Control of Black Oak and Tanoak in the Sierra Cascade Range

Abstract

Abstract Broadcast, directed, and stem injection herbicide techniques were applied to 3- to 8-year-old black oak (Quercus kelloggii) and 3-year-old tanoak (Lithocarpus densiflorus) clumps (directed applications only). Broadcast applications of imazapyr at all rates to black oak and directed applications of imazapyr to tanoak performed better with the addition of an adjuvant compared to treatments without the adjuvant. However, even with an adjuvant, broadcast treatments of imazapyr at or below 560 g acid equivalent (ae/ha) only suppressed black oak growth and did not provide long-term control. Directed applications of imazapyr gave excellent control of both black oak (0.43–2.17% ae plus Sylgard) and tanoak (0.14–1.13% ae plus Hasten) clumps. Imazapyr was more effective than basal bark treatments with triclopyr (8.9% ae), and tank-mixing imazapyr with glyphosate did not improve the level of control. Stem injection treatment of black oak trees or clumps with imazapyr was very effective with nearly all rates and hack intervals, but late summer or fall applications gave greater suppression of basal re-sprouts compared to spring and early summer treatments. These results demonstrate that imazapyr is a very effective and versatile tool for the control of black oak and tanoak clumps and black oak trees. West. J. Appl. For. 19(4):268–276.