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Fly Management Techniques

11 June 2013

Measures for fly prevention on farms and control measures are outlined in 'Fly management: How to comply with your environmental permit' from the UK's Environment Agency.

In practice, successful fly management is likely to involve the co-ordinated use of a range of both non-chemical and chemical fly control techniques.

The COSHH Regulations 2002 impose a requirement to consider using non-hazardous pest control techniques in preference to potentially harmful pesticides. Where suitable techniques exist, pro-actively preventing fly problems is a more effective and sustainable approach than trying to deal reactively with an established infestation of flies. Typical permit conditions require prevention of nuisance, where possible.

Fly Prevention and Appropriate Measures for Poultry Facilities

The key to avoiding fly infestations is managing water and moisture in the manure. Premises which keep manure dry or regularly remove it rarely experience serious infestations, and almost never need to use insecticides. All installations should aim to achieve this situation.

High risk periods for fly infestation in poultry laying units are the first few months after a new flock has been introduced, where that period coincides with warm weather. For example, introducing a new flock into a house in April poses a risk of fly problems within a few weeks that may then persist for most of the summer. This is a result of the combination of rising temperatures, low initial predator numbers, and manure that tends to be wet in the initial period whilst the flock settles.

Operators should ensure they have a sufficient stock of insecticide products, and the resources to use them if required, over this high risk period.

Poultry laying units should adopt the following preventative steps where appropriate:

  • Where appropriate, manure should be frequently removed from the site
  • Manure remaining on site should be managed to keep water content below 50 per cent, i.e. it is dry and friable. This may be achieved by monitoring water drinkers for leakage; preventing water ingress into the building; ensuring good ventilation of manure holding areas, and ensuring the livestock is healthy.
  • Certain feeds result in wetter litter, and the producer should take action to deal with constantly wet faeces.
  • Removal of manure/litter from the building and transport off site should comply with current Codes of Practice.
  • Broken eggs and fallen stock should be removed daily.
  • Cleaning up feed spillages daily, where possible. If this isn’t possible, the operator should monitor the spillage area more closely for flies.
  • Incorporating fly screening into buildings if possible and where it will not affect ventilation.
  • Training staff in monitoring and treating fly infestations.

Fly Prevention and Appropriate Measures for Pig Facilities

High risk times for fly infestation are prolonged periods of warm weather. Pig facilities should follow the steps below to help prevent fly problems:

  • Twice-weekly monitoring of adult and larval flies during April to October using appropriate monitoring methods.
  • Manure should be removed frequently, ideally daily (or as frequently as possible) from high risk areas such as finisher units.
  • Transport of manure/litter off site should comply with current local authority and Defra Codes of Practice.
  • Fallen stock should be removed daily.
  • Incorporating fly screening into buildings where possible and where it won’t affect ventilation.
  • Training staff in monitoring and treating fly infestations.
  • Clean feed spillages daily, where possible. If this is impossible, operators should monitor the spillage area more closely for flies.

Manure Removal and Transportation

To minimise the impact of fly dispersal during manure transportation off-site, operators should comply with relevant local authority and Defra Codes of Practice, especially:

  • Ensure adult fly numbers are minimised before houses are opened up for manure removal.
  • Avoid overloading trailers to prevent manure spillages onto the highway.
  • Cover trailers, if practical, when moving through residential areas.
  • Ensure that the recipient of manure has selected an appropriate location for the heap (see below), and where possible can cover the manure heap at the end of each day.
  • Wherever possible deliver infested manure to arable land where it can be immediately incorporated as it's spread.
  • Infested manure is unlikely to be suitable for reprocessing (for example as poultry manure fertiliser).

Storage and Spreading of Manure and Other Biosolids

It may be necessary to store manure or other biosolids before land becomes available for spreading. Manure has the highest risk of infestation, but other biosolids such as anaerobic digestor sludge can also become infested. Such storage should comply with relevant local authority and Defra Codes of Practice to minimise any potential fly nuisance during storage and spreading, as well as to prevent damage to land and watercourses.
Key points are:

  • Only non-infested manure should be applied to grassland or growing crops. Infested manure spread to bare soils should be incorporated by deep inversion ploughing at the time it is applied, or in any case within 24 hours.
  • Ideally, manure heaps should be located at least 500m distant from sensitive receptors where there is a known fly problem. Greater distances may be prudent where large quantities are being stored.
  • If there is a risk of fly infestation, field-stored manure heaps should be tightly covered with polythene sheeting or similar impervious material. There should be no gaps between overlapping sheets, and the edges of the sheeting should be buried in a 30cm deep trench around the entire heap and back-filled with soil.
  • Sheeting should remain in place for at least 10 days to ensure the death of any flies within the manure, and ideally longer to prevent re-infestation.
  • The integrity of the sheeting should be checked at least weekly, and repairs carried out as necessary.
  • Spreading should not be carried out on Bank Holidays or Sundays.
  • Manure should not be spread to land within three weeks of the last application of cyromazine larvicide. After spreading, the land should not be grazed or cropped for another 4 weeks.

Local authority Codes of Practice for manure removal, transport, storage and spreading emphasise that manure management is the joint responsibility of the producer, the transporter and the end user. There are steps that each can take to reduce and/or prevent fly infestations. These steps form an integrated approach involving good manure management, together with biological and/or chemical control methods.

Fly Prevention and Appropriate Measures for Waste Transfer Stations

High risk times for fly infestation at transfer stations are periods of warm weather. It is critical that proper fly control is used at the transfer sites with the flexibility to carry out additional treatments at peak times. This should prevent, or at least minimise, the potential for infestations of maggots/flies getting to landfill where it’s often too late to implement adequate control measures. Operators can do this by:

  • Monitoring adult fly numbers twice-a-week during April-Oct using an appropriate technique, such as resting counts in squares marked out on internal walls.
  • Carrying out waste acceptance checks (monitoring at weighbridge where possible, monitoring fly numbers in each load, recording heavily infested loads in fly contaminated load log sheet, treating loads and priority removal off site, not accepting fly infested loads from other waste sites). Where it's not always possible to monitor loads at the weighbridge, operators should monitor upon discharge.
  • Rejecting infested/problematic waste (what procedure is in place to ensure repeat problematic loads/known problematic waste streams are not accepted).
  • Proper waste handling and rotation (A/B system of waste in one day and out the next, waste not stored for longer than 48 hours, waste treated). This is especially important during the warmer months.
  • Ensuring that waste doesn't accumulate in inaccessible areas such as behind push walls, under plant or in corners. Any such waste should be removed daily, especially during the summer. Operators should also maintain good housekeeping, including cleaning down and disinfecting, regularly removing leachate and maintaining drainage systems.
  • Aiming to ensure contingencies are in place if the main nominated disposal point is unavailable e.g. technical problem at waste to energy site or high winds closing landfill. Contingencies should include identifying alternative outlets.
  • Minimising the time external doors are left open during the warmer months, and where possible installing automatic doors. Screen other openings where possible to reduce fly dispersal.
  • Training staff in using fly spray, identifying flies, toolbox talks and understanding the importance of monitoring/recording fly infested loads.

Fly Control Measures

Even if proactive fly prevention measures are in place, it is likely that some flies will still occur and need to be controlled. The following sections outline the various measures available. Under the COSHH Regs operators must consider non-chemical techniques first.

Figure 5. Carcinops pumilio feeding on housefly eggs

Biological Control of Houseflies

Naturally occurring predators

Within manure in poultry houses, there are often a number of housefly predators present naturally. These include the small mite Macrocheles muscaedomesticae which preys on fly eggs, the beetle Carcinops pumilio which feeds on housefly eggs and larvae, and Staphylinid beetles.

These predators are typically slower developing than houseflies. Predator numbers therefore tend to be low in the early months of the flock, but increase towards the end of the flock. They are more common in drier manure.

Introduced predators or parasites

There are a number of commercial suppliers (often veterinary practices) of other predators and parasites. These insects are delivered to the site, and released into the premises. Several releases may be required over the season. The main kinds available are:

  • Parasitic wasps (e.g. Spalangia and Muscidifurax) locate fly pupae, lay eggs into the case, and the developing wasp larvae eventually kill the fly.
  • The predatory larvae of some flies (e.g. Hydrotaea aenescens) prey directly on housefly larvae.

Physical Fly Control Techniques: Electronic Fly Killers and Traps

Flies within buildings may be caught by mass trapping with adhesive papers, or with electronic fly control units. These can be effective at reducing the numbers of flies present in small premises but several may be required throughout egg packing rooms or within waste handling buildings. They are unlikely to actually control infestations.

Figure 6. Electronic fly killer

Outdoors, liquid baited fly traps (Figure 7) are widely used in residents' gardens, for example.

Figure 7. Liquid baited fly trap

These traps are suitable for
More effective with smaller fly numbers in smaller enclosed areas, e.g. egg packing room, office, etc.

Catch a broad range of species.

Will not provide a useful level of control in large structures such as poultry houses or transfer stations, or in the open air.

Bag traps cannot be used indoors owing to odour.
May actually attract flies to the immediate area.


The approval process is administered by the Health and Safety Executive (HSE.) Approved products carry Statutory Conditions of Use on their label, which must be followed. These conditions cover dosages, application techniques, treatment frequencies, premises, target pests, and other issues. Where insecticides are being used at a site, the officer should check that products are being used in accordance with statutory label conditions.

HSE requires that anyone using pesticides professionally should have adequate instruction, training and guidance in their correct use. Although pest control can be carried out by appropriately trained in-house staff, in general such staff lack broader experience of pest control issues.

Pest control companies that are members of a recognised trade association, such as the British Pest Control Association, will typically have a broader experience, and meet minimum requirements in terms of training, insurance, pesticide handling etc.

Individual pest control technicians should have the RSPH/BPCA Level 2 Pest Control qualification as a minimum. In terms of the company’s experience of fly management, there are no specific qualifications on this, and the operator will need to ascertain their experience.

The COSHH Regulations 2002 require that all activities surrounding the use of pesticides (storage, use and disposal) should be documented, and records kept for at least three years.

Insecticides for fly control are available for various types of usage, as outlined below:

Insecticide space treatment (‘knock-down’ sprays)

Figure 8. Thermal fogging at a green waste composting site

Some insecticides are approved for use as space sprays, where the liquid insecticide is atomised into very fine droplets that drift in the air and contact flying insects directly.

Space treatment is typically achieved by:

  • Using a thermal fogging machine, which produces a dense white fog.
  • Using an Ultra Low Volume (ULV) sprayer, which uses an air-blast to produce the fine spray. The spray is less visible than that from a fogger. Such machines may be hand-held, or permanently installed, for example within a waste transfer station. ULV treatments are typically more effective than thermal fogging.

Space treatment insecticide products typically contain non-residual pyrethroids, which have a short-lived effect. See product labels for specific usage details, but typically treated premises should remain closed for at least 30 minutes after treatment, and should not be re-entered by unprotected personnel for two to three hours after treatment. Treatments are normally applied at the end of the working day. These systems are most effective when they are applied direct to insects.

Note: composters in the Association of Organics Recycling (AfOR) Scheme who wish to use fly control products, disinfectants and additives need to first complete an application form for approval.

Residual insecticide sprays

Figure 9. Applying residual insecticide for fly control

Some insecticides are intended for use as a residual spray and are applied to surfaces using a hand-held compression or pneumatic sprayer. They leave a deposit that remains active for some days or weeks. Flies that subsequently alight on the treated surface pick up a lethal dose of the insecticide and are killed. They typically contain residual pyrethroids or a carbamate. If operators turn or agitate the mateiral they’ll need to reapply the insecticide.

Insecticide baits

Insecticide baits typically consist of a mixture of insecticide, sugar and pheromone attractants. They are most commonly mixed to a paste and painted onto sheets of cardboard which are nailed up within the premises, or painted directly onto structural surfaces such as supporting posts, where flies commonly rest. Once applied, the bait will normally last some weeks or longer, but may need re-applying where large numbers of flies are present.

Figure 10. Preparing insecticide fly bait cards

Although originally developed for fly control in livestock units, some products are also now labelled for use in waste sites.


Larvicides are intended to control only the fly larvae, and have no useful effect on the pupal or adult stages. They are applied directly to the larval habitat, i.e. manure, or where the label permits, to refuse. They are normally applied as a spray, but one product may also be applied as dry granules to very wet slurry.

They are more effective on the younger larvae than older larvae, so treatment should be carefully timed on the basis of monitoring data. Cyromazine is more active on common houseflies than on lesser houseflies. Larvicides are relatively slow in action, with effects not becoming apparent until a week or two after treatment. Cyromazine is selective in action, controlling the fly larvae while leaving beneficial non-dipteran insects (beetles, mites, wasps) unharmed.

Larvicides are widely and effectively used in livestock units. They are typically applied either as a blanket spray to all the manure within a poultry shed, or as a spot treatment to wet areas or to other localised breeding areas identified through monitoring.

The label for cyromazine is relatively restrictive to delay the onset of resistance. It permits only two full treatments of manure within a poultry house, in the life of each flock of poultry. In addition, for common houseflies (but not for lesser housefly), each of the two treatments may be sub-divided into a series of nine separate more dilute treatments.

Some larvicides are also approved for use on waste. However, as these are slow acting products, their impact at most waste sites is limited. At transfer stations any treated refuse has normally left the premises before the product has had a chance to work, and at landfill sites any treated waste is buried and covered before the product has had a chance to work. It's only at premises where waste remains exposed and unprocessed for extended periods (a situation that should be avoided), that they may have a role.

Insecticide Resistance

Through the gradual process of mutation and then natural selection of advantageous genes, many insect pests have become resistant to insecticides.

Houseflies in particular, because they have a relatively short generation time, and because they are often the target of insecticide treatment, have become resistant to many of the insecticides used against them.

Resistance to a particular insecticide does not necessarily mean the insecticide is completely ineffective. Resistant flies can be managed by:

  • Prioritising the use of non-chemical control measures, e.g. manure drying, encouraging predators, swift waste removal, daily use of inert cover, etc.
  • Complying with all insecticide product label conditions, particularly those intended to delay the onset of resistance.
  • Alternating the use of insecticide products containing active substances with different modes of action.
  • Minimising treatment practices (e.g. regular residual treatments) that are known to accentuate resistance problems.

June 2013

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