How Do I Prevent My Garden From Spreading Mosquito-Borne Diseases?

terrestrial bromeliads don't harbour mosquitoes

terrestrial bromeliads, like this pineapple, don’t harbour mosquitoes

Is gardening fashion fanning ill health?

Cairns City Council has increased on-the-spot fines for homeowners found to have mosquitoes breeding on their property to $400. John Pilspanen, of Queensland Health, says the disease will keep spreading until everyone takes the necessary precautions.

Queensland Health is concerned about the increasing infection rate of the current dengue fever outbreak in far north Queensland. Described by a Public Health physician as “the most rapidly spreading outbreak”, forty staff are involved in mosquito control work.

“What it’s going to take is for people to get out in their backyard and clean up their backyards to eliminate the breeding from their own site and their own backyards to protect themselves?”, Pilspanen said.

Recent flooding has helped trigger mosquito breeding, ideal conditions for making a dengue epidemic more likely. It takes just three to four days for a mosquito to reach adulthood.

The landscaping fashion of using small water features has further added to the range and number of opportunities for mosquitoes to breed in our suburbs.

Hiding there in full view is one garden accessory that might escape the mosquito-wise homeowner, tourist resort or commercial landscape: bromeliads.

As new residential suburbs weave their footprints ever outwards, with them come bromeliads, courtesy of the world’s most widespread ecosystem engineer – the gardener.

Sprouting along tree branches, perched atop hanging baskets, framing formal gateways, and filling borders, these lavish, long flowering South American plants are perfectly suited to the tropics and subtropics.

Equally at home growing in trees and in the soil, most of the bromeliads we grow have a central rosette of leaves designed to capture rainwater, storing it in a mini-pond. This self-watering adaptation keeps them well hydrated in dry weather, and creates an ideal micro-habitat for small aquatic creatures. In South America fish and tree frogs hunt and breed in them, and birds and honeybees drink from them. And along with a myriad of microscopic organisms you’ll discover mosquitoes.

Bromeliads are beautiful. I adore the richly coloured and vividly patterned foliage of Neoregelia. I love seeing boldly flowering Guzmania used dramatically in ornamental landscapes. It’s fascinating observing the little flowers of Aechmea rising up through the water held by their own tanks, resembling miniature waterlilies. And who is not struck by the beauty of stately Alcantaria growing either side of an entrance, their flower heads filled with fluffy seeds?

We also know what it’s like hanging around specialist bromeliad displays in gardens and nurseries – you always get bitten by mosquitoes. Mosquito repellent is a must if you’re planning to linger (or film) in a garden where they are growing in quantity.

I grow tank bromeliads in my garden. Six favourite, easycare versions of tank bromeliad. To limit mosquito breeding, mosquito bites and water use, I grow a modest number of each.

I’ve written to Cairns City Council and the local press and I work with a media spokesperson for Queensland Health, so I also put these questions to Linda:

* Have Queensland Health and Cairns City Council quantified the number of backyard tank bromeliads that exist in dengue-fever zone gardens?

* How do they inspect and assess properties growing them?

* How significant a public health risk do officials believe tank bromeliads pose, and are they doing their best to manage the risk posed by their cultivation?

I got no replies, so what can a responsible gardener do?

What can I do to help control the spread of mosquito-borne diseases?

Apart from dengue, mosquitoes spread West Nile virus, Murray Valley encephalitis, Ross River virus and several other nasty diseases. Plus there’s the ever-present risk that malaria-transmitting mosquitoes will jump the 5 km gap separating New Guinea from Australia.

A biological larvicide, containing Bacillus sphaericus, is used by authorities to control mosquitoes in the wider landscape.

A chemical larval growth regulator containing S-Methoprene can also be sprayed by pest controllers over smaller areas – possibly including tank bromeliads used at ground level.

Gardeners in the dengue fever zone should:

  • Inspect and repair poorly draining level roofs, unblock gutters, and empty buckets and saucers used under potted plants. Gather fallen palm fronds, which can gather water. All are perfect mosquito nurseries;
  • Be a good steward. Inspect and ensure that all entry points to your rainwater tank are fitted with mosquito-proof netting. Proofing should also be capable of excluding frogs and lizards, which may introduce salmonella into tank water.
  • Stock water features with mosquito larvae-devouring fish. Pacific Blue Eyes are tiny fish, happily surviving in bowls and pools, and are a very effective and non-invasive native species suited to mosquito control.
  • Substitute tank bromeliads for other species. There are ground dwelling (aka terrestrial) species that do not have tanks, like pineapples, and there are ornamental pineapple cultivars with pretty foliage and flowers as well as the well-known culinary cultivars. There are also many dry climate-adapted, ground dwelling bromeliads which don’t have tanks.

Think substitution. These bromeliads don’t hold water and need less frequent irrigation. These include a very wide range of Tillandsia, like Old Man’s Beard (Tillandsia usneoides). I grow Tillandsia pyramidata in pots, baskets and as a ground cover. Another old favourite is Queen’s Tears (Billbergia nutans), also a great, winter flowering ground cover.

Less well known, but equally attractive kinds such as Canistropisis burchellii, a cute little plant for pots, and hybrids and species belonging to the genera Dyckia, Ochagavia and Puya (pronounced p-wee-ya). I grow these, plus a range of pineapples.

If you really want bromeliads but live in a dengue area, a good gardener can have their cake and eat it too. Shop consciously, not impulsively. And take mosquito repellent while you shop.

Further reading: the NSW Arbovirus Surveillance & Mosquito Monitoring Programme.

Reference: Concerns grow as Cairns dengue outbreak spreads, ABC News On Line, 24.2.09

Jerry Coleby-Williams
24th February 2009