Overwatch moves outside boundary: trial
3 Aug 2021
AGRONOMISTS in South Australia have joined those in Western Australia who are dealing with frustrations from alleged off-target damage from new mode-of-action herbicide Overwatch, from FMC.
Earlier this month, Farm Weekly reported on claims from WA agronomists Wayne Smith and Frank Boetels that stated in most cases, there was no off-target damage from the product when it was dry, but after it rained, they started seeing off-target damage in all directions.
Those claims have now been backed up by independent agronomist Craig Davis, based in South Australia’s Mid North and Yorke Peninsula, who said he had seen movement outside paddock boundaries that didn’t match up with the direction of spray.
“We’ve got the predominant prevailing wind direction taking the original spray drift one way, but now we’ve got multiple cases where it’s moved in other directions outside of paddocks and accumulated on roadsides,” Mr Davis said.
“We have weather records and spray application data to rule out drift or inversion and while you can notice the majority of the product went where you would expect, it’s gone far further and caused much larger areas of off-target movement than we ever anticipated.
“Both WA and South Australia have very professional operators with very good set-ups and weather monitoring – they are aware of the risk of off-target damage and have quickly become embarrassed by the fact that Overwatch is moving outside their paddock boundaries.”
With that in mind, Mr Davis went about conducting a canary pot trial to try to ascertain if Overwatch was volatile and had been moving in ways it shouldn’t.
He took lupins from an undamaged paddock, dug holes to clear out any chemical that might be in the ground and embedded pots to within an inch of the soil surface in a paddock both one day and three weeks after spraying with Overwatch.
“That meant any gas, if it was a gas, could potentially come into contact with those lupins and if there were symptoms that would give a strong indication that we have a product moving after application,” Mr Davis said.
“I monitored those plants and found that after one week there was no damage, but after two weeks both paddocks showed damage, meaning we picked up damage well after the application of the spray.
“It was certainly activated following rainfall, but it wasn’t a lot of rain – the soil was already quite wet, but it didn’t become waterlogged and in that trial it was only off a 10 millimetre rainfall event.”
FMC head of development Geoff Robertson said the company understood that different people had been undertaking their own research.
“We have not been involved with the methods they have been using, but we are aware that some potted lupins have demonstrated transient bleaching and some potted lupins have shown no transient bleaching,” Mr Robertson said.
“FMC has been involved with scientific trials that were reviewed by the APVMA (Australian Pesticides And Veterinary Medicines Authority) – our results demonstrated that low-level volatility from treated soil is possible and it is therefore plausible that a sensitive plant such as lupins placed within an Overwatch treated paddock may show symptoms of transient bleaching.
“However, the available data indicates the amount of volatilisation causing such bleaching is very low and would be confined to a relatively short distance away from the application site.”
In June, Farm Weekly reported that a farmer from Bolgart had a lupin paddock which had suffered from alleged off-target drift and the bleaching effect had been undeniable.
FMC had always maintained that crops would recover from the bleaching and that has been exactly what the farmer from Bolgart has seen happen.
“The lupins are now all starting to flower and you can’t see any real difference to the ones that weren’t affected,” the farmer said.
“We checked all our records on spray dates for this paddock and we are thinking that the damage was caused by movement of droplets from the top of the hill down to the lower part of the paddock.
“That was likely due to spraying the paddock next door late in the afternoon with very low wind speed, warm temperatures and possible spray inversion.”
Mr Robertson said FMC appreciated the before and after comparison by the grower of the transient bleaching of the lupin crop and had been in contact with him.
“The recovery from spray drift is consistent with what has been seen in the recovery of many other cases where spray drift has occurred,” he said.
“Of the approximately 1.2 million hectares to which Overwatch was applied this year in Australia, we are aware of less than one per cent that are showing signs of off-target crop bleaching.
“As is the case with this grower, ongoing monitoring by FMC is observing strong recovery from transient bleaching in the overwhelming majority of cases.”
However it’s not just the off-target damage that is causing concern, with excessive levels of bleaching on crops that were sprayed with Overwatch as per the label instructions.
Mr Davis said he had recorded more than 60 paddocks, predominantly barley, with heightened levels of crop damage, above what was seen in trials.
While those crops, along with crops hit by off-target damage, are recovering, he said there were areas within them that were still severely affected with reduced growth, leaf area and tillering.
In some cases, paddocks in lighter soils had to be sown again.
“I’m hypothesising that lighter and loamier soils that contain more lime or bicarbonates are more prone to this occurring, whereas in other jurisdictions and States where their soil types are heavier with more organic matter, that is it not happening as readily,” Mr Davis said.
“If we do find that Overwatch is volatile, my concern is that the volatility is also part of the contributor to barley being so sensitive.
“If it is volatility that is causing off-target movement – and I do maintain we still need to prove how that is happening – and barley is sensitive to it being applied to the leaf, then that volatility could be a major factor for why we’re seeing such large scale damage to barley crops.”
Mr Roberts said some key cropping regions of WA had experienced an exceptional, historically wet season characterised by waterlogging and prolonged wet, overcast conditions, while in South Australia the majority of crops went in dry followed by large rain events and strong winds in some areas.
“Under these circumstances not only Overwatch, but also other commonly used pre-emergent products, exhibited more crop effects than what had been encountered in the preceding seasons,” he said.
“We could not have anticipated that based on the meteorological data and forecasts that were available to us.
“FMC will take the data that this experience has given us into account in our future research and development program.”
Like most growers around the country, Mr Davis wants to keep using Overwatch and knows how important it is for rotational purposes, however he does want answers as to why the product is allegedly moving so drastically off-target.
“I do accept that this product has very good merits – it’s a great active ingredient, it controls target weeds quite well and it is relatively safe on a number of crops including wheat and canola,” Mr Davis said.
“There are farmers and advisers out there, like myself who love this product and want to keep it as we need it for resistance management, but that cannot happen at all cost.
“As long as we can work out how to use it safely and minimise its potential for crop damage and off-target movement, I’d be happy to maintain using it.”