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Salv inia – a weed of nat ional s igni f icance

Selecting a release site Selecting the right site maximises the initial survival and establishment rate of the salvinia weevils.

How to get the best out of salvinia weevil releases

Select release sites with:

■actively growing salvinia (new bright green tip growth)

■open areas that receive direct sunlight for a major part of the day

■ free-floating salvinia in at least 10 cm depth of water

■a static weed mat.

Don’t select sites with:

■old, brown or multilayered salvinia

■shaded areas where there is an over-storey of other vegetation

■shallow water that may dry up seasonally

■sparse or primary form salvinia.

Releasing the weevilsAt the selected site release at least 300 adult weevils together in one area. As a guide this normally equates to 2 × 40L tubs.

Releasing them together helps keeps the population as close as possible, which increases breeding rates and leads to faster control. At large sites weevils can be released into a 1m × 1m quadrant, which helps contain them whilst populations are growing.

Don’t scatter small populations of weevils (less than 300) across an infestation as this increases the likelihood of the population dying out.

How to get the best out of salvinia weevils.

How to get the best out of salvinia weevils.

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When releasing the weevils:

pick a spot about 3 or 4 metres from the water’s edge if possible1.

make a small space (1 m diameter) in the weed mat where the host salvinia can 2. be placed in direct contact with the infestation

ensure the host salvinia is in contact with the water surface 3.

complete and return the weevil release form to your supplier.4.

If using extracted adult weevils they can be tipped from the small containers directly onto the infestation.

Ensure that salvinia has been positively identified before you introduce host salvinia containing weevils.

How long can it take for weevils to work? Populations of weevils can take 12–36 months to form a sufficient population and cause the floating salvinia mats to collapse. During this time the salvinia can appear healthy with very little visual evidence of the weevils’ impact.

The following photos provide an example of how the biological control works from when a sufficient population is reached to when control is achieved.

Monitor the weevil population monthly to determine if it’s increasing. Detailed information and instructions for monitoring weevils are contained in the salvinia control manual (www.dpi.nsw.gov.au/agriculture/pests-weeds/weeds/profiles/salvinia)

Photo: CSIRO Entomology

Photos: Tweed Shire Council

12–36 months after release – salvinia appears healthy

1 month later – salvinia turns brown due to weevil damage

2 months later – weevils begin to collapse mat

3 months later – control achieved

Salv inia – a weed of nat ional s igni f icance