Overwatch™ Herbicide

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:

  • Long-lasting residual control of Annual ryegrass including herbicide resistant biotypes and regionally specific broadleaf weeds
  • New herbicide molecule - Group Q mode of action
  • Pre-emergent herbicide for application as an IBS (Incorporated By Sowing) treatment for use in Wheat, Barley and Canola

When will Overwatch® Herbicide be available?

Registration was approved by the APVMA in April 2020, and Overwatch® Herbicide will be available for the 2021 season.

How does Overwatch® Herbicide work?

As a group Q product, Overwatch®Herbicide inhibits susceptible plants from producing carotenoids. Carotenoids protect chlorophyll in plant cells and help in the photosynthetic process of the plant. While susceptible weeds are unable to metabolise Bixlozone and eventually die, tolerant crops will metabolise the product and continue growing.

This process relies upon the metabolic ability of the plants and therefore if a crop is not actively growing, crop discoloration may persist e.g. under cold, frosty conditions.

What is the crop safety of Overwatch® Herbicide?

Several years of Overwatch® Herbicide trial data in Australia has shown a high level of crop safety with little to no effect on vigour despite early discolouration of the crop.

There are many factors that affect the crop safety of all pre-emergent chemistry. These include the separation of seed from treated soil, correct sowing methods and using correct rates. The Overwatch® Herbicide label contains clear guidelines in this regard.  

Do you foresee any compatibility issues with Overwatch® Herbicide?

We are currently undertaking extensive compatibility work, and from the information gathered so far, we have not seen any issues with commonly used knockdown herbicides or relevant insecticides.

What is the incorporation time for Overwatch® Herbicide?

The Overwatch® Herbicide label recommends incorporation within three days of application.

Overwatch® Herbicide has low volatility.

What is the length of control expected from Overwatch®Herbicide?

While there are several different factors that affect the length of residual control, the chemical characteristics of Overwatch® Herbicide and trial data indicate equal or better control than other pre-emergent products on the market. Several field studies have demonstrated control up to 70 days after application.

These characteristics include relatively long half-life, low volatility and a moderate carbon binding capacity when compared to other pre-emergent herbicides.

What are the potential re-cropping issues of the product?

Due to the wide range of crops being investigated for Overwatch® Herbicide we do not perceive there to be any major re-cropping issues. This information will be stipulated on the label.

On the label, what weeds will Overwatch®Herbicide control?

  • Annual ryegrass (Lolium rigidum)
  • Silvergrass (Vulpia bromoides)
  • Bifora (Bifora testiculata)
  • Sowthistle (Sonchus oleraceus)
  • Hog weed/wireweed (Polygonum aviculare)
  • Lesser loosestrife (Lythrum hyssopifolia)

Efficacy can be variable according to climatic and soil conditions. Final use of the product should only be according to the approved label recommendations.

On the label, what weeds will Overwatch®Herbicide label suppress?

  • Barley grass (Hordeum murinum)
  • Wild oats (Avena fatua)
  • Brome grass (Bromus spp)
  • Phalaris (Phalaris paradoxa)
  • Bedstraw (Galium tricornutum)
  • Capeweed (Arctotheca calendula)
  • Prickly lettuce (Lactuca spp.)
  • Wild radish (Raphanus raphanistrum)

Efficacy can be variable according to climatic and soil conditions. Final use of the product should only be according to the approved label recommendations.

Will other crops and weeds be added to the label in the future?

FMC is currently investigating the potential use of Overwatch® Herbicide in several different crops, in different regions across Australia. Through this work we will also be identifying regionally specific weeds that may be added to the label.

How long is the grazing interval on the label?

The label states 12 weeks. However, feeding studies are currently underway to shorten this period so that Overwatch® Herbicide can be used in dual purpose grazing crops.

Is Overwatch® Herbicide (Bixlozone) considered to be a volatile herbicide?

Overwatch® Herbicide (Bixlozone) is not considered to be a volatile herbicide, because:

  1. According to the APVMA, studies indicate that volatilisation and atmospheric transport following application are not likely to be significant for bixlozone*.
  2. Investigations about potential volatility of Bixlozone under controlled conditions in a wind tunnel showed the following:

For an application rate of 300 g Bixlozone®/ha the amount of volatilisation from the application was low (maximum 0.42% at 1 m 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 1 m from the application site. In plants located 20 m 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® Herbicide 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

Is Overwatch® Herbicide fit for commercial launch in Australia?

Yes. Overwatch® Herbicide is 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

Is Overwatch Herbicide prone to drift?

Like every other herbicide, drift from Overwatch® Herbicide 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.

1. 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.

What are the key factors to minimizing drift?

Good spray application management employs a number of techniques to minimise off-target movement.

  • Spray under desirable weather conditions including appropriate temperatures and no inversions
  • Select the correct droplet size
  • Spray when there is a consistent cross wind. Avoid spraying under still
  • Do not spray with the wind direction toward sensitive areas
  • Do not spray when there is excessive wind speed
  • Do not operate with a boom height that is too high
  • Avoid spraying with volatile products

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 above).

Best Management Spray Practices that are recommended for Overwatch® Herbicide are detailed under the Spray Drift Restraints heading on the product label and include:

  • Spray quality should be no smaller than Coarse.
  • DO NOT apply if there are hazardous surface temperature inversion conditions present at the application site during
  • Adhere to mandatory downwind buffer zones specified on the product label

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)

When applying Overwatch® Herbicide, what is the recommended set up of the spray rig?

It is recommended that Overwatch® Herbicide be applied in at least 80 L/ha as a coarse quality spray.

The most preferred application regime for Overwatch® Herbicide also includes:

  • A maximum travel speed of 20 km/hr, preferably 16 km/hr
  • The minimum boom height that still ensures double overlap
  • TeeJet TTI nozzles operated at between 3 and 5 bar and angled backwards to direction of travel to reduce horizontal movement
  • The addition of a drift mitigating adjuvant in the tank mix at label rates will further minimise droplet production and enhance soil deposition

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 the crops recover from bleaching.

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® Herbicide spray drift.

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.

How does FMC impart stewardship information about Overwatch® and other products, and educate users on their appropriate use?

To qualify as a selling Agent for Overwatch® Herbicide, all distributors were required to complete on-line stewardship training on the safe and responsible way to use the product. Agents are expected to impart this knowledge when recommending Overwatch® to growers.

In addition, direct marketing materials, commercial field demonstrations and training modules are being used to educate growers and advisors about Overwatch® Herbicide as well as the appropriate way to use it.

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.

We also encourage customers to reach out to their own agronomists with any questions they may have.
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