Field tests of denatonium benzoate to reduce seedling damage by pocket gophers ( Thomomys talpoides Rich.)

Abstract

The repellency of a bitter compound, denatonium benzoate, to reduce pocket gopher damage to conifer seedlings was tested in two independent field trials in Oregon and Idaho. In the Oregon trial (1992 to 1993), treatments included a denatonium benzoate tablet placed in-ground with the seedling roots; a tablet plus denatonium benzoate foliar spray applied to both roots and foliage; and no chemical application (i.e. control). No significant difference between treatments was noted for ponderosa pine ( Pinus ponderosa Dougl.) or Douglas fir ( Pseudotsuga menziesii (Mirbel) Franco) seedlings suffering gopher-related mortality. Non-animal mortality (58.2% of all seedlings) accounted for a greater loss of seedlings than gophers (38.2%). Composite foliage and composite soil samples collected from the treatment plots were all negative for the presence of denatonium benzoate. In the Idaho trial (1993 to 1994), similar treatments (but with an additional spray-only treatment) were used on ponderosa pine seedlings. There was no significant difference in gopher-related mortality levels between treatments. A large portion (72.5%) of all seedlings was destroyed by gophers. It appears that the bitter compound, denatonium benzoate, as evaluated in these trials, is not an effective gopher repellent.