The European Chafer, Rhizotrogus majalis, is a serious pest of turf, horticulture, and field crops 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 present throughout Vancouver, Burnaby, and Coquitlam. It has been confirmed in east Richmond (2010) and North Delta (2007).
The adult beetle (Figure 1) is tan coloured and resembles a small June beetle (12 mm long). The larvae, or grubs (Figures 2, 3), have a C -shaped body and brown head. Mature chafer grubs are up to 25 mm long, significantly smaller than mature June beetle grubs. A microscope is required to confidently identify the grubs.
||Figure 1: Adult European Chafer.
||Figure 2: Mature European Chafer grubs
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.
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, blueberries, strawberries, conifers, 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 in turf or other crops. Considerable damage to turf can occur in the fall and winter from animals, including skunks and birds digging up the grass to feed on the larger grubs (Figure 4). The adult beetles are active at dusk and can be seen in groups in deciduous trees, but they do not cause damage.
||Figure 3: European Chafer grubs in turf
||Figure 4: Boulevard damage caused by skunks digging out grubs.
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.
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 and grubs have pupated.
There are some naturally occurring soil organisms that infect European chafer larvae and make them sick, reducing their impact. However, these cannot be relied on to completely manage a chafer infestation.
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. Do not remove soil from infested areas, as chafer can be spread to new areas by movement of infested soil. Do not import plants from infested areas. Composting will not kill larvae.
Updated April, 2010