FIELD-TESTS OF DENATONIUM BENZOATE TO REDUCE SEEDLING DAMAGE BY POCKET GOPHERS (THOMOMYS TALPOIDES RICH.)

The repellency of a bitter compound, denatonium benzoate; to reduce po cket 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 ap plied to both roots and foliage; and no chemical application (i.e. con trol). No significant difference between treatments was noted for pond erosa pine (Pinus ponderosa Dougl.) or Douglas fir (Psendotsuga menzie sii (Mirbel) France) seedlings suffering gopher-related mortality. Non -animal mortality (58.2% of all seedlings) accounted for a greater los s of seedlings than gophers (38.2%). Composite foliage and composite s oil samples collected from the treatment plots were all negative for t he presence of denatonium benzoate. In the Idaho trial (1993 to 1993), 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 portio n (72.5%) of all seedlings was destroyed by gophers. It appears that t he bitter compound, denatonium benzoate, as evaluated in these trials, is not an effective gopher repellent. Published by Elsevier Science L td.