Flies: Gain control before they impact productivity on-farm

Flies are not only an irritant for cows and farmers alike, they also affect cow productivity – reducing how much animals graze and therefore affecting milk yields and growth rates, as well as behaviour in the milking parlour.

By the time you notice cattle or sheep troubled by flies, a population explosion is already taking place. However, it’s easy and cheap to make some fly traps, and then keep an eye on them every few days for an early warning that fly numbers are on the rise.

You need to choose suitable bait for the flies you wish to trap; for example offal, such as raw liver, is suitable bait for the fly species that bother livestock.

As soon as you start seeing flies in the trap, then you know they are going to be bothering stock and you will need to take appropriate action.

How to make a fly trap?

Take a two-litre plastic bottle and cut the top third of the bottle off;
Make some small holes in the end of the plastic bottle in order to allow rainwater to escape;
Invert the top of the bottle into the remainder of the two-litre bottle and seal it with clips/paper clamps to fasten it in place;
Place the bait, which can be made up of dog food, or an offal-based product in the bottom of the bottle;
Hang the bottle on a fence or gate post by fixing string to the paper clamps attached to the bottle.

flies - DIY fly trap diagram — Creating a DIY fly trap

When to start with fly control?

If you wait until fly populations are already established and then try to tackle them, you’re unlikely to win the battle. An early start to controlling insects around livestock gives the best chance of minimising the annual population explosion of flies and midges that begins as soon as average daytime temperatures reach 10°C (below).

flies - graph showing increase in population of various fly breeds by month — Increase in population of different flies

Winter frosts can help reduce the coming summer’s insect populations. However, even if air temperatures are below zero for several days running, the larvae of some species relevant to livestock typically survive over winter about 10cm below the soil surface where frost may not penetrate, so this cannot be relied upon to kill insect larvae.

Moreover, larvae of some species survive over winter in woodland litter, where frost penetration is quite rare no matter how cold the weather. Then as soon as they hatch from pasture or woodland, blood-sucking species can migrate several kilometres to find livestock on which to feed on.

While farmers cannot eliminate insect breeding sites from pasture and woodland, a meaningful impact around farm buildings is possible by minimising open dung heaps, slurry puddles, and old hay and straw stacks.

For maximum control, action must start before the insect breeding season; waiting until insects are bothering livestock allows breeding populations to become established and difficult to get on top of.

Welfare impact of poor fly control

Flies don’t only annoy cattle and sheep; they can cause major economic production losses through reduced feed intake which impacts productivity. Studies in cattle have shown the production loss caused by flies can be up to 0.3kg/day growth rate loss and up to 0.5L/day in milk loss.

Flies attack and feed on cattle and other animals. This causes irritation and can be involved in the transmission of diseases such as pink eye and summer mastitis.

Midges also spread viruses that cause diseases such as Bluetongue and Schmallenberg. Blowflies are important due to the damage caused by their maggot stages.

Treatment

In conjunction with good farmstead hygiene, residual pour-on pyrethroid treatments such as deltamethrin (e.g. Fly and Lice Spot On) are licensed to control insects for up to eight weeks, depending on species and population.

To keep nuisance flies at bay Fly and Lice Spot On should be used monthly in cattle. There is a zero milk withhold period and so Spot On can be used in pregnant and lactating dairy cows.

In sheep, it is licensed to treat established blowfly strike and a single application directly onto the maggot infested area as soon as fly strike is seen, will ensure blowfly larvae are killed rapidly.

In the case of more advanced strike lesions it is advisable to clip out the stained wool before the treatment is applied. The active ingredient has proven activity against midges.

Alternatively, in cattle, a long acting cypermethrin (Flectron Fly Tags) is available giving season-long fly control from a single tag. Flectron Fly Tags can control flies for up to four months.

For maximum benefit they should be applied at the beginning of the season and all animals in the herd should be tagged. Successful fly control starts now, so now is the time for farmers to engage with their prescriber and ensure plans are in place for the season.