Farmers and growers are being warned to look out for signs of weed resistance to the widely-used herbicide, glyphosate.
This follows confirmation of glyphosate resistance in both annual and perennial ryegrass in some Marlborough vineyards, where the chemical is regularly used to control weeds.
Foundation for Arable Research scientist Mike Parker is heading a Sustainable Farming Fund investigation and says the levels of resistance found are also much higher than expected.
He says other sites in the North and parts of the South Island are being checked, but so far there's been no evidence of glyphosate resistance on farms.
Mr Parker says the glyphosate resistance in ryegrass is a worry for farmers who often use the herbicide to kill pasture before resowing in grass or crops.
He's advising growers and farmers to alternate their chemical use to reduce the risk of increasing resistance.
Using hot air to control weeds
Meanwhile, the Future Farming Centre in Lincoln is investigating a non-chemical method of weed control, using heat.
The centre has adapted a thermal weeding system developed by Danish scientists which uses steam to kill weed seeds in the soil.
Centre head Dr Charles Merfield says using hot air to treat the soil before planting would be a lot less costly, in terms of fuel use.
"If you eliminate what's called the weed seed bank in the crop row no weeds will come up in that row at all, so it's potentially a very powerful technique."
Dr Merfield says so far, the Future Farming Centre has proved the hot air weeding concept in the laboratory and is looking for funding to take it out into the field.