Control of Ailanthus altissima in a historical fortress

The Citadel of Alessandria is a military fortress built in the 18th century, located in the north-west of Italy. It spans over 70 hectares and is composed of buildings, bastions, roads, all enclosed by a moat. Since 2007, the fortress was abandoned and gradually became invaded by weeds. One of the most problematic weed is Ailanthus altissima, a tree that colonized many areas in the fortress, including buildings and roofs, accelerating their deterioration. In July 2015, different Ailanthus control techniques were compared. In particular, cut stump and basal bark applications were tested in three areas of the fortress. The used herbicides were: glyphosate 360 g/l, fluroxypyr 20 g/l+triclopyr 60 g/l and aminopyralid 35.5 g/l+ fluroxypyr 144.1 g/l, each diluted 1:10 with water. For cut stump application the plants were first cut at the base and immediately sprayed on the cut surface. Herbicides were applied using a 2 l pressure spray bottle. Untreated cut plants were used as a comparison. For basal bark application, the lower 50 cm of the plants were sprayed with the herbicides by using a backpack sprayer. After 50 days from the treatment, an efficacy assessment was performed by counting the resprouts and their height in the cut stump application, and by observing the symptoms in the basal bark treatment. In the case of cut stump treatments, the number of resprouts ranked as follows: untreated > glyphosate > fluroxypyr+triclopyr > aminopyralid+fluroxypyr, with 4.7, 2.0, 1.3, and 0.06 resprouts per plant, respectively. The same ranking was observed for the height of the resprouts, with 20 cm observed for aminopyralid+fluroxypyr and up to 75 cm for untreated plants. For basal bark application, very limited symptoms were observed on the treated plants.