Lagarosiphon major is a priority invasive species first recorded in a natural Irish watercourse, Lough Corrib, in April 2005. The weed has subsequently expanded its range significantly within the upper and middle lake but, as of 2010, has not been recorded in the large lower lake. In Lough Corrib the temporal growth pattern exhibited by L. major is at variance with that displayed in its country of origin. In southern Africa the plant grows most vigorously in summer, whereas in Corrib it achieves its best vegetative expression during the colder and darker winter months. This temporal growth pattern significantly influences practical weed control programmes, as it has proved to be far more efficient to cut and harvest L. major stands when the stems are erect and buoyant, even if it does mean that cutting operations must be conducted during the more inclement winter months. A combination of traditional and innovative weed control methods are used to control L. major in the lake. These include manual removal using scuba divers, mechanical cutting and harvesting, chemical control and light exclusion using a natural jute matting material. In 2008 L. major occupied c. 92ha of lake bed, while some 8,500ha is deemed to be suitable for its establishment and growth. Control work to date has reduced the area of lake occupied by this aggressive weed to c. 35.9ha
