AgResearch weed scientist Trevor James says he didn't know what he was looking at, at first.

It was a photograph of velvetleaf (Abutilon theophrasti), one of the worst weeds in America and possibly the world.  And it had just been found growing in the Waikato.

"When I realised, panic buttons went off.  Because I knew from the literature that this is a really terrible weed."

It is now known to be growing at two sites in the Waikato, near Te Kauwhata and Waihou.

A member of the mallow family, the plant has small, yellow flowers and large round leaves.  It grows upright in a similar manner to hollyhock.  "Growing with a maize crop, it will get up to three metres tall.  Its seed pod is the distinctive thing, it's cup-shaped and rough to the feel."

Dr James is working with Biosecurity NZ, the Foundation for Arable Research and Environment Waikato.   "We'll be looking at putting out an industry update on all the information we can get but right now we really want people to look out for it, and get in touch if they think they have seen it."

Velvetleaf had been reported in New Zealand in 1978, in Ararimu (Hunua district), and was believed to have come in with millet seed.

"Here it is known as butter-print. We thought it was a casual escape, and believed it had been dealt with.  We don't know if it's taken from 1978 to now to spread into agriculture, or if this is a second border incursion.  Sometimes, for reasons we don't understand, a weed that has been in the country for a while can suddenly become a problem."

velvetleafVelvetleaf may be difficult to control chemically, he says.  "The worry is that this weed will come up after the usual herbicides have been used, and done their thing.  Normally, in a maize crop, once you get a canopy, you don't expect weeds to be a problem.  But velvetleaf, it appears, will grow happily in those conditions and produce seed - before the maize is harvested.  And from there it can get spread around because of the way the dairy industry operates now."

In America, which produces 50 per cent of the world's maize, velvetleaf is said to be the worst weed.  Uncontrolled, it can reduce crop yields by up to 34 per cent, costing hundreds of millions of dollars per year.

Velvetleaf was introduced to North America in the 18th century from China and has now become their foremost broadleaf weed in maize and soya bean crops.

"The thinking is that the worst weed in America is going to be the worst weed nearly anywhere."

  • Contact Wendy Mead, Biosecurity NZ officer, if you think you've seen velvetleaf.  Phone 0800 800 401.