (Figure 4).
The adult beetles feed at dusk on the leaves of deciduous trees but, even when numerous, seldom cause significant damage.
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Figure 3: European Chafer grubs in turf |
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Figure 4: Boulevard damage caused by skunks digging out grubs. |
Monitoring
To check for grubs, cut 3 sides of a 30 by 30 cm piece of sod to a depth of 5 cm, and fold it back to count the grubs. Generally if more than 20 grubs are found, control is warranted.
Management
Healthy, vigorous, well-irrigated turf can withstand low levels of grub
feeding. Mow at 6-9 cm height, as taller turf is less preferred by
egg-laying female beetles, and is more drought tolerant. Although birds
and mammals feeding on larvae damages turf, it also helps decrease the
pest population. Do not reseed until feeding is completed.
Conventional insecticides and predatory nematodes are available for grub
control. Both types of products work best if applied when grubs are small; from
late July until September. Local studies show that Heterorhabditis
bacteriophora is the best nematode choice (one trade name is Nemasys G).
This nematode is a "cruiser" species that actively seeks out white grubs such as
the European Chafer, and quickly destroys them from the inside-out. Carbaryl is
available in domestic formulations, which homeowners can purchase and apply.
Imidacloprid and chlorantraniliprole, in addition to carbaryl, are available in
commercial formulations, which can only be applied by commercial applicators.
Insecticides can also be applied successfully to non-frozen turf in the fall
and early spring. Before applying treatments, remove excessive thatch and
irrigate if the soil is dry to bring the grubs to the surface. After applying
either a conventional insecticide or nematodes, water the treated area to move
the product into the root zone. See labels for more details.
If you have an ongoing problem with European chafer, consider employing a
commercial lawn care company to help manage the problem year round.
Alternatively, remove turf from chafer-prone areas and replace with an
alternative landscape feature.
Updated August 26, 2008
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