Wheel weedy

Intermediate School student Hugh Mckenzie gets elbow-deep in mud and finds that dirty vehicles could be spreading weeds into reserves.

Scraping arm loads of mud from dirty trucks may not be the first thing you think of for a school science fair project, but for 12 year old Hugh Mckenzie it was a winning formula. Hugh's project on whether dirty vehicles harbour weeds took top honours at the Central Northland Science Fair. With help from Northland Conservancy, Hugh conducted a simple but effective experiment to see whether weeds can be spread by off road vehicles.

Over summer and autumn Hugh, with a little help from DOC staff (including his Mum and Dad, who both work for DOC) collected mud samples from 20 DOC trucks around Northland. He planted out his muddy samples in a glasshouse and for five months watched what grew. 495 plants of 29 different species emerged from the samples, and alarmingly most of these were exotics and some were environmental weeds. This proves that dirty vehicles are able to carry weed seeds, and could be spreading weeds into reserves. Hugh found that invasive species such as kikuyu and veld grasses can be transported by dirty vehicles. Both of these can be serious problems, smothering low growing plants, cutting out sunlight and preventing regeneration of native species.

The message from Hugh's muddy experiment is clear as crystal: clean your vehicle!

Hugh recommends that all vehicles should be cleaned before going out into reserves; whether they are private recreational vehicles, or Department of Conservation work trucks. And clean means clean. Simply taking a vehicle through a service station car wash is not enough because the undersides of vehicles and around tyres and mud flaps do not get cleaned.

Washdown facilities are the best option, and Hugh suggests that all DOC offices with off-road vehicles should have access to washdown bays. Washdown bays need to comply with local council laws and are not cheap, costing around $14 000. But the old adage "Prevention is better than Cure" needs to be seriously considered, and it may well be a case of "Prevention being more cost effective than the Cure."

Hugh also recommends that care should be taken to keep to marked tracks and roads, and in high value reserves tracks may need to be rerouted or closed completely.

Many invasive weeds can establish from plant fragments that are also easily spread by vehicles, for example the aquatic weed lagarosiphon. Fragments of aquatic weeds can get caught up on boating equipment, trailers, fishing, ski and swimming gear and then hitch a free ride to the next lake. Many lakes have signs reminding people to clean off gear before leaving a lake, and around Southland and Central Otago there is a campaign to remind people to do this.

Preventing weed spread is crucial for protecting many of New Zealand's unique reserves. Seed and plant fragment dispersal by vehicles is a very real risk.

How to help prevent weed spread:

• Be aware that weed seeds and fragments can be spread by vehicles, animals, in clothing, gear and equipment.
• Wash your vehicle properly (not a car wash) before going off-road in a reserve.
• Stick to marked tracks and paths.
• Clean all boating equipment and trailers from aquatic weed as soon as you are out of the water.
• Always cover trailers when you are moving a load of plant material.
• Dispose of garden waste in approved landfills or green waste sites, never dump it down the bank or over the fence as it may take root and grow.
• Never empty ponds or aquariums into drains or waterways.
• Learn to watch for weeds in your area.

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