Council steps up fight against pesky midges

Efforts are being stepped up to rid the Bromley oxidation ponds of midges ahead of the warm summer months.

The midges, which breed well in the shallow, warm waters of the oxidation ponds, have been causing problems for residents living nearby because of their sheer numbers.

Contractors dose the oxidation ponds with methoprene pellets.

Traditionally Christchurch City Council has relied on chemical dosing alone to try and control the midges, but this year it is taking a multi-pronged approach to try and reduce the midge population.

“We know the midges are an unwanted nuisance and we are working hard to bring the numbers down so they cause less of a problem for nearby residents,’’ says Adam Twose, Council 's Manager Operations Water and Wastewater.

“Unfortunately the oxidation ponds are the perfect breeding ground for midges but we are dosing the ponds every two weeks with slow-release methoprene pellets that will prevent the larvae from developing into adults.

“Methoprene is commonly found in flea treatments for dogs and cats and in home insect sprays. It is not very toxic, except to midges and fleas, and it won’t significantly impact on the bird or water life in the ponds . Typically it does keep the midge numbers lower than if we weren't dosing,’’ Mr Twose says.

“This year we are also trying something new by applying a contact insecticide on the vegetation around the ponds which should act in the same way as domestic long-lasting surface fly sprays. Again it has a low toxicity and shouldn’t cause any unintended harm.’’

Mr Twose says the Council is also proposing vegetation screen planting to reduce the light from nearby residential areas - midges are attracted to light - and trialing the use of UV traps.

“We’re also looking at whether we have enough capacity at the treatment plant to be able to reduce the number of ponds so there are fewer areas for the midges to spawn. However, we do need the oxidation pond volume and area to provide the necessary treatment of the wastewater.

“Another control technique we are investigating is sun baking. This is where we drain the ponds of water in turn and leave them to dry out, which we believe should kil the midge larvae and help reduce the number of adults emerging.’’

Mr Twose says a robust monitoring programme is in the process of being implemented to monitor the midge numbers so the Council can see if its control techniques are working.

“Some of the techniques we are proposing are long term, like the vegetation planting, so we're not going to get rid of the midges overnight, but hopefully we still start to see their numbers decline,’’ he says.

The oxidation ponds are an ideal breeding ground for midges.