MAFRI Organic Agriculture Specialist
West Nile Virus (WNV) is a mosquito-vectored disease which can be serious and sometimes fatal. Humans can become infected with the virus if they are bitten by mosquitoes that have previously bitten an infected bird. Most mosquito species do not pose a significant risk of transmitting WNV. The main vector of the virus in Manitoba is the adult Culex tarsalis mosquito, which takes blood from either birds or mammals. Fortunately, C. tarsalis mosquitoes occur in much smaller numbers than many of the other commonly occurring nuisance mosquito species found in Manitoba. Adult mosquito traps around the province have been indicating low numbers of C. tarsalis up to mid-July.
In most cases, people who are bitten by an infected mosquito do not become ill. Of those who do become ill, most will experience flu-like symptoms such as fever, headache and body aches. In Manitoba, the risk of people contracting WNV is low (less than one in 10,000).
Manitoba Health is responsible for coordinating the activities of the WNV program in Manitoba, the goal of which is to assess risk and take appropriate measures to limit the negative impact to human health. They are also aware of the impact that control programs may have on the organic and beekeeping industries.
Larviciding is generally considered the first option in mosquito control intervention. A Bacillus thuringiensis (Bt) product is normally used for larviciding in the early part of the season. Adulticiding is the second option in mosquito control, where a synthetic insecticide is used to control the adult stage of the mosquito. This is an issue of concern for organic producers.
Municipalities normally have the choice of whether to undertake mosquito control measures or not. Many will comply with buffer zones around organic properties if notified well in advance of spraying for nuisance mosquitoes, including the City of Winnipeg. However, if public health is threatened, a Health Order can be issued by the province for control measures in certain areas targeted at C. tarsalis. In this case, buffer zones will not be considered. At the present time, Manitoba Health has stated that only ground applications (usually from roads) will be used in 2011 and that aerial applications are not planned. The fogging applicator disperses a treatment for about 90 metres.
Be aware, be informed!
All organic producers are urged to be aware of any adulticiding activities in their areas. Keep in close contact with your municipal office. Some RM offices maintain a contact list of organic and bee producers. Adulticiding depends on trap counts and is often done on very short notice. Generally, control measures will occur within town limits of larger communities (population of 1000 or higher) and up to about 3 km beyond, but if the mosquito numbers warrant, virtually any community may be applied with adulticide.
Remember that a minimum buffer of 25 feet (8 metres) is required between an organic field and an area treated with a synthetic pesticide. Any production from that area is considered conventional for a full three years. Hopefully the mosquito spraying won’t affect anyone in this manner, but organic producers must be aware of the consequences if it does happen. Manitoba Health is concerned with the risks of WNV to human health, so they are prepared to do whatever is best for “the common good”, but in the past they have made efforts to reduce the potential impact that control measures would have on organic and bee operations.
- For more information about Manitoba’s WNV program, visit the Manitoba Health website at http://www.gov.mb.ca/health/wnv/ or phone 204-788-6795.
- Health Links at 204-788-8200 or toll-free 1-888-315-9257 also has good WNV information.
- City of Winnipeg BUGLINE at 311 (Wpg. area) or toll-free 1-877-311-4974 http://winnipeg.ca/cms/bugline/