Which of the following is generally not an effective control method for voles?

Fumigants are not typically effective for controlling voles because these rodents live in burrows or underground tunnels, where fumigants may not adequately reach them. Fumigation is more effective for pests that are exposed or in areas with little obstruction. Since voles create extensive tunnel systems, getting the gas distributed effectively throughout their habitats can be challenging, often resulting in poor control.

In contrast, toxicants, anticoagulants, and baited snap traps are all methods that can directly target voles. Toxicants provide a means of poison that voles can consume, while anticoagulants work by affecting the blood's ability to clot, leading to the eventual death of the rodent. Baited snap traps are physical traps designed to kill voles quickly when they attempt to access the bait. Each of these methods has direct effectiveness against voles, making them more suitable choices compared to fumigants.