Largest UK weed survey reveals Italian ryegrass challenge

Farm Weekly

© Blackthorn Arable

Results from the UK’s largest survey on Italian ryegrass has shown a complex and variable picture of herbicide resistance in the weed, emphasising the need for growers to test and understand the populations on their farms to achieve better control.

However, rising levels of resistance to commonly used herbicides are not the only cause of control difficulties, reveals weed specialist John Cussans of Niab, who also highlights application timing and better use of diversified modes of action as important actions.

See also: Tips on tackling five weed issues in no-till systems

“There is scope to improve practice, as there are too many fire brigade treatments being made,” he advises.

“It’s a complicated landscape when it comes to resistance mechanisms, but better attention to detail will help to avoid poor decision-making.”

Conducted by Niab with funding from Bayer, the survey of 197 samples from across the country investigated current on-farm control practice, as well as testing each Italian ryegrass sample for sensitivity to flufenacet, pinoxaden (Axial) and ALS herbicides (Atlantis).

In addition, 22 of the weed samples were used in a cross-resistance study, to understand any correlations between sensitivity to a wide range of herbicides, including glyphosate.

Post-emergence herbicides

“While the performance of post-emergence herbicides is significantly affected by resistance, it was lower than expected,” says Mr Cussans. (see “Post-emergence herbicide sensitivity”)

“The fact that a large number of samples are still susceptible to herbicides goes against the perception that many have about post-emergence chemistry.”

Dropping the use of perfectly good herbicides tends to happen when the resistance threat is exaggerated, he explains, which is why a better understanding of the situation on individual farms is so important.

Pre-emergence herbicide

When it comes to pre-emergence herbicides, all 197 samples were tested for sensitivity to straight flufenacet.

One-third of them showed either reduced sensitivity or resistance, reflecting that the selection pressure has been there for some time.

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“If you pile on flufenacet, you will select resistance to it,” he says. “Of course, in practice it isn’t used alone – it is tank-mixed and sequenced with other actives.”

There are some populations of Italian ryegrass that are completely resistant to flufenacet – which makes it different to the situation with blackgrass, where there has been a shift in sensitivity, rather than complete failure.

Post-emergence herbicide sensitivity (% of samples)
	Atlantis	Axial
S	45.6	45.6
R	7.7	6.2
RR	24.1	32.3
RRR	22.6	15.9

Pre-mergence herbicide sensitivity (% of samples)
	Flufenacet
Sensitive	70.6
Significantly Reduced	17.3
No Control	9.6

Resistance testing

Further analysis showed regional differences between the three herbicides tested, with control from flufenacet being lower in the South East, North and Midlands.

“If you have an emerging issue with pre-emergence herbicides, you need to know about it. Get resistance testing done, preferably on a field-by-field basis – national statistics will make no difference to managing your weed populations.”

Even populations collected from two fields on the same farm can show differences in herbicide sensitivity, he warns, reflecting the very variable herbicide sensitivity present around the country.

Cross-resistance findings

A subset of 22 populations was used to test more herbicides and understand any correlations between them, as well as to look at glyphosate sensitivity.

The strongest correlation is between the existing pre-emergence actives – flufenacet, pendimthalin and prosulfocarb – while aclonifen is weakly correlated with sensitivity to existing pre-emergence products.

“If you have flufenacet resistance on the farm, you need to bring in other modes of action,” advises Mr Cussans. “Where three actives are combined, such as Liberator + Proclus, it largely overcomes flufenacet resistance.

“Broadening the base by combining modes of action helps to stabilise ryegrass control. That fact that we have two new modes of action this year in aclonifen and cinmethylin, and another coming next year, will help.”  

Having a stronger, more diverse base for Italian ryegrass control is important, he stresses.

“Ryegrass is more capable of overcoming herbicides and we know there is a degree of cross-resistance between existing pre-emergence chemistry.

“For this reason, it’s important to combine modes of action.”

Glyphosate sensitivity

There has been a shift in sensitivity to glyphosate in some problematic UK Italian ryegrass populations, but it is not resistance, confirms John Cussans.

The status of 50 difficult weed populations collected in 2019 was checked for their sensitivity to glyphosate at a range of doses, with some variation showing.

“We do not have glyphosate resistance in the UK, but we are as close as we’ve ever been to it,” he cautions. “That’s why we must monitor it and steward the product.”

Glyphosate sensitivity is totally independent of in-crop herbicide use, with the correlation between glyphosate sensitivity and sensitivity to other herbicides being very poor.

However, there is no doubt in Mr Cussan’s mind that poor practice will lead to glyphosate resistance, as it has been possible to select for glyphosate resistance in high-risk scenarios in glasshouse work.

“We must avoid any survivors of glyphosate applications going on to set seed.”

As a result, growers must take ownership of this issue and follow published guidance, he advises.

That is a view shared by Roger Bradbury, technical specialist at Bayer, who stresses the need to apply glyphosate at the right time, with the right dose for the target weed and with good application technique.

He refers growers to the latest Weed Resistance Action Group guidelines, which recommend a maximum of two glyphosate applications after harvest, before drilling the next crop, and stress the importance of monitoring herbicide performance and investigating any reasons for poor control.

“Everyone needs to be aware of the risks and do all they can to prevent resistance to selective herbicides.”

Aclonifen approval in barley

Bayer’s Proclus (aclonifen) has been approved in a tank-mix with Liberator (flufenacet +  diflufenican) for pre-emergence weed control in winter barley, adding a new mode of action and expanding the options for grassweed control in the crop.

A lower application rate of 1 litre/ha + 0.6 litre/ha Liberator, compared with 1.4 litres/ha in winter wheat, means the levels of weed control are slightly less – with a 7% uplift in Italian ryegrass recorded in Bayer trials and a 5-6% improvement in blackgrass control.

Winter barley’s earlier drilling date and more limited herbicide choice can make it a challenging crop for weeds, says Bayer’s Tom Chillcott, who points out that including aclonifen in the pre-emergence mix gives more protection and helps with resistance management.

“Having a new mode of action in barley adds another layer of protection and helps to take the selection pressure off flufenacet.”

As aclonifen sits on the soil surface, weeds have to grow up through it before it takes effect, he adds.

“That means seed-bed preparation, drilling depth and application timing all matter, especially as aclonifen can be a bit hot in some scenarios, and barley is a more sensitive crop.”

A minimum sowing depth of 3.2cm and application within 48 hours are important, as is avoiding heavy rain soon after application.

It will be sold as a co-pack of Proclus and Liberator, as in wheat, and will add £10/ha to pre-emergence costs in barley.

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India gets first herbicide-tolerant & non-GM rice varieties; launch today

Indian Express, Oct. 19, 2021

The varieties — Pusa Basmati 1979 and Pusa Basmati 1985 — contain a mutated acetolactate synthase (ALS) gene making it possible for farmers to spray Imazethapyr, a broad-spectrum herbicide, to control weeds.

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Written by Harish Damodaran | New Delhi |
Updated: September 28, 2021 7:37:06 am

IARI director AK Singh at a trial field containing both herbicide-tolerant basmati and normal basmati (left plot), whose plants have been killed along with weeds after spraying Imazethapyr. (Photo by Harish Damodaran)

The Indian Agricultural Research Institute (IARI) has developed the country’s first-ever non-GM (genetically modified) herbicide-tolerant rice varieties that can be directly seeded and significantly save water and labour compared to conventional transplanting.

The varieties — Pusa Basmati 1979 and Pusa Basmati 1985 — contain a mutated acetolactate synthase (ALS) gene making it possible for farmers to spray Imazethapyr, a broad-spectrum herbicide, to control weeds. This dispenses with the need to prepare nurseries where paddy seeds are first raised into young plants, before being uprooted and replanted 25-35 days later in the main field.

The two new varieties are scheduled to be officially released by Prime Minister Narendra Modi on Tuesday.https://56428c50993d1e8aab4b4fb64a9125c7.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.htmlRead |Need to think of ‘respectable jobs’ for landless and small farm households: NITI Aayog member

Paddy transplantation is both labour- and water-intensive. The field where the seedlings are transplanted has to be “puddled” or tilled in standing water. For the first three weeks or so after transplanting, the plants are irrigated almost daily to maintain a water depth of 4-5 cm. Farmers continue giving water every two-three days even for the next four-five weeks when the crop is in tillering (stem development) stage.

“Water is a natural herbicide that takes care of weeds in the paddy crop’s early-growth period. The new varieties simply replace water with Imazethapyr and there’s no need for nursery, puddling, transplanting and flooding of fields. You can sow paddy directly, just like wheat,” said A K Singh, director of IARI.Top News Right Now

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Imazethapyr, effective against a range of broadleaf, grassy and sedge weeds, can’t be used on normal paddy, as the chemical does not distinguish between the crop and the invasive plants. The ALS gene in rice codes for an enzyme (protein) that synthesises amino acids for crop growth and development. The herbicide sprayed on normal rice plants binds itself to the ALS enzymes, inhibiting their production of amino acids.

The new basmati varieties contain an ALS gene whose DNA sequence has been altered using ethyl methanesulfonate, a chemical mutant. As a result, the ALS enzymes no longer have binding sites for Imazethapyr and amino acid synthesis isn’t inhibited. The plants can also now “tolerate” application of the herbicide, and hence it kills only the weeds.Also Read |India must shed obsession with ‘marginal farmers’. Their future lies outside farms — in dairy, poultry, food retail

“This is herbicide-tolerance through mutation breeding, not GM. There isn’t any foreign gene here,” Singh pointed out.

Both Pusa Basmati 1979 and 1985 have been bred by crossing existing popular varieties — Pusa 1121 and Pusa 1509, respectively — with ‘Robin’. The latter is a mutant line derived from Nagina 22, an upland drought-tolerant rice variety. The mutant was identified for Imazethapyr-tolerance by S Robin, a rice breeder from Tamil Nadu Agricultural University in Coimbatore.Also Read |For easy access to schemes, Govt plans 12-digit unique ID for farmers, database

Farmers in Punjab and Haryana are already adopting direct seeding of rice (DSR) in response to labour shortages and depleting water tables. This year alone, roughly 6 lakh of the total 44.3 lakh hectares area under paddy in the two states has come under DSR.

DSR cultivation is currently based on two herbicides, Pendimethalin (applied within 72 hours of sowing) and Bispyribac-sodium (after 18-20 days). As Singh pointed out, “These are costlier than Imazethapyr (Rs 1,500 versus Rs 300/acre). Imazethapyr, moreover, has a wider weed-control range and is safer, as the ALS gene isn’t present in humans and mammals. Even in the herbicide-tolerant rice, the chemical will target only the weeds.”

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Transplantation in paddy typically requires about 30 irrigations, each consuming some 5 hectare-cm of water (one hectare-cm equals 100,000 litres). Puddling alone takes up about 15 hectare-cm. In all, DSR is estimated to need 30 per cent less water, save Rs 3,000 per acre in transplantation labour charges, and also 10-15 days’ time due to no nursery preparation.

But DSR’s success hinges on an effective herbicide solution — like breeding Imazethapyr-tolerant varieties.

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Pigweed shows resistance in spots to glyphosate, ALS, HPPD and PPOs

Eric Jones/NCSUWes Everman urges farmers to be on the lookout for water hemp on their farms.Everman stresses the importance of pre-emergent herbicides, postemergent herbicides and residuals.

John Hart | Aug 24, 2021SUGGESTED EVENT

Farm Progress ShowAug 31, 2021 to Sep 02, 2021

North Carolina State University Extension Weed Specialist Wes Everman continues to urge North Carolina farmers to be on the lookout for resistant waterhemp, redroot pigweed and Palmer amaranth across the state.

Speaking at the Blacklands Farm Managers Tour Aug. 4 at Turnpike Farms in Pantego, N.C., Everman said Palmer amaranth is now showing resistance in spots across North Carolina to glyphosate, ALS, HPPD and PPO technologies. He noted that testing is also underway to see if Palmer amarnath is resistant to atrazine. He also said resistant redroot pigweed is popping up in spots across the state. https://dc33b5251deac1ea475e6c827fe410e1.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Once again, Everman urged farmers to use multiple modes of action as the key to resistance management. He stressed the importance of pre-emergent herbicides, postemergent herbicides and residuals.

“I see folks going out with jut 2,4-D, just dicamba, or just Liberty with no residual in the tank, no other  product in the tank. That’s a recipe for disaster,” Everman told the crowd at the Blacklands tour.

Everman noted that when one product quits working, farmers shift to another and then switch again and switch again. “We don’t get away from resistance by doing that. We want to use these residuals, our Group 15s, Dual, Warrant, Zidua, and our Group 14s, Valor, Spartan and Reflex.”ADVERTISING

The use of both pre-emergence and postemergence herbicides is a must. He said such products as Flexstar, Cobra and Blazer can generally be used across the farm. He also said metribuzin is generally a safe option as well. He stressed the importance of rotating Liberty, Enlist and Xtend traits.

“If we can rotate them in a season, even better. We can’t just pick one technology and wear it out and then hope to go to the next. I don’t think that’s going to work, and we’re only talking about three products. How long do we have if we don’t start switching now?” Everman said.

Everman pointed out the new weeds are coming into the state primarily through equipment that is purchased from Midwestern states and then brought into North Carolina. He also said waterfowl can move weed seed from one part of the state to another. He said it has been confirmed that water hemp was introduced into North Carolina from a combine purchased in the Midwest and brought to North Carolina.

He urged farmers to be on the lookout for water hemp on their farms. It is different than Palmer and redroot pigweed in that it has thin leaves and shorter petioles. He said it is hairless, like Palmer.

“If you have a weed that looks like it might be Palmer, but looks a little funny, get in touch with your county agent or Charlie (Cahoon, also a North Carolina State Extension weed specialist) or me. We want to make sure. We don’t want to see water hemp pop up in too many places,” Everman said.

In addition to keeping an eye out for water hemp, redroot pigweed and Palmer amaranth, Everman urged Blackland farmers to be on the lookout for common ragweed. He said just north of the Blacklands, in northeastern North Carolina, common ragweed has shown three-way resistance to glyphosate, ALS and PPO inhibitors.

“It (common ragweed) could move on equipment down here. Water hemp came to North Carolina from the Midwest. Pretty much everything we have identified in North Carolina has moved on equipment. They brought it here and they brought along seed issues,” he said.

“The No. 1 piece you can move weed seeds with is a combine. If you have a weedy patch, if you’re bringing a combine from another farm, if you’re getting help from somebody, if you have time and you have the opportunity, clean that thing from front to back. Try  to get as much seed out of it as you can. This is an inherited problem, something that came along with the equipment,” Everman said.

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Metabolic weed resistance theme of UT Weed Tour

Ginger Rowsey

Larry Steckel, Extension weed scientist with the University of Tennessee shares information about his latest research during the 2021 Weed Tour.University research points to spreading metabolic weed resistance in Tennessee fields.

Ginger Rowsey | Jun 25, 2021SUGGESTED EVENT

Farm Progress ShowAug 31, 2021 to Sep 02, 2021

The University of Tennessee held its annual Weed Tour on June 16 at the West Tennessee AgResearch and Education Center in Jackson. The overarching theme of the day — metabolic weed resistance is here and spreading.

“We’re clearly seeing metabolic resistance,” said Larry Steckel, UT Extension weed specialist. “It’s different than what we’ve always seen with target site resistance, which is what Roundup or PPO resistance was. With target site resistance, it seems like overnight, the herbicide, even applied at six to ten times the labeled rate quits working on a particular weed. While what we have seen with metabolic driven herbicide resistance typically involved more than one herbicide with the level of resistance two to four times.”https://a9ffbcfe2d577340816712d2d2a5ee6b.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

“We’re seeing it with dicamba and 2,4-D, but we’re also seeing more subtle declines in control with a number of different herbicides, including the Group 15 herbicides like Dual or Warrant,” he adds. “Not that they’re not working, but maybe they were working for 17 days and now they’re only holding 15-16 days.”

Steckel’s take home message for managing metabolic weed resistance: Use the max rate of pre-emergence herbicide for any given soil type. Then, overlay another pre-emergence herbicide. You’ll need two passes of post-emergence herbicides. Be as timely as you can with those post applications.

Visitors to the Weed Tour were able to see dozens of herbicide treatments in the university’s research plots. The tour was led by Steckel, along with Clay Perkins and graduate student Delaney Foster. In addition to plots at the AgResearch Center, Steckel and his crew conduct on-farm research where they are seeing more evidence of metabolic resistance. Even documenting Palmer amaranth escapes from applications of auxin herbicides made at the 4X rate.ADVERTISING

“We’ve got to start thinking about some different ways to manage for it,” he added. “One is to be as timely as possible, which is easier said than done. The other is relying more on pres. Based on my conversations with farmers and retailers, I think we’re using more pre’s this year, and I think that’s helped. They’ve worked for the most part pretty well. But now we’re in the crunch time when all the posts are going out, and I’m expecting some calls from folks who are disappointed in their herbicide performance.”

Combating metabolic weed resistance

Cytochrome P450 is a naturally occurring enzyme that detoxifies foreign chemicals. It’s found in plants and animals, but plants have more genes for the P450 enzyme. Over time growers inadvertently select for weeds with higher numbers of these enzymes in their genetic makeup. These enzymes can then detoxify herbicides applied to the weed.

Researchers often test for metabolic resistance by mixing the herbicide in question with malathion. Malathion, along with all the organophosphate insecticides, are known cytochrome P450 inhibitors. That means they’ll bind up the enzyme that is detoxifying the herbicide.

“When you inhibit those P450’s, the thought is the herbicide will now kill the weed,” Foster said.

Steckel and Foster were hopeful malathion could be a solution. In greenhouse research this past winter, they saw promising results, with malathion improving auxin herbicide control as much as 32% in some treatments. But results in field trials were not as good.

“It worked a little better with 2,4-D than dicamba,” Foster said, “but here we didn’t see a big malathion difference. That doesn’t mean this herbicide resistance isn’t metabolism based. There are hundreds of P450 enzymes and lots of P450 inhibitors. Malathion targets one. We’ll continue evaluating other P450 inhibitors and hopefully figure out what the mechanism of resistance is here.”TAGS: CROPS

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