First step is to make sure these are voles. Voles typically make many (!) small (<2" diameter) holes that don't have dirt mounds associated with them. 
Yes, there are toxic baits you can put in burrows but again, must be certain of what species you're trying to control (the product label is the law)  and the most effective poison (ZincPhosphide) is 1)registered and restricted to purchase and use by licensed pesticide applicators 2)is non-specific and kills whatever ingests it and 3)is apparently losing its effectiveness via behavioral avoidance by voles. There are other over the counter/retail products, but exclusion (e.g., hardware cloth beneath raised bed boxes) and trapping (mouse traps with wide "cheese" paddle placed at burrow entrance such that animal will run across the paddle, not "into" it) are the best bets for yard-scale management. 
Feel free to return here and upload photos (with an item to scale size) if you'd like help with species ID.