Innovation Insight – Liquid logic has a way with weeds

When Dupont scientists finally created a formulation to partner fluroxypyr with sulfonylurea herbicides, it wasn’t just the spectrum of the one-can solution that was improved. CPM tells the story.

The improved adjuvant properties of the oil dispersion formulation resulted in better weed control.

By Tom Allen-Stevens

Sulfonylurea herbicides have long been the mainstay of broadleaf weed control in the spring. Low dose rates and a broad spectrum make them a farmer friendly addition bringing cost-effective, season-long control of a number of culprits that perennially slip through the net cast by the autumn residual herbicide.

But there have always been a couple of niggles with them – cleavers aren’t controlled by the majority of SUs used in the spring, and then there’s the bewildering restrictions on sequencing and mixtures.

“When autumn residual herbicides start running out of steam we see problems with broadleaf weeds,” notes Steve Cook of Hampshire Arable Systems. “And by May weeds are often large so sulfonylureas can struggle to provide satisfactory control, especially of charlock and cleavers which keep emerging throughout the season.

“We have the option of going back in with Starane (fluroxypyr) for cleaver control, but there are other weeds to consider too, so a product with a broader spectrum is needed.”

There are also restrictions on mixing and sequencing acetolactate synthase (ALS) chemistry, he notes, and this can be a problem, especially for growers where blackgrass is a target.

“Until now, a maximum of two applications of ALS herbicides within a season have been allowed, which has restricted the choice of a spring herbicide when flupyrsulfuron (FPU) and Atlantis (iodosulfuron+ mesosulfuron) had been used as part of an autumn grassweed strategy,” he explains.

For Scottish agronomist Iain Learmonth, the ability to successfully control aggressive populations of cleavers and groundsel and potentially ALS-resistant populations of chickweed and mayweed, has become even more important. He advises for Gardiner ICM, consulting on over 9000ha of a fertile ribbon of land stretching from just North of Aberdeen to the Black Isle.

Dupont trials in Lincs in 2015 show the efficacy of Provalia LQM on cleavers (left) compared with straight fluroxypyr at 135 GAI/ha.

Winter cereals constitute the bulk of his cropping with oilseed rape and potatoes as a break. While pre and early post-emergence herbicides have afforded satisfactory control, there are limited opportunities to use these, and weeds such as chickweed often slip through the net.

““I often find myself recommending an extra application after growth stage 32 to clean up the crop,” he says.

Weeds such as pansy, hemp nettle, mayweed and polygonums are perennial challenges for him. “SUs are very useful at what they do, if used sensibly, in terms of the broad spectrum of activity they have and their ease of use – if you apply an SU, you can usually be confident you’ve plugged any gaps.”

Performance in marginal conditions

The SU herbicides were introduced in the mid-1980s. It was a Dupont scientist, George Levitt, who first managed to capture the high potency from extraordinarily low dose rates certain compounds within this class of chemistry could exhibit. He persisted in synthesising new molecules long after other chemists had abandoned the SUs, and helped to bring actives such as metsulfuron-methyl, tribenuron-methyl and thifensulfuron-methyl (as in Ally Max SX and Harmony M SX) to market.

Dupont has continued to develop the chemistry, improving the formulation and the spectrum of weeds controlled by this remarkable low-dose class of molecules. But for the past 30 years, there’s been a recognised challenge the research team has sought to overcome. “We haven’t had a cleaver solution,” notes Dr Tim Obrigawitch, global technical product manager for Dupont at its main facility in Newark, USA.

“What we’ve been looking for is a product that would provide a broadleaf-weed solution in just one package. The other aspect to address with this class of chemistry is that it relies on one mode of action. The difficulty has always been with the formulation.”

Fluroxypyr, also introduced in the mid-1980s, has long been the product of choice for cleaver control. It’s a synthetic auxin with a high degree of activity and selectivity for the weed.

“Fluroxypyr is a liquid formulation. For a one-can solution, we needed to find a liquid SU formulation we could tank-mix. But the main stumbling block has always been that SUs can lose their stability in a liquid – that’s why you should never leave them in a spray tank for a long period of time,” explains Tim Obrigawitch.

Provalia LQM weed spectrum

Many hundreds of different formulations have been tested and millions of dollars spent searching for the answer, he says. “It’s eluded us for the past 27 years, but eventually in 2013, we cracked it – we developed an oil dispersion (OD) formulation that could take metsulfuron, stabilise it with other SUs and fluroxypyr and that could be used at the right rate.”

It was the first time that such a combination had been made possible. But it was only during field testing that all of the benefits of the new technology emerged. “We’d aimed for a product that was stable and easy to apply. It also had to be compatible with a wide range of tank-mixes, including liquid fertiliser, without foaming and be suitable for use on winter cereals. All of these we achieved,” continues Tim Obrigawitch.

“But what we noticed in the field was better spreading and adhesion to the leaf with this product. The improved adjuvant properties of the oil dispersion formulation resulted in better weed control.”

It was launched first to Canadian farmers in 2015. “It was a huge success – many of them prefer a liquid formulation and had been looking for a one-can solution. But the market there is mainly for spring cereals.”

In Europe, the new formulation is branded as LQM, and the UK growers are set to receive it first this season, following its approval for use late last year – it’s due for commercial roll-out across other EU countries in 2018.

Provalia LQM combines metsulfuron-methyl, thifensulfuron-methyl and fluroxypyr into the oil dispersion formulation. It’s cleared for use in winter wheat and winter barley from 15 March, or GS21 up to GS39. Available in a five-litre pack, the maximum dose is 1 l/ha, which will deliver 5g/ha, 30g/ha and 135g/ha of the three actives respectively – roughly equivalent to mixing Harmony M SX with Starane.

“But the new formulation outperforms the same products if you just tank-mix them,” notes Dupont cereal product manager Alister McRobbie. “Its real strength is in marginal conditions, so you can apply it earlier in the season when it’s cold. But equally, at the other end of the season, it performs well on larger, over-wintered weeds – better than the current SU chemistry.”

Dupont trials from 2012-2015 have shown Provalia at both full and three-quarter rate outperforms fluroxypyr alone against cleavers, and it sits well ahead of florasulam plus fluroxypyr. Studies with pot-grown cleavers under controlled conditions of 5-12°C have also shown improved control of Provalia ahead of competitor products (see chart above).

Another key difference with Provalia is there’s more flexibility with ALS sequences, adds Alister McRobbie. “Up to now, growers could only sequence two ALS herbicides on a crop. With Provalia, they can use it in sequence on crops where both FPU and Atlantis have been used previously in autumn programmes for control of bad blackgrass – a real improvement in flexibility for growers and agronomists.”

Provalia also boasts an impressive weed spectrum, he points out (see table above), which takes in polygonums and volunteer oilseed rape. “The fluroxypyr also adds another mode of action against chickweed, where resistance may be an issue.”

Iain Learmonth used Provalia in trials last year in both winter wheat and barley. “It’s not a game-changer, but it does improve efficacy, particularly on substantial winter-hardened and normally difficult to control cleavers, chickweed and groundsel. It’s a particularly convenient and flexible formulation as well.

“It won’t be used exclusively, but prescriptively and well targeted applications from GS32-39 will mean that the headache of dealing with those aggressive and hugely competitive populations that have slipped through the autumn herbicide net, can be dealt with effectively.”

Steve Cook has also seen the efficacy of Provalia in last year’s trials and reckons it shows impressive knock down of most of the key broadleaf weeds. He notes there’s a quicker activity on both small and larger weeds, over a broader spectrum of species. “It picked up some weeds not adequately controlled before, such as speedwell and wild carrot.

“It’s not just about improved weed control, though – Provalia isn’t new chemistry, after all. What it offers is a new formulation of actives that we haven’t had before. So it’s the one-can solution, easier mixing and three-way sequencing with other ALS herbicides that’ll be of benefit. It just makes the job of controlling broadleaf weeds in spring that much simpler,” he concludes.

Weed control boost from formulation fervour

The new LQM formulation in Provalia has some unique characteristics that alter the way it lands on the leaf, remains there and is rapidly taken up by the plant, points out Alister Mc Robbie.

“Spray droplets that have a high dynamic surface tension (DST) will tend to bounce or run off the leaf surface,” he explains. “Tests have shown Provalia has a lower DST than either the tank-mix equivalent or competitor products. Droplets remain on the leaf surface which mean the maximum surface area comes in contact with the leaf and as a result, you get maximum AI uptake.”

A key point to note is that this isn’t about rainfastness, but enhanced uptake, he adds. In another test, pansy plants were treated with Provalia and the tank-mix equivalent. The leaves were then washed using a solvent – some after 30mins and some after four hours. Plants were then assessed 14 days after treatment.

“After just 30mins, much more AI was taken up by the plant in the LQM formulation, compared with the SX tank-mix. We found similar results with competitor products and with other weeds.”

For best results, he recommends growers target weeds when they’re small and actively growing. “However, because of the new formulation, a full wash-out procedure is required,” he notes.

New solution sought for tough weeds

Weeds that are proving to be increasingly tough to control in winter cereals are persuading Oxon grower Philip Barber to change his approach.

“Wild carrot in particular is becoming a problem,” he notes. “It may be that we underestimated in the past just how much of a good job the old autumn-applied chemistry did. But we’re now finding you need broadleaf-weed control in the spring you can rely on.”

Resistant blackgrass dictates much of the herbicide programme across the 445ha of arable crops Philip Barber grows, based at Friars Farm, near Witney. Clay over gravel gives him ground that can lie waterlogged in the winter but is drought prone during summer months.

“We won’t start drilling cereals until mid Oct, and these will always receive a pre-emergence herbicide of flufenacet and pendimethalin, with a bit of diflufenican. We’ll then follow up post emergence with flufenacet to bring it to the full rate for the season, with some extra DFF or PDM. It’s then a question of wait and see what comes through in the spring.”

Despite a pretty robust autumn stack, he’s finding an extra application of spring herbicide is a regular requirement. “Cleavers will often germinate, but wild carrot is also becoming an increasing problem. You see it in early spring, and if you don’t deal with it, you’ll have large plants competing with the crop – it grows fast,” notes Philip Barber.

“I’ve tended to deal with it at the T0 timing, and sometimes risked going as late as T1. I’ve found full rate Ally Max SX (metsulfuron-methyl+ tribenuron-methyl) is the only herbicide that’ll touch it. But you still have to come back with something for the cleavers.”

This year, he’s planning to try Provalia. “It’ll be interesting to see how it does on the wild carrot. I understand it’s faster acting and will take care of the cleavers. It’s a liquid, that makes things easier. But the nice thing is that it’s a one-can solution that’ll take care of a very specific weed issue I have,” he notes.

Innovation Insight

CPM would like to thank Dupont for kindly sponsoring this article, and for providing privileged access to staff and material used to help put the article together.