Plant cuttings of invasive alien Impatiens glandulifera Royle develop flowers and produce viable seeds

Controlling the invasive alien Himalayan balsam Impatiens glandulifera is both expensive and time-consuming. The most promising control methods include manual mowing and hand-pulling. However, long-term effectiveness of these methods can be unsatisfactory. We hypothesized that such partial success might result from eradication efforts occurring too late in the season, allowing improperly treated cuttings to flower. Moreover, we experimentally tested whether cut flowering individuals left on the ground could survive long enough to produce viable seeds. The experiment involved plant cuttings and reference individuals. We recorded the number of flowers on each plant, monitored floral visitor activity, and simultaneously measured abiotic factors (air temperature, solar radiation, wind speed). The relationship between insect visitation rates and both flower abundance and solar radiation was nonlinear, highlighting the importance of considering complex environmental effects in pollination dynamics. The seeds were collected, and seed viability was compared between the two treatment groups. We demonstrated that the plant cuttings survived for about three weeks, developed flowers and produced viable seeds. Although the reference individuals had more flowers and were more frequently visited by insects (mainly Bombus pascuorum), they did not develop significantly more viable seeds than the cuttings. This confirms the remarkable survival capacity of I. glandulifera plant cuttings and supports our hypothesis that this feature may hinder the full eradication of the species through mowing and hand-pulling under current guidelines. Based on our results, we recommend changing the control timing.