There has been limited, if any, economic loss to Canadian farmers due to restrictions on the use of strychnine based rodenticides for the following reasons: strychnine based poisons are available to licensed applicators; anti-coagulants are readily available; strychnine poison alone is not an effective control measure; and an integrated strategy for controlling pocket gophers is recommended and is the most effective method.
Each province has regulations for the use of strychnine. In Saskatchewan, for example, the sale of strychnine is restricted to pest control operators, farmers and persons authorized in government approved pest control programs where the vendor maintains a record of sales including the name, address and signature of the purchaser along with the quantity of product purchased. The vendor, who in this case is Saskatchewan Association of Rural Municipalities, may have further restrictions.
The annual losses in yield reductions and equipment breakdown from pocket gophers for the province of Alberta has been estimated at $14 million to $30 million annually. For the province of Manitoba losses are estimated at $15 million annually. No published data could be located for economic losses Canada-wide. In 1997, 3.5 million to 5 million hectares of forage, primarily alfalfa, in western Canada was infested with pocket gophers. The reductions in productivity and damage to equipment are significant and control is necessary.
Control of pocket gophers requires an integrated approach. There are various types of control methods to reduce pocket gopher populations. Control methods include trapping, gassing, flooding, exclusion, encouraging natural enemies, and poisoning. Trapping has proven to be an extremely effective control but is labour intensive and is limited in the area one can control. Physical control can include removing the food source, using pets to discourage entrance into a yard, and noises, disturbing noise placed in the burrow. Buffer zones are effective in isolating certain areas from pocket gophers. An example of a buffer could include spraying the surrounding area with a broadleaf herbicide which would eliminate the pocket gopher's food source. Natural predators such as owls and snakes will assist in control of pocket gophers, providing their existence is promoted and encouraged.
There are three types of rodenticides available on the market to control pocket gophers: strychnine based, zinc phosphide based and anti-coagulants. Strychnine and zinc phosphide are both restricted and generally limited to use by licensed pesticide applicators. Anti-coagulants are readily available to everyone. Pocket gophers are very sensitive to the taste of poisons and readily reject or limit intake of many poisons. They also have an ability to metabolize certain amounts of these poisons and there have been reports of resistance to poisons if provided in sub-lethal doses. Field studies have shown that using strychnine or zinc phosphide based poisons controlled 35% or less of treated pocket gopher populations.
The recommended method of controlling pocket gophers is called a border control strategy. This is used on fields which were seeded in the last three years. This strategy requires the trapping of gophers in the center of the field—new fields are recommended as populations of gophers are low—and setting up permanent control around the perimeter of the field using traps alone or a combination of traps and bait set in existing burrows. This strategy prevents pocket gophers from entering a clean field.