A star is born: Or so Dow AgroSciences would like growers to believe. Broadway Star, a new graminicide, is, according to its manufacturer, as good as Axial, Topik and Atlantis on wild oats, better than the latter and the specific brome killers on bromes, and generally speaking better than Axial on ryegrass.

Not a bad resume. And then you can add a much wider range of broadleaved weeds to its spectrum than any of those products, plus no following crop or cultivation restrictions – an issue for some Atlantis users, in particular.

So far, so good. But there are a couple of issues that might restrict its market, at least initially. The first is that for all that wide weed spectrum, the gaping hole is blackgrass. While it has some effect it is not good enough, like Axial, for it to be considered worthy of a label claim. That means it should only be used in single or mixed grassweed situations where blackgrass is not an issue.

Resistance

Its ALS inhibitor mode of action is the same as sulfonylureas, such as Atlantis, which means that restrictions imposed to delay resistance building to the chemistry apply to Broadway Star, and it cannot be used in mix or sequence with any other grassweed active ALS inhibitor. That rules it out, unlike Axial, being used in the spring to tidy up non-blackgrass grassweeds following Atlantis applications.

Additional resistance management restrictions put in place on Broadway Star’s label might also cause some growers and advisers some issues. A key one is that it must be used as part of a programme targeted at grassweeds, including the use of an appropriate pre- or peri-emergence residual herbicide, the use of residual partner products and follow-up graminicides with a different mode of action where appropriate.

Following those guidelines is a regulatory requirement, stresses Dow’s James Knight. “It is part of the approval. If you haven’t used a residual programme, then you shouldn’t be using the product. It would be against the label and the product’s conditions of use.”

Relaxed restrictions

In most years the programme shouldn’t be much of an issue, particularly for ryegrass and bromes. But this season hasn’t been “normal”. Some planned residual treatments did not get sprayed, for example. That does make it tricky, although not impossible, for Broadway Star applications this season, Mr Knight admits.

Dow has relaxed the restrictions, for example, where wild oats are the only target. Its recommendation had been for full rate pre-treatments of residuals, such as Crystal or Liberator, or robust Defy mixtures – something most growers would struggle to meet in any season.

Alternative strategies using lower rates of residuals are being developed but for this year Broadway Star will be allowed, for wild oats only, to be used where no pre-treatment has been applied, providing the farmer or agronomist commits to checking the field that it has controlled everything, Stuart Jackson, Dow’s technical specialist says.

“If there are any survivors or new germinators then he has to apply a fop, dim or den herbicide to take them out. Provided everything is controlled there cannot be any resistance build up.”

Pre-treatment

The other condition is that the wild oats aren’t resistant to fop or dims. “In that case if there are any survivors he wouldn’t have anywhere to go, and would need to have a residual on before Broadway Star.”

Where no pre-treatment has been applied it is really important to take out weeds of the correct growth stage as soon as conditions allow. In a trial, where the wild oat population was predominantly autumn germinating, there was a clear yield penalty from leaving control until well into the spring, Mr Jackson says.

“The best yields, although not necessarily the best control, came from autumn applications, followed by early spring treatment.”

But applying the base treatment gave much more flexibility in timing, he notes. “If you put the base treatment down, yields were similar regardless of treatment date. It took the competition away, and gives you more flexibility when to treat.”

The trial highlighted the importance of both the pre-treatment, and also that ALS inhibitors, like Broadway Star, are better targeted earlier in spring rather than late, he says. “Growers tend to leave Atlantis late to try to get everything, but end up not doing anything at the optimal time. It also helps to protect yields.”

Brome control

Sterile or great brome must be treated in the autumn. Where that is the primary target Dow recommends a tank mix with 1000g ai/ha of pendimethalin – following a pre-emergence spray. “In trials we achieved 94% control from autumn sprays compared with 70% from spring treatment. That leaves 30% potentially going to seed after being exposed to the product. We’re concerned that could lead to resistance developing quickly.”

Meadow, rye and soft brome can all be treated in the spring, he notes.

Application advice

Broadway Star is a contact herbicide that needs active weed growth for best results, Mr Jackson says.

Like grassweed sulfonylureas its performance is affected by cold weather slowing or stopping weed growth, so he recommends it is only applied when there are clear signs of active growth, such as a new leaf emerging or, more crudely, when the lawn needs cutting. Timing trials have also suggested best results from when soil temperatures are 8C or above at a 10cm depth.

It is also crucial for spray quality to be fine, or on the finer side of the medium spectrum. “At the moment we are recommending a conventional flat-fan nozzle at 130-150 litres/ha water volume to provide the best combination of droplet size and coverage.

“But you can go down to 100 litres/ha providing the crop or weed density is not too great.”

Air induction or low drift nozzles are not recommended. “Anything that increases droplet size giving less contact points and less coverage is not recommended.”

More data are also required before the firm could recommend using newer nozzle technology, such as the Hawk nozzle, he adds.

Adding an adjuvant is also critical to performance. A range, including Abacus, Activator 90, Drill, Kinetic and Torpedo, are recommended. The only thing they have in common, apart from performing similarly, is they have the least impact on droplet size when they are put through a nozzle, Mr Jackson explains.

Active Ingredients

• Broadway Star – florasulam + pyroxsulam
• Atlantis – mesosulfuron-methyl + iododsulfuron-methyl-sodium
• Axial – pinoxaden
• Topik – clodinafop-propargyl
• Crystal – flufenacet + pendimethalin
• Defy – prosulfocarb
• Liberator – flufenacet + diflufenican