The Aclonifen Effect

Ryegrass has consistently been a problem at Littlehales Farm, according to Arable Manager David Pugh. “I’ve been responsible for the arable operation for 11 years. At first, we relied on post-em chemistry, Axial and Pacifica. But about six years ago it was clear we had resistance. One plant would be yellow and dying, but next to it there would be a completely healthy ryegrass plant.”

David Pugh, Arable Manager, Littlehales Farm, Shropshire

“If I’m honest, at first we mismanaged it a little, carrying on the same way and waiting for the next ‘silver bullet’. But four years ago, we got more serious and started using more cultural controls and stacking effective pre-em chemistry.”

Littlehales Farm covers 1500 acres with a further 1600 acres contracted, all with predominantly medium soil. The farm mainly grows combinable crops with a small area rented out for root production. Italian ryegrass is the main problem weed, but there are occasional black-grass patches as well.

 “We have very little black-grass, I believe that it mainly comes in on balers, if we see any plants, we rogue them immediately. The ryegrass problem isn’t terrible, some fields are rogueable, with a spattering of ryegrass, others have more of a problem but are still manageable. Headlands tend to be the main problem areas.”

When the farm first started to get serious about ryegrass control, Mr Pugh a little bit frustrated about how much advice there was out there for black-grass but not for ryegrass.

“Most information was for black-grass control, but we needed to focus on ryegrass. Delayed drilling helps but not to the same degree.”

On farm, they typically cultivate after harvest using a Sumo Quatro before spraying off and then drilling with a low disturbance Horsch Serto. They use variable rate to target weed patches, typically the headlands with 20% more seed.

Cleaner fields are drilled first, starting in late September and continues until the second week of October. “By some standards this is not late-drilling, but we don’t want to lose crop competition. Too much bare earth gives weeds the opportunity to cause problems.”

A robust pre-em stack is a key part of the weed control programme. “Proclus + Liberator + Defy was our pre-em this season. Proclus is definitely adding to the control, it’s hard to put a number on but you can see it. This autumn, we used Alternator Met at early post-em.”

Despite good performance from herbicides, Mr Pugh accepts that the days of the solution coming out of a can are gone. He uses herbicides as management tools alongside cultural techniques and changing cropping.

“We move less soil each season, which definitely helps with weed control. But I don’t think that direct drilling would be right for us as things stand. Straw is taken off the farm and swapped for muck, plus we have our own chicken sheds which also provide manure which needs to be incorporated.”

Removing straw rather than chopping and spreading also causes some compaction that needs rectifying. During the process of moving and loading bales, contractors inevitably stray from tramlines.

Nevertheless, Mr Pugh is keen to experiment and take ideas from regen agriculture to see what it offers the farm. Next season, he plans to look at wider row spacing so he can use an inter row hoe, he has also looked at cover crops but is uncertain how they fit into the system.

“Catch crops don’t appear to be viable with the gap we have between harvest and drilling. I can see cover crops ahead of spring crops possibly offering something for soil health. But we do not grow a lot of spring crops as a rule, our land seems to suit autumn cropping.”

Mr Pugh points out that spring oats, in particular, have been effective at smothering ryegrass so are a good option. He also notes that autumn 2019 meant a lot of enforced spring cropping, which has probably reduced weed burden across much of the farm. Growing beans has also helped, Kerb (propyzamide) does a good job and establishing the following crop of wheat is possible with very little soil movement.

Hand rogueing and topping also help him to keep on top of weeds. The field margins are topped in spring and before harvest to prevent weed seeds being dragged into the field by the combine and grain carts.

Agronomist Tom Pope advises a number of farms in Dorset and Somerset for Agrovista. Although weed problems are fairly restrained, there are a small number of locations having problems with grass weeds.

“Weed problems tend to affect fields rather than whole farms. I advise a lot of land over chalk which is relatively weed free. Black-grass problems are mainly on heavy Somerset clays, but it seems to be slowly spreading to more farms. Some other farms have minor Italian ryegrass problems, and one has some really nasty stuff.”

“Ryegrass has been a problem on the farm for years. Sometimes it gets a bit better, but it seems to adapt to changes in strategy and get worse again. The whole farm isn’t plagued with ryegrass, but it is spreading. The worst field was resistance tested in 2020 which showed resistance to pendimethalin, flufenacet and most post-em chemistry”

The farm grows wheat, barley, oilseed rape and some winter linseed, rye and maize. Cropping is focused on achieving the best margin but the range of crops mean there are good opportunities for cultural control of weeds too.

“There’s also black-grass in parts of the farm that don’t have ryegrass. Overall, the land is quite varied, some of it is at about sea level and other parts are at 300 feet. There is clay but also lots of flint within the soil which limits cultivation options because it wears out equipment so quickly.”

Crops are established with a strip tillage Claydon drill. Winter cereals generally go in from early to mid-October. Mr Pope points out that it can be quite wet and windy in this area so spray timing and application may be difficult. 

“We use robust pre-ems to control weeds in autumn. There are quite a lot of actives available in wheat, so we can get good control, some of the other crops with fewer actives cause more difficulty.”

In wheat, Mr Pope has recommended Liberator + Proclus + Defy with some very pleasing results this season. Avadex is also used on fields with black-grass problems. 

“We first used Proclus against black-grass two years ago, it worked very well, so last autumn it went against ryegrass as well. It worked incredibly well, walking the crops in spring we struggled to find many ryegrass plants even though it was a high-risk field.” 

Despite good results from herbicides, cultural controls are also important. Delaying drilling and to a lesser extent spring crops are valuable tools. Ploughing is also an option when things get very bad. “The field with the very bad resistance test results was ploughed to bury the seed, it was then in stubble turnips followed by maize to try to clean it up.”

Peter Waltham, Agrovista Agronomist

Mr Waltham advises mixed, arable and livestock farmers in Somerset, Dorset and Wiltshire. There are a range of farm and soil types which means a wide range of weeds, but the main problems are familiar to farmers and agronomists across the country.

“Black-grass is the main grass weed problem, but sterile brome, wild oats and ryegrass cause difficulties too. Brome in particular, seems to be becoming a bit more common as direct drilling and no-till increase in popularity.

“When it comes to broad-leaf weeds, we see everything and anything. On the brashier clay soils, charlock, hemlock and cleavers are the main weeds. Poppies and cranesbill tend to cause more problems on the chalky soils in Wiltshire.”

In wheat crops, black-grass control is based on robust cultural controls and autumn chemistry. “We prefer to use residual type chemistry because the control is more consistent with fewer resistance problems than post-ems.”

This season, the standard pre-em has been Liberator + Proclus which is now in its second season. “I first saw it at Agrovista’s Lamport site. You could see an improvement in control compared to other products, so I was keen to use it. So far it is working well, and farmers have been happy about the results.”

He also recognises the importance of using various modes of action in the programme. Many of his customers use Avadex, and he also recommends Octavian for autumn top-ups which brings metribuzin into play.

Overall, Mr Waltham thinks that farmers and agronomists are getting much better at black-grass control, but it is not a problem we will solve completely. “Farmers are now very good at using cultural control such as spring crops, minimal disturbance and delayed drilling. I think they are also more pragmatic; they know it takes more than one season to sort it out. Plus, farmers can still get a good yielding crop with low levels of black-grass, I don’t think that’s a problem as long as they have a plan to keep it under control.”

There is also a greater willingness to manage fields and crops in more detail to solve a problem in a specific field, rather than a farm-wide approach. This is particularly important when deciding how to manage land in those critical weeks between harvest and drilling.

“A lot depends on what weeds you have. Black-grass and sterile brome tend to respond to very light cultivation such as a straw rake to encourage a chit to spray off. Wild oats are probably best left on the surface, burying means they’ll cause problems later.

It’s all about a tailored approach. The most important thing is to ask what are you trying to achieve and how are you going to do it. This will be different depending on the field, following crop and so on. I am expecting a higher number of second wheats this season, which isn’t a problem for weed control, but these fields are best drilled later.”

Jonathan Guy, ProCam agronomist, South Yorkshire.

ProCam agronomist Jonathan Guy advises farms across South Yorkshire. Both black-grass and Italian ryegrass cause problems in his area, but on balance, ryegrass is more troublesome to control.

“A lot of ryegrass seems to be nigh on impossible to control in a cereal crop. Spring cropping is very effective against high black-grass populations but often not for ryegrass. It can still germinate and produce a large infestation in a spring barley crop.”

“Over the last few years, I have had resistance tests done on some difficult to control ryegrass across the county. Most samples came back showing RRR resistance ratings for contact-acting herbicides, and resistance to residual chemistry flufenacet and prosulfocarb too. This meant I had to look at something else to get good pre-em control of ryegrass. Darren Adkins of Bayer suggested using Proclus (aclonifen) in the mix with Liberator (flufenacet + diflufenican) which had given good results on ryegrass in other parts of the country.”

“Autumn 2021 was my first year using Proclus. The results overall have been good and it has certainly helped control ryegrass, but seedbed quality has also been really important in order to get the benefit. The ryegrass has to grow through a layer of aclonifen on the soil surface which means the ground needs to be even, without lots of clods and consolidated for maximum product efficacy.”

“Another thing to watch is heavy rainfall just after application. In general, I would say you have to be more careful than just using Liberator. Proclus is pre-em only, so the sprayer needs to be chasing the roller after the drill so that it is applied at the right time.”

So far, Mr Guy has not used Proclus against black-grass because cultural controls and existing autumn stacks and sequences are still working well. “I haven’t used it for this, but I know of people getting good results with it.”

“For grass weeds it is cultural control first and out of the can last. Spring cropping and delayed drilling work for black-grass. To deal with ryegrass, I recommend paying attention to the stale seedbed. Create a stale seedbed as if you were sowing a grass ley, use a roller to consolidate and promote maximum germination before drilling.”

“It all works well in theory, but moisture levels can be a problem. Dry Septembers seem to be quite common, which means you must wait until rain for germination, however once it starts raining in late September / early October, drilling starts and ryegrass ends up emerging with the crop; this is where the advice and the practicality break down. There’s no simple answer. Know what resistance levels you are dealing with, but have a back-up plan, to accommodate whatever the weather throws at you.”