Crassula Erradication on the Dranges

On the 19th June the covers came off the ponds at The Dranges NR; time to see if the UV proof membrane had had any effect and with the licence from NRW in place and a good dry spell forecast it was time to drop the water levels in the pond and spray the invasive weed with herbicide for the first time.

The first thing we did was pump the pond to drop the water level. The herbicide will not work on submerged vegetation so we wanted to expose as much of it as possible without affecting the ecology of the pond.

We did the pumping first because crassula will happily colonise damp meadow habitats as well and there was a risk of breaking the weed into small fragments when removing the covers. Because we dropped the water levels by around 300mm a lot of crassula was exposed – this has meant that we could not really assess the effectiveness of the membrane and whether growth had been suppressed.

We are well into growing season and my feeling is that where the membrane was in contact with the water surface the submerged vegetation growth had been retarded. This makes sense, from research I have learnt crassula will photosynthesise day and night and will only make use of the UV spectrum below the water. When we replace the covers we intend to sink them to ensure all the weed is below water level.

The exposed crassula was left to dry and was then treated with herbicide. Let battle commence!