Herbicide resistant poppies mean trouble for growers

More spring cropping this season could create the perfect conditions for increasing herbicide resistance in poppies.Luke Casswell  visited a trial site in Nottinghamshire to find out what can be done to prevent the growing problem.

Growers are being warned to prevent another “blackgrass disaster” happening with poppies by ensuring they use different types of herbicides and carefully select their spring cropping land.

Spring crops have relied heavily on the ALS-inhibiting sulfonylurea herbicides, such as metsulfuron, to control broadleaved weeds, which has heaped selection pressure on poppy populations and led to reduced control in some areas of the country.

See also: Resistance concerns also mount in Mayweed populations

The situation could rapidly deteriorate this season if growers don’t begin managing their broad-leaved weeds now, according to BASF agronomist Ruth Stanley, who says more spring cropping is expected to follow new CAP greening rules and a burgeoning blackgrass problem.

“It will be the next blackgrass if we are not careful. We have to prevent the resistance getting to the same level because this could be very damaging to arable farmers,” she says.

Resistance to the widely used ALS-inhibiting sulfonylureas has already been found in three of the key broad-leaved weeds, namely chickweed, mayweeds and poppies.

The target site resistance seen in poppies blocks the site of activity of sulfonylureas leading to poor control and is becoming more prevalent particularly in the eastern areas of the UK.

Trial work

Work has been carried out on a suspected poppy resistance population near Newark, Nottinghamshire, by Miss Stanley and Farmacy agronomist Charles Wright. The trials have underlined the importance of applying residual herbicides in spring crops and careful rotation planning.

Top tips on controlling broad-leaved weeds

  • Only use sulfonylureas with an appropriate tank-mix partner and at robust rates
  • Pre-emergence treatments vital in spring crops
  • Monitor high poppy infestations carefully
  • Spray while the weeds are still small
  • Plan rotation carefully

Traditionally, growers have opted solely for an ALS herbicide post-emergence in spring crops but this needs to change, she explains.

“Broad-leaved weed resistance can arise in fields where crop rotations are limited, where weed populations are high and where ALS herbicides have been used repeatedly or alone,” Miss Stanley adds.

The trial site that is currently a spring wheat crop has had repeated use of sulfonylureas over a number of years and has seen increasing numbers of poppies, prompting concerns of resistance.

“This is a red-flag situation that will need action. There will be many growers with these sorts of fields that need to think about what crop is going in next and what their weed management will be,” she explains.

They both trialled a number of options on the farm to determine the level of broad-leaved weed control and found that when a residual herbicide is brought in, control improves markedly.

The trials looked at the pendimethalin-based Stomp Aqua at a rate 2.9l/ha and Picona, which also includes picolinafen, at 3.0l/ha, with both giving good control of the broad-leaved weeds.

Miss Stanley advises using the BASF’s product Picona because it delivers long-lasting residual control as well as contact activity for emerged weeds.

Some commonly used sulfonylurea herbicides

  • Ally Max SX – metsulfuron-methyl
  • Harmony M SX – metsulfuron-methyl + thifensulfuron-methyl
  • Jubilee SX – metsulfuron-methyl

“It is also an ideal mixing partner for products with a weakness on fumitory, poppy, cranesbill and shepherd’s purse,” she says.

Mr Wright adds hormone chemistry such as MCPA and CMPP will provide a useful alternative post-emergence, despite being unpopular with some growers due to their application cut off date.

While spring crops present the opportunity of a lower input crop, that help to spread the workload, he warns a good spray programme will still be needed to prevent problems further down the line.

“One of the problems that growers may have experienced in recent years is lack of control through reduced rates. If you are using SU chemistry then go on with a robust rate to reduce the chance of resistance,” he says.

Mr Wright adds growers should not be afraid of investing into the typically low-input crop with a view to build yield, improve harvestability of crops and reduce the weed seed bank.

Spring cropping land

Growers will also need to assess their rotations this autumn and plan carefully where they are leaving land for spring cropping, according to Mr Wright.

“Switching to spring cropping can open up the risk of broadleaved weed resistance with areas that grow continuous spring crops providing the biggest risk,” he says.

It will be the next blackgrass if we are not careful. We have to prevent the resistance getting to the same level
Ruth Stanley, BASF

Mr Wright advises growers to select a cereal spring crop in order to offer competition against weeds in areas where problems are particularly bad, and to give the growers a wider range of actives to tackle broad-leaved weed populations.

Suspected cases of resistance where poor control has been achieved in previous seasons should be investigated with resistance testing being the best way of finding a solution to this potentially growing problem.

He points out that tell-tale signs of resistance will include patches of weeds in fields that return every year, dead and alive weeds in the same patch and symptomless weeds in a sprayed field.

Future

As herbicides come under more pressure from the water framework directive, the importance of looking after the full armoury of products with best practice will be key in the future.

“We’re at a stage where we still have a number of actives available so we need to look after them and not put too much pressure on certain chemistry,” Mr Wright adds.