While mosquitoes can be controlled around farmsteads to reduce the dangers of West Nile transmission, treatment of farmland is not
advised.
The three prairie provinces will see little insecticide application aimed at the rural population of Culex tarsalis mosquito, the insect known to transmit the West Nile virus to humans and horses.
“Where the heck would you begin,” said Ken Engel of the Saskatchewan Association of Rural Municipalities.
“It is a big area with a little population, so when it comes to control, we expect to see few efforts or programs outside of hamlets or semi-urban areas in rural municipalities.”
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Phil Curry of Saskatchewan Health agreed with Engel’s assessment.
“Farms are small islands in a sea of mosquito habitat. It is often not practical or cost effective to start a larviciding or adulticiding program around a farm,” said Curry.
Joel Kettner, chief medical officer for the province of Manitoba said “like anybody, farmers should begin with habitat source reduction and personal protection with appropriate clothing and repellents.
“The problem with farms is that they are very large and very diverse and the mosquitoes need only a tiny habitat in which to breed.”
Kettner said for that reason the government is not recommending that individuals use insecticides.
The three officials agreed that individual producers do have options. In areas where drainage is not possible, such as livestock watering and irrigation areas, targeted products such as the bacterial larvicide BT-i, or bacillus thuringiensis isrealiensis, are best. The product is also known as Aquabac, in smaller quantities, or Vectobac in a commercial or agricultural formulation.
Knowing the enemy is important, said Saskatchewan’s provincial entomologist, Scott Hartley.
“BT-i is safest because it attacks only winged flies. It is a larvicide that works on water that is shallow and stagnant. It only works on the mosquito at the larval stage though, so producers first have to determine if they have the larvae to kill,” said Hartley.
“The downside is that it has a very short residual effect, only about 48 hours. Then, if you missed a population for some reason, you need to reapply,” he said.
“The (Culex) tarsalis will breed well in hoofprints around cattle waterers. It is a tough adversary.”
Trish Dowling, veterinary researcher and professor at the University of Saskatchewan, said the insect is “a tenacious feeder that seems to become more voracious as the season wears on. She wants those last big blood meals so she can lay more eggs before the frost arrives.”
This behaviour coincides with the highest levels of West Nile infection in the bird population in late July and August.
“And that is when you need the most control or protection from the insect.”
Curry said producers also have the option of using other insecticides such as chlorpyrifos (Dursban) or malathion as larvicides but it is highly toxic to fish and other aquatic organisms and should be used only in temporary pools.
“The problem with these is they kill everything in the water, including the aquatic predators (of the mosquito),” he said.
Hartley said farmers can’t apply larvicides to water bodies that flow from their property, such as drainage ditches.
“But if you are successful in controlling the tarsalis, it only will travel two or three kilometres at most, so you will have likely had good control,” Hartley said.
Propane-powered foggers can be bought or rented and used to control the adult insect with propoxur, malathion or synthetic pyrethrins, but entomologists say the most effective control is always at the larval stage.
Alberta’s provincial veterinarian, Gerald Ollis, said his province will be offering advice, but no money to rural municipalities for mosquito control.
He said the need for mosquito control will be limited, because the West Nile threat has only just arrived in that province.
All three prairie provinces request that farmers contact them if they have dead birds including crows, magpies, ravens and jays, or if they have West Nile symptoms in horses.
In Alberta, call 310-0000 or 780-427-3448.
In Manitoba, call 788-8200 or 888-315-9257.
In Saskatchewan, call local municipal offices.
