Seasonal effects on mortality rates andresprouting of stems treated with glyphosate inthe invasive tree of heaven (Ailanthus altissima(Mill.) Swingle)

Tree of heaven (Ailanthus altissima) is regarded as invasive within urban and naturalareas worldwide. Efficient methods to control it are significantly needed if we are tolimit its well-known environmental and economic impacts. Up to now the use ofherbicides has proven necessary since following mechanical damage, Ailanthusvigorously resprouts. However, the seasonal response of Ailanthus stems, treated withherbicides, has never been assessed. We compared the control efficacy recorded inautumn, winter and summer in an abandoned suburban citrus grove in Sicily, underMediterranean-climate conditions. Glyphosate was injected within drill holes made inknee-high cut trees. Tree mortality and the resprouting ability of treated stems weresignificantly affected by the application timing and by diameter class of stems.Mortality was significantly lower in winter treatments within the smaller diameterclass. Within the larger diameter class, only autumn treatments showed a notablyhigher mortality rate and a significantly lower growth of sprouts. Hence, autumninterventions are strongly recommended to effectively treat Ailanthus. Mortality wasnotably higher in the smaller diameter class. Our results confirm the importance ofearly intervention to control Ailanthus, also showing that the choice of the season iscrucial to obtaining satisfactory control of its resprouting ability.