The latest Weeds CRC research confirms what farmers have feared for sometime - that herbicide resistance can be 'caught' from a neighbouring farm - but the organisation warns Australia's farmers to work with their neighbours, not blame them.

Furthermore, says the CRC, the development of herbicide resistance on a farm is often the sign of a good farmer.

'Our latest research confirms herbicide resistance can be 'infectious',' said Dr Chris Preston of the Weeds CRC/University of Adelaide.

'While resistance often develops on the property, the genes for it can also come in over the boundary fence -  as pollen, airborne seeds, in hay or in seed for sowing -  and farmers' concerns about how it is transmitted are valid.'

The research found that whether you 'catch' herbicide resistance from neighbouring farms largely depends on how the weed reproduces.

Pollen from some weeds, such as annual ryegrass (Lolium rigidum), can drift for several kilometres on the wind while other weeds, like wild oats (Avena spp.), need humans to move them around the landscape.

Weeds with 'parachute seeds' pose a similar drift problem.

But before you go blaming your neighbours, said Dr Preston, a leading authority on herbicide resistance, farmers should remember that herbicide resistance genes are naturally present at very low levels in the weed population across the landscape.

Dr Preston also said that the presence of herbicide-resistant weeds is not necessarily the sign of a bad farmer.

'When it first became widespread, herbicide resistance was regarded as something of a 'social disease' in the bush,' explained Dr Preston.

'People thought you got it because you were a bad farmer - and if you found some, you kept quiet about it.'

'In fact the opposite is true.  It was the good farmers who were first to see it - as they were the first to use minimum till and herbicide technology well.'

Once resistant weeds emerge and build up in the weed population, however, the risk of them escaping the farm onto another property increases if the weeds remain unchecked.

'Different tillage methods and different herbicide timing are exposing a new spectrum of weeds, some of which were never a problem before - but now they have found a fresh niche', Dr Preston said.

Often this has nothing at all to do with herbicide resistance - but simply reflects selection pressure imposed by changes in farming practices.

An all-too-common response to herbicide resistance has been to 'blame the neighbours' - usually either the next door farm, the shire council that sprays the road verges, or the railways.

Instead, suggests Dr Preston, it may pay to join forces with the neighbours to tackle the problem on a larger scale.

Just as farmers co-operate with one another to prevent salinity, bushfires or the physical transport of weed seeds, they need to take collective action to limit the airborne transmission of herbicide resistance genes.

'The answer lies in zero tolerance for problem weeds.  It means patrolling, and patrolling again, for any signs of survivors which may have withstood treatment with herbicides - and then hitting them with something else to stop seed-set,' Dr Preston said.

And the Weeds CRC reminds all Australian growers that the only answer to preventing herbicide resistance is to adopt integrated weed management.

'Adopting a strategy that combines chemical and non-chemical tactics for weed control is important for the long term sustainability of Australia's cropping systems,' said Dr Preston.

With the release of the Weeds CRC's Integrated Weed Management manual earlier this year, Australian farmers now have the tools and advice for effectively managing herbicide-resistant weeds.