Teaming pre-emergence sprays with a residual herbicide adjuvant offers pulse growers the best chance of keeping yield-robbing weeds at bay ahead of the spring, according to the latest advice from Interagro.

A small break in the weather has no doubt left sprayer operators up and down the country raring and ready to get going with spring applications. However, with the longer-term forecast looking typically inclement, spray windows could once again be tight – leaving crops exposed to the threat of weeds.

Unlike cereals and oilseed rape crops which are considered fairly competitive, pulse crops are highly susceptible to weed competition in the early stages. With associated yield losses of up to 40% and a very limited herbicide armoury post-emergence – mainly bentazone – achieving the best results possible from pre-emergence applications is crucial for the strong weed free start that is required, explains Stuart Sutherland, technical manager at Interagro.

“Weed control is one of the biggest challenges for pulse growers, so getting the strategy right is vital for maximising returns. Having come out of a really bad autumn and winter period, workload pressures will add to the challenge this spring, however, there are a few vital quick wins growers can achieve simply by incorporating a residual herbicide adjuvant.”

Backrow Max, from Interagro, is among the offerings on the market, which is claimed to minimise drift, increase coverage and maximise uptake of pre-emergence herbicides.

On target applications

Delving deeper into the benefits, Stuart says that Backrow Max’s ability to minimise spray drift avoids both off-targeting and under-dosing crops. “The first port of call to minimise drift is often using drift reducing nozzles, but the inclusion of Backrow Max will optimise the application even further by reducing the number of <100 microns droplets which are the most susceptible to drift.”

With pulses particularly vulnerable to weed competition, good even coverage is crucial to create a robust herbicide barrier to block germinating weeds, continues Stuart.

“Misses in coverage will allow weeds to find a way through. This can be particularly problematic with faster forward speeds, low water volume spraying, and using drift reducing nozzles because they create coarser droplets.

“Including Backrow Max will help because, as well as reducing the number of very small droplets prone to drift, it also reduces the number of very coarse droplets prone to run-off, resulting in a more optimal droplet size for pre-em application.”

Keeping in the “kill zone”

Backrow Max also brings herbicide retention benefits – vital for helping keep products in that crucial top 5cm. “After an exceptionally wet autumn and winter, saturated soils could be holding on to water for some time — even if they dry out nearer the surface and are okay to travel on,” says Stuart.

“In these conditions, herbicide retention in the top 5cm – the weed germination zone – could be compromised, because herbicide mobility in the soil profile increases with higher moisture levels. Heavy rainfall events after herbicide application to wet soils will have the biggest impact.”

Herbicide active ingredients with high mobility and low soil adsorption properties – imazamox and clomazone – will be the most vulnerable, he adds. “In the worst-case scenario, herbicide may leach to the crop seed, damaging the emerging pulse seedlings.”

Research shows Backrow Max is one, if not, the most effective residual herbicide adjuvant at improving herbicide retention in the weed zone, increasing residual activity, believes Stuart. “This will be crucial in situations where several flushes of weeds are expected, where herbicide half life is short – for example with prosulfocarb-based products – or where weather conditions remain volatile during crop establishment.”

Maximal uptake

This improved retention goes hand-in-hand with maximised uptake of herbicides – another area in which Backrow Max has been proven to aid. “On the lighter soils, it’s not inconceivable to imagine that with a period of prolonged dry weather, seedbeds could suddenly turn drier than is ideal for optimum herbicide efficacy,” explains Stuart. “Herbicides with low mobility and high adsorption to organic matter will be most susceptible to the effects of low moisture – they need more moisture to be displaced from soil organic matter for uptake to occur. Actives most at risk here will be pendimethalin and aclonifen.

“If it’s too dry for weeds to germinate then it’s worth considering postponing the application until rain is forecast, unless you are using a herbicide with a longer half-life that will remain active in the soil – such as pendimethalin – which will be ready to work when weeds germinate.”

Stuart says that Backrow Max can add as much as 33% efficacy in dry conditions slowing the drying process and keeping the actives working longer. This has been proven in controlled lysimeter studies in the Netherlands where Backrow Max increased moisture levels by 30%.

“In replicated field trials in spring beans, Backrow Max added 33% efficacy to Stallion (prosulfocarb + pendimethalin) against black bindweed, and 19% to blackgrass control.”

Strategies for success

As the picture for March looks largely unsettled at present, planning ahead and taking action ahead of the game, where possible, will be vital this spring, concludes Stuart. “If we’ve learnt anything from the past few years, it’s how quickly things can change. While things are looking pretty damp and miserable at the moment – despite a recent break in the weather – we know just how quickly this could change and it may not be long before we’re talking about a spring drought again.

“Pulses are becoming increasingly important crops in the rotation, but they come with risk, so by utilising all the tools and strategies in the armoury – including pairing products with a proven, scientifically backed adjuvant like Backrow Max — is going to be vital for getting the most out of them.”

About Backrow Max

Backrow Max is a residual herbicide adjuvant approved for use in an extensive list of crops.

You can find out more about it by downloading Interagro’s latest brochure here: https://www.interagro.co.uk/wp-content/uploads/2023/11/Backrow-Max-Booklet.pdf