If you are like me, you are plagued by mosquitoes in the garden. It is one thing to stay out of their way at dusk but it is quite another when the Asian Tiger attacks you all day long. Last year the mosquito population was so bad I could not go outside and I started to wonder if there was a better way. This spring, I contacted several companies to see if my property could be sprayed to prevent mosquitoes while not harming pollinators or my edibles. I don’t have a pond or pets but I have quite a lot of edible plants intermixed with other plants on the property. A lawn service mows the grass but I never know when the crew is coming. Plus, I knew I would not always be at home to let the pesticide applicator know where the edibles were in the garden nor would I be able to inform the lawn service crew when and if the place was just sprayed with a pesticide. All of these factors made it complex for me to figure out how to control mosquitoes but fortunately I was able to attend a free presentation at a local library. Kirsten Conrad Buhls, Extension Agent, Virginia Cooperative Extension, Arlington County, gave an excellent Powerpoint presentation entitled “Gardening in the Time of Zika: Nuisance Mosquito Management.”
I learned that there are 40 mosquito species in Virginia in a variety of habitats but most are aquatic. Up until the mid-1980s, the most problematic species was Culex, which came out at dusk and fed at night. This species lives in the woods and prefers the type of stagnant water that usually does not occur near residential homes but they can also breed in “container water.” Container water is the fresh water that collects from rain and sits in pockets or depressions in objects or in containers.
After the mid-1980s, a Southeast Asian native arrived called the Asian Tiger mosquito, Aedes albopictus. The Asian Tiger is active during the day and prefers to breed in container water. The Asian Tiger has a cousin, Aedes aegypti, who also prefers to breed in container water. Both are vectors for transmitting diseases and both can transmit the Zika virus but A. aegypti is more effective and considered a primary transmitter. Both could prosper here in Virginia, as in we have the appropriate environmental conditions, but currently Virginia does not have a substantial A. aegypti population. At this time, Zika is not established in a population of mosquitoes in America.
Only females bite humans to get a “blood meal” before laying eggs. They are cold blooded so they don’t bite if the temperature is below 50 degrees but they can live as long as 2 to 3 months and adults that hibernate can live up to 8 months. This means that the problem is temporary; it exists only in the hot summer months.
Because they breed in container water which is common in residential areas, anything that collects water should be dumped after it rains. Mosquitoes require as little as one tablespoon of water to lay eggs and it can take as short a time as 3 days for a new generation. After it rains, either dump the water or eliminate the object (e.g., put watering cans back inside the tool shed or throw away old tires). Be aware of what can collect water such as open trash bins, pets’ water bowls, potted plant saucers, toys, buckets and barrels, and the corrugated gutters. If the water cannot be dumped, such as a pond, make sure the pond has plenty of mosquito larvae eating fish, dragonfly larva, frogs, toads, and other such organisms. For rain barrels, use the mosquito dunks that are made of a safe bacteria. Or transform the water feature so that the water is moving instead of still by installing a bubbler or waterfall. Mosquitoes do not like moving water or moving air.
Kirsten dispelled common myths: Bug Zappers are not effective killers of mosquitoes, bats do not prefer to eat mosquitos, and purple martins are not big mosquito eaters. Plants that are reputed to repel mosquitoes do not work if they are just sitting in the landscape; however, a dense groundcover such as English ivy can harbor adult mosquitoes. It does not matter what you eat but mosquitos are more attracted to big people and prefer men over women.
If you are going to garden, wear long sleeves, long pants, socks, and shoes, or spray yourself with repellants such as DEET (25-30 percent), Picaridin (20 percent), oil of eucalyptus, or IR-3535 (Merck 3535), which is found in Avon’s Skin So Soft. Spraying Listerine and using dryer sheets, VapoRub, or vanilla are not effective protection.
The most environmentally friendly effective control is to control the larva stage. Spraying the adult mosquitoes in the landscape should be the last resort and should be based on surveillance data. The most popular mosquito adulticide for home landscapes is permethrin but it is toxic to fish, aquatic arthropods, and the non-target insects (pollinators). Don’t be fooled when the pesticide applicators try to sell you on the fact that it is “natural” based on a chrysanthemum plant. What they are spraying is not natural, it is a chemical. There are substances called pyrethrins that are the active ingredients in pyrethrum, an extract of a flower, and these are are natural insecticides that act by blocking chemical signals at nerve junctions. However, commercial sprayers are not spraying pyrethrins. They are spraying permethrin, which is based on pyrethroids, synthetic pesticides. Permethrin is a pyrethroid insecticide that is light-stable and has a longer duration of activity against insects than pyrethrins. So what the company is selling and spraying on your garden is permethrin, a chemical that will kill aquatic life and pollinators and render vegetables, herbs, and fruits non-edible.
Mosquitoes have a flying range of 600 feet, about 1 to 2 miles. If your property is sprayed, it will kill the existing ones but the next day more can fly in. If you spray your garden and your neighbors don’t, you can always inherit your neighbors’ mosquitoes. Commercial companies may tell you that the spray last for a month but that does not prevent new mosquitoes from entering nor does the spray continue to kill for up to a month. In my mixed edible garden, only the grass could be sprayed which gets cut every few weeks. Since my grass gets cut by a service, I am concerned that the pesticide company will spray with a chemical one day and the lawn service crew will come and cut the grass the next day. I don’t know what harm that chemical would cause if the crew were to breath it in as they were cutting.
The presentation cleared up a lot of confusion and I decided not to have my garden sprayed. I will be more vigilant about dumping water on my property and educate the neighbors to do the same. I will try the oil of eucalyptus and I will cut back my English ivy as best I can. I will still garden in the cool morning with long sleeves and pants and then I will spend the hot afternoon writing about mosquito control in my air conditioned home.
To learn more about mosquito management, call the Arlington County Extension Office at (703) 228-6414 or visit the Master Gardeners of Northern Virginia website at http://www.mgnv.org. The website has a tab devoted to the subject that has several links to resources including the Powerpoint presentation. https://mgnv.org/zika-and-mosquito-control/