Considerations Related to Richardsons Ground Squirrel (Spermophilus richardsonii) Control in Montana

Alfalfa (Medicago sativa L.) production is limited in Montana due to activities associated with Richardsonʹs ground squirrels (Spermophilus richardsonii), and control is often considered to be cost prohibitive. This study was conducted to document the economic impact of ground squirrel activities on alfalfa yield and demonstrate field efficacy of available toxicants. Montana alfalfa producers completed a survey to determine perceived severity and losses due to ground squirrels. Actual first-harvest forage yield losses were determined at two locations in southwest Montana in 2003 and 2004 using cage exclosures. Chlorophacinone (Rozol), diphacinone (Ramik-Green), and zinc phosphide were administered at two locations to determine the efficacy of each treatment. Survey results across Montana indicate alfalfa producers estimate a 24% average reduction in forage yield in areas known to be infested with ground squirrels. First-cut forage yields were reduced by 31% in southwest Montana. Rozol was the most effective control agent (84% efficacy) while Ramik-Green was the least effective control agent in our trials (29% efficacy). Landowner perceptions of ground squirrel damage are similar to actual yield reduction and possibly underestimated. The costs associated with the control of ground squirrels can be quite high, and caution must be exercised when implementing a new control program to assure these costs are offset by forage gained.