Plant Doctor Archive

Pesky bullrushes

Question I HAVE a large dam/pond which is rapidly being taken over by bullrushes (raupō?). The pond has tadpoles, ducks and freshwater crayfish in it, so we are very cautious about spraying, but after trying to pull them out and/or hack them down we are unsure of what to do next. They are as rampant as bamboo. Apart from getting a digger in to dig the pond up, can you suggest any way we could tackle this problem? Soon the ducks will have nowhere to swim and I would prefer lilies and irises in and around the pond.

Answer IT sounds as if the dam may be shallow, as raupō is a marginal plant and usually does not venture out into deep water. As you mentioned, I would hesitate to use chemicals where there is a lot of marine life and ducks. Activated Amitrole is effective on raupō, but you would need to gather extra information about how safe it is to use around water. I have only ever used it in the garden.

Short of pulling out by hand, which is difficult, or digging the pond out and replanting with marginal plants such as astilbe, gunnera, hosta, iris, lobelia cardinalis, mimulus and primula, I cannot offer too many other suggestions. The digger sounds like a good option to make the dam deeper.

Your local council’s noxious weeds inspector should be able to offer some advice.