Discussion

Ailanthus trees appear to be easy to control with the herbicides used in this study. Burch and Zedaker (2003) also observed high control rates of ailanthus using basal application, with defoliation rates of 75-100% after six weeks using a variety of herbicide-carrier systems, most of which included Garlon 4. They observed 100% defoliation using Garlon 4 in a 20% formulation with HY-Grade EC used a carrier. The timing of application for that study was in June. The lower efficacy of both June and October basal bark applications in our study may be attributed to the use of kerosene as a carrier. While kerosene is relatively inexpensive and widely available, it is not specially formulated for herbicide applications as those used in Burch and Zedaker (2003).

The somewhat lower efficacy of the fall basal application treatment in our study in the fall may be due to the date of application (early October). This date is relatively late with respect to fall foliage senescence. Optimally, fall application should occur in late August through mid-September before the onset of leaf senescence which may limit translocated of the herbicide throughout the tree. The timing of spring application is probably also important, with the best likely timing occurring just after full leaf expansion, when trees have fully exhausted carbohydrate reserves, but have not passed the point of attaining a positive photosynthetic carbon balance.

Table 1. Mean (+ 1 standard error) percentage of trees in response classes of groups (n = 5) of ailanthus trees treated with cut stump application with Garlon 3A (degree of resprouting) or basal bark application with Garlon 4E (extent of crown mortality) either during the spring (early June, 2004) or fall (early October, 2003) as evaluated in June, 2005 (12 -19 months after application).

Table 1. Mean (+ 1 standard error) percentage of trees in response classes of groups (n = 5) of ailanthus trees treated with cut stump application with Garlon 3A (degree of resprouting) or basal bark application with Garlon 4E (extent of crown mortality) either during the spring (early June, 2004) or fall (early October, 2003) as evaluated in June, 2005 (12 -19 months after application).

Treatment

Crown dead - no resprouting

> 50% crown mortality - few weak sprouts

< 50% crown mortality - some resprouting

No visible crown effect - vigorous resprouting

Cut stump -spring

100

0

0

0

Basal bark -spring

95.8 + 5.3

4.2 + 5.3

0

0

Cut stump - fall

100

0

0

0

Basal bark - fall

91 + 5.6

9 + 5.6

0

0

Regardless of application type of season, the use of herbicides is important for controlling ailanthus. Manual cutting of ailanthus provides only temporary control and may ultimately lead to larger infestations of this species because of its ability to vigorously resprout from cut stumps (Burch and Zedaker, 2003). The rapid growth rates of ailanthus, particularly from resprouts (Miller, 1990) may allow for rapid recovery after cutting. Even with the use of herbicides, long-term follow-up control of treated areas is probably necessary. Ailanthus has prolific seed production (Miller, 1990) and the soil seed bank will likely produce seedlings at the base of treated trees for many years and will require repeated herbicide spraying.

Controlling the spread of ailanthus will likely be a long-term endeavor in many parts of the eastern United States. Ailanthus trees appear to be easy to kill, but the species difficult to control. Established stands of the species along forest edges, roadways, and disturbed areas provide seed sources for colonization whenever disturbances produce exposed soil and high light availability favorable for establishment of ailanthus. Ailanthus colonization of the interiors of logged stands in Virginia has been observed (Carter and Fredericksen, 2007) and herbicide treatment of ailanthus at the edge of these stands at the time of cutting may help reduce the extent of invasion by this species. Post-logging control of ailanthus seedlings and saplings may also be necessary. Knapp and Canham (2000) also found that ailanthus can invade natural gaps in old growth forests in New York. If established in closed forests, Ailanthus may also be able to persist through clonal propagation (Kowarik, 1995). Control of the spread of this species should focus on the removal of seed trees and vigilant control of regeneration both along forest edges and within forests where colonization has occurred.

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