STRATEGIES TO CONTROL RODENT DAMAGE IN SUGAR BUSHES: AN UPDATE

Efficacy trials using zinc phosphide (ZP) steam-rolled oats (2% a.i., EPA Reg. No. 56228-5), and cholecalciferol mixed (CHOL) grain bait (.075% a.i., EPA Reg. No. 12455-57), were conducted during summer 1990 to compare their effectiveness in controlling rodent damage to plastic tubing systems used to collect sap from sugar maples (Acer saccharum) in Vermont. A 24(c) Special Local Needs registration for ZP to control rodent damage has existed in Vermont since the 1960s. However, no formal efficacy trials have been conducted for this specific use of ZP, and the previous supplemental label did not include instructions for prebaiting or bait reapplication. Cumulative catch estimates of squirrels (Sciuridae) before and after rodenticide applications indicated that both ZP- and CHOL- treated baits may be effective in reducing tubing damage in areas where damage is particularly severe. In an effort to gain more insight into red squirrel (Tamiasciurus hudsonicus) movements in and around sugar bushes (woodlots managed for maple syrup production), 10 red squirrels were fitted with radio collars and monitored twice daily from August through October 1990. Red squirrel movements were often centered around small stands of conifers (29%), isolated apple (Malus spp. ) trees (5%), and scattered blackberry (Rubus spp. ) and raspberry thickets (12%), even though these areas comprised only a small portion of the sugar bush studied. In addition, habitat evaluation suggests that sugar bushes where tubing damage is most severe often have higher total basal areas. Management of sugar bushes to reduce these habitat types may decrease tubing damage.