Treatments  

Treatments in 1995 and 1996 focused on foliar applications of Bacillus thuringiensis variety San Diego (Bt) mixed with horticultural oil [F]. In 1997, Bt was used as the treatment in only one site.

Bt sprayed twice in each of two generations reduced damage to acceptable levels in treated plots by comparison to untreated plots (Fig. 6). Although these field applications have been successful, spray applications are not seen as a politically acceptable option by Neighborhood Services.

In 1997 our program concentrated on trunk injections of Imicide (imidacloprid) as the principal treatment where needed [G]. At the city cemetery, trees injected after monitoring at the first generation egg peak suffered only 5% defoliation compared to 25% in the control trees (Fig. 6).

In 1998 and 1999 our program concentrated on trunk injections of Vivid (abamectin) as the principal treatment where needed. At the city cemetery, trees injected after monitoring at the first generation egg peak suffered only 3% defoliation compared to 20% in the control trees (Fig. 7).

Each of these treatments are compatible with the monitoring program, as treatments made after egg peak sampling are effective at controlling any subsequent damage (Dahlsten et al., 1998).


[F] Foliar spray of Bt mixed with oil using a rotomist sprayer.


Fig. 6 Damage ratings for English Elms treated with Bt and Imicide vs control, Sacramento City Cemetery, 1997.


Fig. 7 Damage ratings for English Elms treated with Vivid vs. control, Sacramento City Cemetery, 1999.