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Spray affects a major spartina grass site at Ruawai wharf, where after more than 12 months, the site is now almost clear.
The programme is a joint operation between the Northland Regional Council and Department of Conservation.
Kaitaia-based Northland Regional Council Land Management Officer Doug Foster says some harbours subject to a spraying programme for the past three years are now showing dramatic improvement.
“The Whangarei and Kaipara Harbours are good examples. Spartina grass that once grew there densely to chest height is now down to the odd leaf sticking out of the mud.’’
Mr Foster says spartina was introduced to Northland many years ago as a rough stock feed, to absorb wave wash on stopbanks and to catch silt.
“It’s another introduced plant that has been too successful in Northland’s environment, causing unforseen problems after its introduction,’’ Mr Foster says.
“We’re expecting the eradication programme on each site to take between four and eight years, depending on the site.’’
However, some small infestations are still being discovered.
“The intention is to work with all parties to remove this serious threat to Northland’s harbours while minimising inconvenience to harbour users. We spray during summer to tie in with when oyster farm beds are closed.’’
Mr Foster says some of the Northland infestations of spartina have boasted the largest specimens of the plant that he had ever seen.
“Some patches were more than 1.8 metres tall,’’ he says.
Mr Foster says in Northland, spartina does not flower or seed, but spreads entirely through runners or through chunks breaking off and floating to other areas.
“It’s a bit like kikuyu. Runners spread through mud increasing the patch size by between two and five metres a year.”
Control is being prioritised for treatment where there is the potential for rapid expansion or dispersal.
Mr Foster says there is already evidence of treated areas returning to their original state, in some cases sandy and pebbly beaches.