Mid-Season Gopher Control

By James Tansey PhD, AAg, Provincial Insect and Vertebrate Pest Management Specialist and Faith Hillsden, Survey Tech Summer Student

July 2024

Richardson’s ground squirrel (RGS) populations have been high in some regions and growers are trying to cope with damage to seedling crops, especially canola. Re-seeding has been required in some cases.

The best time to control RGS is in the spring as they emerge from overwintering and have few options for food. Once the juveniles come up, and litters are typically five to eight young, populations boom and damage can increase dramatically. Because of alternate food sources, control with baits at this time of year can be very challenging. Once summer comes and the juveniles emerge, control becomes much more difficult. RGS are much less likely to take poison baits with a variety of palatable food sources around. Shooting can have a local effect but is labour intensive and, since young males are being driven away from maternal burrows at this time of year, reoccupation of vacant burrows can occur quickly. Predators like badgers, weasels, and raptorial birds provide sustained pressure and can reduce populations, particularly if multiple species are preying on RGS populations simultaneously. They are an important component of an integrated pest management strategy for RGS control. However, control is rarely fast enough to satisfactorily reduce damage when RGS populations increase rapidly.

To try to address questions about mid-season control with poison baits, we conducted a small, replicated trial in late June. Bait stations (Figure 2) were constructed and set approximately 150 feet apart on the edges of a mowed area of brome-alfalfa hay. Bait boxes were spiked with approximately 20 grams of ZP Rodent Oat Bait AG. RGS within 50 feet of the box were counted before treatments, and daily for 10 minutes for the next five days. By day three, a 50 per cent reduction in RGS local population was observed for all stations. Two holes per box work well. Anecdotal evidence indicates RGS are less likely to feel trapped if there is more than one hole. These rodents are very curious and began investigating and entering boxes minutes after they were set.

This small test indicates that the use of bait boxes mid-season can reduce RGS populations, but reductions are not as profound as hole-applied baits in the spring. Local populations did not continue to diminish on days four or five. Consider too, that this test was over a very limited area. If this method is to be used for a large area, several bait boxes are required.