A biosecurity officer says farmers should treat their farms like an island - making sure they know what's coming on and what's going off - so they can stop the spread of highly invasive weeds.
Darion Embling from Waikato Regional Council says farmers in the region need to make sure machinery and feed coming onto their farms is free of soil and seeds that could bring in pest plants.
He says alligator weed is coming down from the north, mainly in stock feed, and machinery from the south could bring horsetail with it.
Mr Embling says keeping machines clean is a key way to stop weeds from invading the farm as about 80% of known weed species can be spread by machinery.
Farmers who want to know more can access the Machinery Hygiene Guidelines released recently by the Ministry for Primary Industries togther with other pest control agencies.