The grubs of the Garden chafer are well controlled by the use
of the insect-parasitic nematode Heterorhabditis
bacteriophaga. Second and third instars are the most susceptable. Presently the
nematodes are mass-reared and in the market from 2000 onwards. At the end of July or the
beginning of August they can be applied with suitable spraying equipment or simply with a
watering-pot. The application rate is 500.000 per square meter.
Spraying equipment for distribution of nematodes is limited to certain conditions.
Nematodes are susceptable to dryness and direct sunlight (UV). Hence application should be
done at dusk or a cloudy sky. Insufficient soil moisture can seriously reduce nematode
efficacy so artificial rain is often needed. The long-lasting presence of the nematodes on
treated areas shows that nematodes have multiplied successfully in the grubs. Due to the
propagation and the winter-persistance, a perennial protection of turf against grubs is
expected. The field efficacy of nematodes against the Cock chafer and Summer chafer is
currently being investigated.
The succes of biological control with the parasitic nematode depends on the composition
of the grub species. Susceptable species are the Garden chafer and to a somewhat lesser
extend also the grubs of Hoplia philanthus, Serica
brunnea and Euchlora dubia. Before
applying nematods a specialist is needed for a proper identification of the grub. Aphodius
species are susceptable but do most of their damage in the cooler season. Nematodes prefer
soil temperatures above 15°C.
An effective way of control of Cock chafer has not yet been
found. It is generally advised to rain and roll the sward regularly. Biological control
with insect parasitic nematodes is still under research, however without results so far.
In Switzerland the a parasitic fungus (Beauveria bassiana) has been used giving
varying results. In Northern Italy trials have been made with nettings to prevent the
chafers perform the mating flight and foliage feeding. Application is limited to cash crop
like tree nurseries and orchards.
A few chemical compounds are known for their use against white grubs. By Dutch law no
chemical compound is allowed against white grubs. Generally the efficacy of chemicals
applied against white grubs in turf grasses is not very high. The use of chemical control
is dissuaded using biological control with the parasitic
wasp Tiphia femorata.
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