Non-chemcial strategies for blackgrass control in wheat

The best non-chemical strategy to control blackgrass is to delay drilling until at least mid-October, according to Dick Neale, technical manager for Hutchisons.

“There is little point in growers agonising over which variety they should grow if they are going to drill mid-September in a heavy blackgrass situation,” he says.

“The heavy burden of blackgrass in that early drilling slot would just overwhelm any variety you drill, negating any differences in how individual varieties compete with blackgrass.

“You should only begin to start looking at the finer points of which varieties to sow and what seed rates to choose in a late-drilling situation.”

However, wheat growers who have a heavy blackgrass burden should drill at a minimum seed rate of 450 seeds/sq m, he says.

Mr Neale is making his recommendations based on a new Hutchisons project looking into non-chemical strategies for blackgrass control.

For the trials, large unreplicated demonstration plots – both treated and untreated – of 12 mainstream wheat varieties were drilled in late October.

The interactions between variety and seed rate – either 300 or 500 seeds/sq m – were observed.

“Oakley and Conqueror gave the best control against blackgrass,” says Mr Neale, commenting on the results.

“If you have Oakley in a dry seed-bed, the variety alone will give you 90% control of blackgrass.

“JB Diego and Duxford were next with around 70% control, while Shire did a good job, but only at higher seed rates.”

Panorama and Invicta were also much more effective against blackgrass when sown at high seed rates, he adds.

However, JB Diego and Duxford did not respond much differently in their control of blackgrass at high seed rates, says Mr Neale.

“Both varieties gave good competition to low seed rates. These are the type of varieties you could grow in early October,” he says.

“Then you could save your high seed rates for the later drilled fields, for example, of Oakley, Shire, Panorama or Invicta.”

By contrast, Cordiale and Grafton, which are both suitable for early sowing, offered poor control of blackgrass.

Grafton, an extremely short, stiff variety, offers no competition and suffers in heavy blackgrass populations, says Mr Neale.

“Grafton is being marketed as an extremely good early drilled variety. But if you have bad blackgrass and are trying to control it, you wouldn’t be considering drilling in early September,” he says.

“I would avoid drilling Grafton in a heavy blackgrass situation – it doesn’t offer good competition.”

Cordiale grows well alongside blackgrass, but does not offer much competition, he adds.

“If you grow Cordiale you would expect to see a lot of blackgrass, although the crop does not seem to suffer that much.”

Whereas some varieties, such as Oakley, appear to detect the presence of blackgrass much more strongly and work hard to fight it, says Mr Neale.

“This suggests that some sort of chemical reaction is being sent out at the rooting stage between the variety and the blackgrass.”

Competitive varieties: Blackgrass control

  • Best control – Oakley, Conqueror
  • Good control – JB Diego, Duxford, Shire, Panorama, Invicta
  • Poor control – Cordiale, Grafton

Researching the alternatives

Research into the effects of different row spacing and seed rates in winter wheat is being carried out in a bid to find alternative non-chemical methods to tackle blackgrass.

For the project, led by NIAB TAG, the cultivars Solstice (a shy tillerer) and Robigus (an active tillerer) were planted last autumn at three UK sites.

The varieties were planted at different seed rates – 100, 200 and 300 plants/sq m – in row widths of 12cm, 24cm and 36cm.

“We want to establish how much of a yield penalty you get by growing wheat in a wide row and quantify it,” says Ben Freer, project co-ordinator and head of technical services at NIAB TAG.

Increasing row widths and upping the seed rate within each row could “smother” weeds within the sowing band, he adds.

Then, by applying glyphosate through a sprayer with cowls fitted over the nozzles, it would be possible to spray off the grass weeds once they have emerged.

“While this may seem a bit extreme, we need to be ready to bring alternative methods into play and the work needs doing now,” he says.