Product Name: Overwatch® Herbicide
Active Constituent: Bixlozone (isoxazolidinone), powered by Isoflex™ active
Formulation Type: Suspension Concentrate (SC)
Proposed Use Rate: 1.25 L/Ha
Technical Highlights:
Some agronomists theorize that Overwatch® Herbicide is highly volatile and suggest volatilization is causing bleaching in some off-target crops.
The APVMA has classifications for how volatile a chemical is. Extensive studies found that Overwatch® Herbicide is not considered to be a highly volatile chemical.
This finding was concluded by considering a number of different factors including vapor pressure, water solubility, soil binding coefficient and formulation type.
Review of studies by the APVMA, concluded that volatilization and atmospheric transport following application are not likely to be significant for Bixlozone*.
Overwatch® is not considered to be a relevant residue in air.
*Public release summary on evaluation of new AI Bixlozone in the product Overwatch® Herbicide. APVMA product number 86427. Dec. 2019.
Some agronomists have suggested that rain events a long time after application cause Overwatch® Herbicide to rise through soil, volatilize into vapor, and cause signs of bleaching in off-target crops.
This suggestion focusses on only one dimension of a multi-dimensional issue. The issue could involve impacts from spray drift, delayed symptom expression after drift, or low-level localized volatility, alone or in combination.
Any rainfall that occurs a long time after application will likely increase downward mobility of Overwatch® Herbicide (rather than promoting upward movement and subsequent volatility). Bixlozone is known to exhibit moderate mobility in soil.
FMC has considered possible explanations as to why we see such a long time between potential drift at the time of application, and expression of symptoms in off-target plants. Three possible explanations are delayed expression of drift symptoms, localized volatility at low levels, and plants not being in a suitable vegetative state to express drift symptoms when they occur.
As with the introduction of any new product we continue to monitor observations in the paddock and review those observations as they arise.
Some reports and social media posts show a field of lupins that the post or report says exhibit signs of bleaching.
Approximately 99% of the 1.2 million ha of paddocks to which Overwatch® Herbicide was applied this year has not reported off-target crop bleaching.
However, some off-target bleaching of lupins was observed in nearby paddocks. That observation showed that bleaching occurring from 300 meters to up to 1 kilometre away from the treated paddocks.
Ongoing monitoring by FMC is observing strong recovery from transient bleaching in the overwhelming majority of cases.
FMC has received numerous reports of Lupin crops immediately adjacent to Overwatch® Herbicide treated paddocks that did not experience any transient bleaching at all. Further investigation of these cases revealed that application of Overwatch® in the neighbouring paddocks was consistent with label instructions and good spray practices.
Some individuals have conducted their own tests by placing potted lupins into paddocks treated with Overwatch® Herbicide. Some of these potted lupins have demonstrated symptoms of bleaching.
FMC is aware that different people have been undertaking their own tests. We have not been involved with the methods they have been using. We are aware that some potted lupins have demonstrated transient bleaching, and some potted lupins have shown no transient bleaching.
We have been involved with scientific trials that were reviewed by the APVMA. Our results demonstrated that low-level volatility from treated soil is possible and is confined to a relatively short distance away from the application site.
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 validated data indicates the amount of volatilization causing such bleaching is very low, and too low to cause anything more than a transient symptom on sensitive vegetation such as lupins. By itself, this amount of volatilization cannot move very far, and decreases in concentration the further it moves from the source.
1.1 What actions are FMC taking?
FMC representatives are discussing the situation with the grower, obtaining all the relevant background information and inspecting the crop/s in question. At the same time all the relevant facts are documented, along with pictures, samples and other relevant items required to resolve the situation or provide an explanation. Should the FMC representative not be able to offer a solution or explanation, an FMC technical expert will visit the grower for a more detailed investigation.
1.2 Where are the specific geographical areas that reports are coming in from? Name the closest towns.
Most of the reports of off-target effects are from the central part of the WA wheat belt.
1.3 What do you do when you visit a farm based on receiving a report?
Once a report is received, an FMC representative will contact the farmer to discuss the observation, and if necessary, visit the farm to inspect the crop/s in person and follow up if required.
1.4 Who gets involved?
The local FMC representative, and/or technical expert and local agronomist.
1.5 If I have any questions or concerns, where can I get more information?
FMC Australasia works closely with industry to support the release of all its new products.
Our team remains committed to answering any questions our customers may have and provide technical support via our qualified agronomy team. If you are unsure who your local FMC team member is, please call FMC on 1800 901 939.
2.1 Some growers and agronomists are proposing to use lesser rates of Overwatch® Herbicide next season to reduce the amount of in-crop bleaching.
The use of any herbicide at reduced rates has the potential to compromise resistance management for the entire cropping system. The use rate on the label for of Overwatch® is 1.25L /ha and it is not recommended that a lesser rate be used. The registered rate was demonstrated to be the rate of optimal herbicidal efficacy and crop selectivity as confirmed by the APVMA efficacy and crop safety review during the registration process.
2.2 Should Overwatch® Herbicide have been used with disc seeders?
That was not recommended. The Overwatch® label specifically provides that:
“Overwatch® should be applied prior to sowing and incorporated by sowing using knife point and press wheel equipment”, and that “Crop safety from the use of disc seeders is variable”. Growers should follow the Overwatch® label.
2.3 Why are disc seeders not recommended for use with Overwatch® Herbicide?
Disc seeders vary in their ability to move herbicide treated soil out of the furrow, thereby minimizing the risk of germinating seeds coming into contact with the herbicide. When using a disc seeder the reduced soil disturbance means that there is greater potential for treated soil or the herbicide solution to come into contact with the germinating seed due to lack of positional selectivity. If there is heavy rainfall after sowing, the herbicide solution or herbicide treated soil may be washed into the seeding slot where it can come into contact with the germinating seed.
Disc seeders can also actively move herbicide treated soil into the furrow slot during the sowing operation. Another potential risk of disc seeders relates to the ability of the closing wheel to successfully close the furrow in wet conditions. If the seeding slot is not fully closed over, the potential for increased crop damage may be higher.
2.4 When applying Overwatch® Herbicide, what is the recommended set up of the spray rig?
It is recommended that Overwatch® be applied in at least 80 L/ha as a coarse quality spray.
The most preferred application regime for Overwatch® also includes:
2.5 What can growers do prior to, or during sowing that can help Overwatch® Herbicide do its job effectively?
As with all products, following the label directions and precautions will ensure optimum product performance.
3.1 Is Overwatch® Herbicide prone to drift?
Like every other herbicide, drift from Overwatch® can occur when Best Management Spray Practices* are not followed. It is droplets that drift, and whatever the droplets contain will be carried with them.
The three types of drift that may occur are droplet drift, vapour drift and particulate drift. Particulate drift can also include the movement of product carried by dust from strong winds or seeding machinery. These are aggravated by surface temperature inversion, and high relative humidity conditions that prolongs the survival of airborne droplets.
*GRDC. Sprayright – to avoid drift. Spray Best: Best Practice Guide for Ground Spray of Pesticides.
3.2 What are the key factors to minimising drift?
Good spray application management employs a number of techniques to minimise off-target movement.
3.3 We hear that the chemical is being drifted onto neighbouring crops – is this normal and should farmers be concerned?
No, this is not normal, because drift, regardless of which herbicide is being used, should not occur when good spray practices are followed.
FMC will continue to monitor the situation and work with industry partners and will provide an update once more information becomes available.
3.4 How many farmers have reported they have experienced issues with spray drift?
Of the approximately 1.2 Million ha’s treated in Australia, we are aware that less than 1% are showing signs of off-target bleaching. This involves 50-60 farmers.
3.5 When applying Overwatch® Herbicide, what special precautions are required to minimise the risk of spray drift?
For all pesticide applications, follow Best Management Spray Practices that employ a number of techniques to minimise drift (see point 2).
Best Management Spray Practices that are recommended for Overwatch® are detailed under the Spray Drift Restraints heading on the product label and include:
3.6 What are typical conditions under which surface temperature inversions are likely to appear?
Surface temperature inversions usually occurs on clear, calm mornings and nights. Windy or turbulent conditions may prevent inversion formation*
Inversions can transport pesticides for long distances, and not necessarily into adjacent paddocks only.
*NSW Department of Primary Industries. Reducing herbicide spray drift (nsw.gov.au)
3.7 What happens to non-target crops impacted by Overwatch® Herbicide spray drift?
Available data indicates that the bleaching effects on non- target crops are transient. Initial reports show that any bleaching effects are not lasting and that crops recover from bleaching.
3.8 There are reports of bleaching symptoms similar to that caused by Overwatch® Herbicide on roadsides and other natural vegetation. How can this be explained?
We are aware of some reported bleaching of weeds like Bifora and Sow thistle on the side of roads. Given its high level of sensitivity to Overwatch®, these weeds are often the first to exhibit bleaching symptoms. The incidence of such symptoms is indicative of off-target drift. Use of best practices for spray drift management will enable growers to prevent this from happening.
The effect on the weeds that has been reported does not mean that Overwatch® is the only chemical present. While the symptoms caused by Overwatch® on these weeds is most obvious, the effects of other herbicides can also be seen in many cases. If there are Fine particles in the spray mixture they will drift – including every other herbicide in the spray tank.
Growers concerned about off-target drift should seek agronomic advice and where appropriate report spray drift to the APVMA by submitting an on-line Adverse Exposure Report via the link:
3.9 How many cases of off-target bleaching are you aware of?
To our knowledge FMC has received a number of reports of off-target bleaching, mainly in WA. Of the approximately 500 000 ha’s treated in WA, we are aware that only about 1% are showing signs of off-target bleachin58g. The company is looking into each report received to better understand the situation.
3.10 Are there any crops that are more sensitive to drift from an Overwatch® Herbicide application?
After one season of full-scale commercial use, Lupins, Serradella, Tillage radish, Chicory and Biserulla appear to be more sensitive to Overwatch® spray drift.
3.11 Is the use of a drift-mitigating agent recommended for Overwatch® Herbicide application?
A drift mitigating adjuvant may be added to further minimize fine droplet production, and to enhance soil deposition in standing stubble.
A greater proportion of coarse droplets in the spray mixture will further reduce the potential for particulate drift and vapour drift to occur.
4.1 Does the mixing of Overwatch® with other chemicals change its volatility profile?
Certain Emulsifiable Concentrate (EC) formulations and spray adjuvants are known to increase the percentage of fine droplets during application. Fine droplets will not fall to ground under their own weight and will be taken wherever the wind carries them.
4.2 Some people have been saying that they are seeing only symptoms of Overwatch®, and not other mix partners, in drift situations. What is FMC’s response?
When Overwatch® is used in combination with other herbicides, all products in the tank have the potential to cause symptoms in different ways, some of which are more difficult to detect.
8.1 Is Overwatch® Herbicide (Bixlozone) considered to be a volatile herbicide? Some reports suggest that the product moves around…
Overwatch® Herbicide (Bixlozone) is not considered to be a volatile herbicide, because:
For an application rate of 300 g Bixlozone/ha the amount of volatilisation from the application was low (maximum 0.42% at 1m from the application site 72 hours after application) and was seen to decrease with increasing distance from the application site, with <0.05% of the application rate detected at 20 m from the application site.
The degree of bleaching of the sensitive indicator plant Stellaria media (Chickweed) associated with the volatilisation of Bixlozone was also seen to be low, with a maximum of 13% total leaf area bleached in plants located 1m from the application site. In plants located 20m from the application site no bleaching was observed. Any bleaching was seen to occur 7 days after application, but not before.
These observations correlate with the degree of volatilisation observed in the APVMA report.
Overwatch® is not considered to be a relevant residue in air.
* Public Release Summary on the evaluation of the new active bixlozone in the product Overwatch® Herbicide. APVMA product number 86427. December 2019
8.2 Was Overwatch® Herbicide fit for commercial launch in Australia?
Yes. Overwatch® was fit for commercial launch in Australia. The complete regulatory package was evaluated by the APVMA, which is a world class regulator committed to regulatory and scientific excellence.
A complete registration package takes over 10 years to generate, and costs approximately $280 million* to compile. This includes an extensive range of studies covering toxicology, metabolism, residues, environment, efficacy, and crop safety.
Bixlozone was first developed in the 1980’s, and studies have been undertaken since then. A substantial volume of information about this product exists.
*Phillips McDougall
The Cost of New Agrochemical Product Discovery, Development and Registration in 1995, 2000, 2005-8 and 2010-2014. R&D expenditure in 2014 and expectations for 2019
