Detailed information sheet

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Botanical name : Hydrilla verticillata Family : Hydrocharitaceae (frogbit) family  Common name : hydrilla  Also known as : Florida elodea, water thyme   Where is it originally from? : Europe, Africa, India, Sout East Asia, Australia What does it look like? : Submerged, bottom-rooting perennial growing to 9 m, with slender, brittle and branched stems (1 mm diameter).  Translucent, dark green leaves (6-12 x 2 mm) in whorls of 3-8 have distinctly toothed margins, and the plant also produces small tubers and turions (hibernating buds). Only male flowers are present in New Zealand, so no seed is set.  Are there any similar species? : Lagarosiphon, Egeria, Elodea are all similar.  Why is it weedy? : Grows in moderate to highly-lit submerged sites with low to high temperatures. Moderate growth rate, height, long life and density, and overtops smaller native species. Brittle stems break, and fragments and turions root downstream or wherever they are dumped. Lacks native plant competitors of similar height.  How does it spread? : Loose stem fragments root at any node and turions also form new plants. Spread within catchments by flowing water, and new catchments are infested by fragments spread by boats and trailers, (occasionally motor cooling water), eel nets, livestock, and diggers. Birds are unlikely to spread it.  What damage does it do? : Forms vast deep underwater ‘meadows’, shading out smaller native species and preventing seedlings of native species from establishing. Large clumps dislodge from the ‘meadows’, causing flooding. Rotting vegetation stagnates the water, killing fauna and flora. Which habitats is it likely to invade? : Rivers, lakes, dunelakes, and other waterbodies with moderate to high light levels.  What can I do to get rid of it? : Hydrilla is very rare in New Zealand, and control of any sites found should be undertaken by a specialised agency – contact you local Department of Conservation office or regional council for advice.  What can I do to stop it coming back? :

For more detailed botanical descriptions of weed species, check out the Plant Conservation Network's website at http://www.nzpcn.org.nz/exotic_plant_life_and_weeds/index.asp

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*The chemical control methods in this manual were devised by Department of Conservation staff for Department of Conservation operations and should not be used as a substitute for the pesticide manufacturer's label instructions. The Department of Conservation takes no responsibility for any liability or damage to any person, property or thing which may occur as a result of the use of any pesticide in accordance with the chemical control methods contained on this website.

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