In 1999, after much research, and in cooperation with Ontario Beetles, staff released 5000 Galerucella species beetles to combat the “Purple Invasion” that had become well established at Cranberry Marsh during the 1990s. The release was in response to a recommendation from the Cranberry Marsh Zone Management Strategy . After the draining of the marsh in early spring 2001, the seed bank was exposed and as feared, many more Purple loosestrife plants appeared. In 2002, while there was some evidence of beetle activity, the loosestrife was thriving in dense populations, particularly along the west side of the marsh.

In the summer of 2003, during monitoring activities for the Durham Region Coastal Wetland Monitoring Project, a large population of the beetles was discovered. That same year, Ministry of Natural Resources Stewardship Rangers worked for two days in the marsh removing loosestrife flower heads totaling more than 1000 lbs. and they observed large numbers of beetles in the Purple loosestrife-infested areas of the marsh.

In 2004, while some Purple loosestrife still existed in the marsh, the reproductive ability of the plants had been seriously compromised by the presence of the beetle. The young succulent leaves of the plant provide the diet of choice for the beetles. As a result, the plants expend their energy producing additional leaves and, therefore, never reach the flowering or seed stage.

(Above) These photos, taken from the south platform off Halls Road on July 23rd, 2004, show the absence of flowering Purple loosestrife. Not all the plants are completely dead; however, there is generally less than 30 cm of this year’s growth at the base of last year’s dead stalks.

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