09 July 2009

Purple Loosestrife Biocontrol Update

About a month ago, I blogged about using Galerucella spp. beetles to control Purple Loosestrife (Lythrum salicaria). At that time, Galerucella beetles had just recently emerged, and we saw eggs, larvae, and a few adult beetles, but not much damage to the newly emerged leaves. I visited the same site a few days ago, and the damage to Purple Loosestrife was a much different story.

In the photograph above, you can see what looks somewhat like an herbicided plant. That's Purple Loosestrife after the beetles have done their job. This plant surely won't be producing any seed this year.

The photograph above is a close-up of the damage to Purple Loosestrife leaves.

In the photos above and below, you can see numerous Galerucella beetles covering Purple Loosestrife plants. I counted nine beetles in the photograph below!

There were several comments to my previous post on this topic. We don't know for sure what will happen long-term as a result of the introduction of these beetles. They may feed on our native Winged Loosestrife (Lythrum alatum) and cause similar results to that species. I had suggested that Hybrid Cattail (Typha x glauca) often becomes dominant in areas where Galerucella have been released; I have to correct myself. At these sites, Hybrid Cattail is in fact becoming the dominant in some areas, but native species including Blue Joint Grass (Calamagrostis canadensis), Water Sedge (Carex aquatilis), Jewelweed (Impatiens capensis), and Dotted Smartweed (Polygonum punctatum) are becoming dominant in other areas.

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