Grower’s blackgrass trial reveals host of weed control solutions

Where winter wheat growers are battling heavy blackgrass infestation, a multifaceted approach is needed to rein in bulging populations and restore sustainable gross margins.

In the past three years, Ruth Stanley has seen blackgrass populations escalate on parts of her 400ha farm and it is now having a significant impact on wheat yields.

She needed to find solutions that work on her own farm, fast and with agrochemical giant BASF looking for someone to host blackgrass trials, Miss Stanley jumped at the chance to look at various control options on her own land.

See also: Calculate cost of blackgrass with new tool

A winter wheat-based rotation on heavy soils, with no ploughing and early autumn drilling had resulted on a reliance on herbicides to control grassweeds, which is a familiar tale across arable areas of England.

Actives

  • Atlantis – iodosulfuron + mesosulfuron
  • Auxiliary – clodinafop + prosulfocarb
  • Avadex – tri-allate
  • Crystal – flufenacet + pendimethalin
  • Defy – prosulfocarb
  • Lexus – flupyrsulfuron
  • Stomp Aqua   pendimethalin

“We have had low levels of blackgrass for some time, but it has really exploded in recent seasons and we’ve had target site resistance confirmed to ACCase- and ALS-inhibiting herbicides,” explains Miss Stanley.

Chemical costs

In its first year in 2013-14, BASF’s trial focused on chemistry, looking at 16 pre-emergence and 22 post-emergence treatments on Miss Stanley’s worst field.

The most effective programme against a background population of 494 heads/sq m was a huge pre-emergence stack – Crystal + diflufenican + Lexus + Defy – followed by Atlantis + Stomp Aqua + Auxiliary post-emergence.

Although the programme achieved 95% control, it still left too much blackgrass behind, with the remaining head count about 25 heads/sq m and seed return expected to be in the region of 2,500 seeds/sq m.

Miss Stanley says the programme cost about £130/ha and with wheat at about £110/t; it highlighted the need to find a more integrated, cost effective approach to solving the problem.

“That just isn’t economic and the solution isn’t out of a can anymore, controlling blackgrass is going to be hard – and stressful. Taking that on board, this year the trial has looked at both cultural and chemical control,” says Miss Stanley.

Sprayed off blackgrass

© Tim Scrivener

The effect of cultivation and establishment method, drilling date, cover cropping and some differing herbicide treatments on blackgrass numbers were assessed.

Plough-based and min-till cultivation systems were used alongside a direct drill and for consistency of drilling, the same Weaving disc drill was used across all plots.

BASF open day

Comments in this article were taken from BASF’s open day at the 400ha New Farm at Harby, near Melton Mowbray. Ruth Stanley farms in partnership with her father on top of her role as the company’s East Midlands agronomy manager.

KWS Gator winter wheat was drilled on 28 October and 9 December, with the variety chosen for its drill-date flexibility.

Spring wheat variety Willow was established on 14 March, with a proportion following an oil radish cover crop.

Challenging soils

A dry autumn meant the ground was too hard to plough until October and planned stale seed-beds were not possible in the early drilled trial, with just one glyphosate application possible before drilling.

A wet period meant the later established plots had to be drilled on a frost, highlighting the challenge that heavy land farmers have, but it did allow an extra glyphosate application.

“If there is one message from the trial, it’s that later drilling and getting as many stale seed-beds as possible is crucial,” says Miss Stanley.

Just one extra application of glyphosate pre-drilling resulted in a much lower blackgrass population, but in the spring wheat plots where three stale seed-beds were possible, numbers were less again.

“We have seen that if you aren’t going to get your late-drilled wheat into good conditions, you are better off waiting until the spring.”
Ruth Stanley, BASF

“We have seen that if you aren’t going to get your late-drilled wheat into good conditions, you are better off waiting until the spring.”

Despite the pre-emergence herbicides used in the trial struggling to give comprehensive control, there was one consistent theme through all the plots.

Where granular herbicide Avadex was added to the stack ahead of a peri-emergence application of Crystal + diflufenican, it provided consistently better control.

“Avadex is making a big difference and it’s something that we can do in one pass, as we have an applicator on our drill. Rates of products need to be kept up too – don’t skimp,” adds Miss Stanley.

Cover crops

The trial has also taught Miss Stanley some lessons on implementing cover crops, something that many growers are looking to do now for soil health benefits and the possibility of aiding with blackgrass control.

“I have certainly learned how not to grow cover crops. We planted the oil radish too late and in wet conditions, so next time we’ll try and get it established much earlier.

“The one positive is that it did take the moisture out of the ground, which is crucial on our heavy land if we are going to establish cereal crops in the spring,” she says.

Bravery pays

George Cook of business consultants Andersons carried out a cost analysis of all the plots, estimating gross margin with or without losses from the remaining blackgrass numbers (see table).

All the crops are predicted to make a loss, although some more substantial than others and Mr Cook says it’s a situation familiar to many farms with a high blackgrass burden.

He advises growers to be brave enough to stop seed return, even if it means losing £400/ha in costs, as that loss could multiply many times over the next three years.

“The challenge going forward is adapting to a lower output system which includes spring crops and/or fallows, as it takes time to adjust your cost base – particularly if you are geared up for high autumn workloads with high horsepower machinery.

“Even if grain prices return to a more economic level, grassweeds aren’t going away, so growers need to find a strategy that allows them maintain profit from lower crop sales,” he explains.

Cultivations and sowing date trial

Plot 1: Winter wheat drilled 28 October 2014
 

Plough

X-press

Direct drill

Blackgrass plants/sq m
(May 2015)

19

33

50

Yield loss (£/ha)

34.50

69.00

109.25

Margin (£/ha)

754.52

713.52

671.02

Margin (£/ha)
(no blackgrass loss)

824

824

824

Difference

-69.48

-110.48

-152.98

 

Plot 2: Winter wheat drilled 9 December 2014

 

Plough

X-press

Direct drill

Blackgrass plants/sq m
(May 2015)

3

5

36

Yield loss (£/ha)

5.75

11.5

80.50

Margin (£/ha)

803.36

819.86

719.86

Margin (£/ha)
(no blackgrass loss)

824

824

824

Difference

-20.64

-4.14

-104.14

 

Plot 3: Spring wheat drilled 14 March 2015
 

Plough

X-press

Direct drill

Blackgrass plants/sq m
(May 2015)

0

60

101

Yield loss (£/ha)

122.50

187.50

Margin (£/ha)

658.78

441.78

387.58

Margin (£/ha)
(no blackgrass loss)

660

660

660

Difference

-1.22

-218.22

-272.42

 

Plot 4: Overwinter cover crop followed by spring wheat
 

Plough

X-press

Direct drill

Blackgrass plants/sq m
(May 2015)

7

6

77

Yield loss (£/ha)

37.50

50.00

156.25

Margin (£/ha)

583.78

624.58

450.08

Margin (£/ha)
(no blackgrass loss)

660

660

660

Difference

-76.22

-35.42

-209.92

Assumed winter wheat yield 9.5t/ha, spring wheat yield 7.0t/ha, winter wheat price £115/t and spring wheat £125/t.

Industry view – what can help beat blackgrass?

John Miles, KWS

John Miles“Variety choice plays a minimal part, but getting the right one at the right time is important.

“If you are going to a later sowing, you need a vigorous variety with speed of movement and the ability to compensate from gappy establishment from poor seed-beds.”

Sarah Cook, Adas

Sarah Cook“We offer blackgrass herbicide resistance testing and would urge growers to have their populations tested.

“Once resistance is there, it is not going away and you’ll need to get rid of the seed and confirmation by testing will focus your mind on doing that by cultural means.”

Paul Brown, Kings Seeds

Paul Brown“Cover crops can certainly have a role to play in reducing blackgrass and in our trials we have seen oil radish reduce grassweed numbers to almost nothing from both a smothering effect and what looks like an allopathic effect.

“The key to cover crop success is to get them away early to harvest as much sunshine as possible.”

Neil Fuller, independent soil and crop nutrition specialist

Neil Fuller“The more you can improve the structure and drainage of a cold, wet soil to something warmer and more aerobic, the less the blackgrass will like it.

“I also think we can use the expected dormancy of blackgrass seed to make management decisions from year to year and where dormancy is high, go for a cover crop, spring crop or fallow to reduce the numbers germinating in the crop.”

Growers’ view

Keith Challen, Vale of Belvoir, Leicestershire.

Keith Challen“The take home message from Ruth’s trials is where parts of last year’s trial were sprayed off with glyphosate (due to high blackgrass numbers), you’re farming again.

“A one-year hit has already paid off and it’s something that we’re already doing at home.”

George Renner, Rutland Water, Rutland

George Renner“Everywhere you go, blackgrass seems to be getting worse and we have low levels on our land, despite lighter soils and spring crops in the rotation.

“From the trials, you can see that you have to prevent seed return at all costs and we are getting out with the knapsack and spraying off patches where we can.”

 

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