58 DiTomaso and Kyser: Control of Ailanthus altissima treatment, because glyphosate is not lipophilic and cannot be mixed in oil. An oil carrier is necessary to penetrate the tree bark. Either Chopper or Garlon 4 (20% in Hasten oil) was applied to cover the basal 45 cm (18 in) of the tree trunk using a bottle sprayer. Trunks were sprayed to wet but not to runoff. An average of 60 mL of total solution was applied to each tree. Evaluations and Analysis At the University of California, Davis, site, each tree (repli- cate) was visually estimated for percent crown reduction 8 (June 1999) and 21 months (July 2000) after treatment. Evaluation of percent crown reduction in all trees were based on a relative comparison of foliage canopy in an undamaged tree. In addition, measurements were made of the percentage of trees with resprouts as well as the number and height of resprouting stems. In the Putah Creek site, visual estimates of percent canopy reduction and canopy vigor were determined in August 2002 (10 months after treatment) and August 2003 (22 months after treatment) for each tree. Vigor measurements were vi- sual estimates based on comparison with undamaged foliage of untreated trees and ranged from 0 (dead) to 10 (undam- aged). In addition, the percentage of trees that resprouted was recorded and resprout vigor, number, and height were visu- ally evaluated or measured. For standing-tree treatments, canopy reduction and vigor were compared across all treatments (including uncut con- . trols) using analysis of variance (ANOVA), and means were separated using the Student-Newman-Keuls (SNK) test ( 0.05). For stump treatments, the presence or absence of stump sprouts was compared across herbicide types, within each parent treatment technique, using logistic regression ( 0.05). Vigor of stump sprouts (including stumps with no sprouts, which were assigned a vigor rating of 0) was com- pared using ANOVA and SNK. Cut-stump subtreatments (time interval between cutting and herbicide application) were compared within each herbicide and within each parent application technique using logistic regression and ANOVA. Time subtreatments were grouped by herbicide within each parent application technique after it was determined that time interval had no effect. RESULTS AND DISCUSSION At the University of California, Davis site, manual cutting used alone provided little, if any, control of tree-of-heaven. By 10 months after cutting, small and large stumps produced between three and nine new basal sprouts (Table 2). By 21 months after cutting, ≈25% to 30% of the cut trees died, but the remainder averaged ≈4 new sprouts per stump. These new sprouts were an average of 1.6 to 2 m (5.3 to 6.6 ft) in height. Burch and Zedaker (2003) also showed that mechanical cut- ting stimulated tree-of heaven resprouting (1.6 new sprouts per stump) and increased overall stand density. They simi- larly showed that 21% of the cut stump trees failed to re- sprout. Table 2. Tree-of-heaven control using stem injection treatment with undiluted imazapyr as an emulsifiable concentrate (Stalker) or water-soluble (Arsenal) formulationz Evaluation 8 MAT* Treatment Cutting date Mean number of sprouts Imazapyr (Stalker) Small trees (4–8 cm diameter) 4 MAT 0 8, 12 MAT — Medium trees (8–16 cm diameter) 4 MAT 0 8, 12 MAT — Mean crown reduction (%) — 97.9 ± 5.2 — 96.9 ± 4.4 Clumps, 1/2 dose —— 84.2 ± 14.6 —— — Clumps, 1/4 dose —— 76.0 ± 8.9 —— — Untreated small trees 4 MAT 2.75 ± 3.10 — 8, 12 MAT — 0 70.8 Untreated medium trees Imazapyr (Habitat) Medium trees (8–16 cm diameter) 4 MAT 0 8, 12 MAT — Untreated medium trees 4 MAT 2.75 ± 2.50 — 8, 12 MAT — — 4 MAT 9.25 ± 4.27 — 8, 12 MAT — ©2007 International Society of Arboriculture 94.8 ± 5.8 26.3 ± 37.4 3.8 0 1.6 8.3 75.0 — 1.0 4.0 *Months after treatment (4 MAT February 1999; 8 MAT June 1999; 12 MAT October 1999, 21 MAT July 2000). 0.6 2.0 — — 99.3 ± 0.6 81.7 ± 18.9 12.5 1.0 0.4 — Percent of stumps with sprouts Evaluation 21 MAT Mean number of sprouts on sprouting stumps Mean height of sprouts (m) Crown reduction (%)
January 2007
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