Watch out velvetleaf, Rusty the detector dog is on his way.

The weed is a nightmare for farmers, as it competes with crops for nutrients and water.

Rusty and his owner sniffed out 55 contaminated properties in last year's programme to destroy the weed.

Environment Southland's senior biosecurity officer Randall Milne said farmers need to check their crops.

"There's an ongoing need over the next couple of months for farmers to keep an eye out for velvetleaf, and report any plants that they do find through to Environment Southland or the Ministry for Primary Industries."

Randall Milne described velvetleaf as one of the world's worst crop weeds.

"It really reduces your crop yield, very difficult to control and the seed has a very long life in the soil as well."

Milne said the seed can live up to 60 years.