Mosquito Treatment in Portland, OR

What to look for

Mosquito development is a race between water and time. Adults lay on standing water, and the young need seven to ten days to reach flight. At summer highs averaging 81F, that runs toward the slower end, which is why populations here build gradually rather than exploding. Culex, the group tied to West Nile virus, uses water that has stood long enough to develop a film of organic matter, and it can travel as far as two miles from where it hatched, so a stormwater basin or a neglected pool blocks away can be part of your problem. Container specialists in the Aedes group work at a smaller scale, laying eggs on the dry inner walls of pots and buckets that stay viable for up to eight months, and staying within a few blocks their whole lives. Average humidity of 73 percent keeps adults comfortable once they emerge, which is why a modest number of mosquitoes here can be more annoying than the count suggests.

• 1Evening biting in July after weeks of dry weather with no rain to blame.
• 2Larvae visible at the surface of a rain barrel or a stock tank.
• 3Mosquitoes lifting out of ferns and low plantings when you weed.
• 4Standing water in the bottom of a rain garden more than four days after watering.
• 5Wrigglers in a pot saucer or a self watering planter reservoir.
• 6Biting concentrated around a garden pond with no pump or fish.
• 7Insects resting on the shaded north side of the house through the afternoon.

Treatment options and typical costs

Prices are typical published ranges. Ask what’s included before you compare quotes.

Why summer, not the rainy season, is the mosquito season in Portland.

Most of the 43 inches that fall on Portland arrive between October and May, when average temperatures are too low for larvae to develop quickly and adults are not flying. That water runs off, drains, or evaporates without producing much of anything. Then summer arrives, the sky shuts off, and the temperature finally supports development. At that point the only standing water left is water somebody is keeping: a barrel, a pond, a rain garden, an irrigation puddle, a saucer under a pot. That inversion is good news. In a city where rainfall drives breeding, you are fighting the weather. Here you are managing a short list of features you own. It also explains why biting peaks in July through September rather than in spring, and why a service plan sold as year round coverage is mostly selling you months in which nothing is happening. Ask what actually gets done in February before paying for it. The intuition that rain equals mosquitoes fails badly in this climate.

Rain gardens, barrels, and how to keep both.

Fine mesh over the downspout inlet and over the overflow outlet solves it completely, as long as the mesh is tight enough not to sag into the water. Scrub the inside when you drain it. A rain garden is fine when it works as intended, which means water infiltrating within a few days. If yours still has standing water on day six, the soil is not draining and it has become a pond, so either amend the design or treat the water. Ponds want either fish or a pump, since surface movement prevents egg laying. For everything you cannot screen or move, a bacterial larvicide handles the larvae while leaving the water usable for the garden it was collected for. The features that make a yard water wise are also the features that hold still water, and that tension is worth addressing directly rather than pretending it does not exist. A rain barrel is the clearest case. It is designed to store water for weeks, in shade, with organic debris washing in from the roof.

Where to look on a densely planted lot.

Start with intentional water: barrels, ponds, basins, birdbaths, a rain garden or swale. Then the irrigation side. In a dry summer, drip lines and sprinklers are the only thing keeping soil wet, and a sunken emitter or a broken head can hold a small puddle through the whole season without anyone noticing under mulch. Next, containers. Pot saucers are the classic, but self watering planters are worse, because the reservoir is designed to stay full and is hidden inside the pot. Then the low ground. Terraced and hillside lots are common in Portland, and each terrace has a flat spot where water stalls. Finally the odds and ends: a wheelbarrow, a tarp over stored furniture, a tire, a watering can left out. Because everything on this list is on your property, a thorough afternoon of looking usually ends the mystery entirely. Work from the largest volume down to the smallest, because that is the order in which they matter.

What should a first visit include?

What you want at the end is a written scope: which water gets larvicide and how often, which beds get residual product, how many visits are included, and which months the plan covers. In a four month season, a twelve month agreement deserves an explanation. And ask what happens if biting has not improved after two visits. The right answer involves looking again for a missed water source, not adding more product to the same beds. A useful first appointment is a walk through the garden with somebody who knows what water does, not a truck arriving to spray a perimeter. They should open the barrels and look inside. They should ask when the rain garden last held water and for how long. They should check pot reservoirs rather than glancing at pots. They should ask what time of day you get bitten, since evening biting in the open and daytime biting among containers lead to different work. They should look at the irrigation schedule, because in a dry summer that is the water supply.

Renters, landlords, and the wet back corner.

If you rent, handle your own containers first so the remaining problem is clearly structural, then send the drainage and gutter items with photos and dates. If you own rental property, one look at where water sits in July, plus screens on the barrels, heads off most of what tenants will complain about in August. On terraced lots, drainage problems repeat every year until the grade itself changes, so the one time fix pays back quickly. Sort responsibility by what is part of the property rather than by who is annoyed. Grading, drainage, gutters, downspouts, an installed pond, and the irrigation system are owner items, because addressing them is maintenance on the property itself. Barrels, pots, planters, and a birdbath belong to whoever brought them into the yard. The common dispute in this city is the chronically soggy corner. If a spot holds water for a week after every irrigation cycle, that is a drainage issue rather than a housekeeping issue, and treating it every month forever costs more than fixing it once.

How do you compare two mosquito quotes?

Dense beds mean a large resting surface, and two quotes can differ enormously here without either saying so out loud. Which months are covered? Local biting runs roughly June through September, so pay for that and question anything billed for the winter. Then ask what is excluded. Drainage correction and gutter clearing usually are, and on a lot with a chronically wet corner that is the piece that actually ends the problem rather than managing it. Set price aside and compare four things, because these proposals are rarely equivalent. What water did they identify? On a garden lot, a pro who inspected properly can name your barrel, your pond, or your rain garden without prompting. If the quote only describes spraying, nobody looked. Is larvicide included, and on what interval? Water you are keeping needs treating every three to four weeks, and that is separate from anything applied to foliage. How much planting gets treated?

Simple ways to keep mosquitoes away

• Screen rain barrel inlets and overflows with fine mesh, and check the mesh monthly.
• Confirm a rain garden or swale drains within three or four days after filling.
• Empty and scrub pot saucers and self watering reservoirs once a week in summer.
• Add a pump or fountain head so pond and basin surfaces never sit still.
• Clear gutters in autumn so winter rain does not pond behind leaf litter.
• Turn buckets, wheelbarrows, and bins upside down between uses.
• Thin dense low planting on the shaded side so the soil dries between waterings.
• Repair torn screens before the June population begins to build.

Questions people ask

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