Knowledge Hub Article

Black-grass - Management Guidance and Best Practice

Control requirements

Aim: 

About 97% control of black-grass is required in a non-inversion tillage system to prevent populations increasing.

The challenge: 

As efficacy of post-emergence herbicides declines as a consequence of resistance, greater reliance on pre-emergence herbicides is needed.

The problem:

It is unlikely that the high levels of control needed from pre-emergence herbicides can be achieved routinely, especially in dry years.

Increased control is needed from pre-emergence herbicides to compensate for the declining performance of post-emergence herbicides.

To achieve 97% control overall:

Control needed from pre-ems.

If control from post-ems. Is only

0%

99%

73%

89%

86%

79%

90%

69%

93%

59%

94%

49%

95%

39%

 < 60% = achievable
60 – 80% = potentially achievable
>80% = unlikely to be achievable routinely

The solution?   

Reliance on herbicides alone for control of black-grass is not a sustainable strategy.  Integrating the use of several non-chemical methods, in combination with herbicides, is the only long-term solution.

Control – herbicides

Pre-sowing – destroying all emerged black-grass plants before sowing a crop is essential.  Use of Roundup ensures a better degree of kill than cultivations alone.

Pre-emergence herbicides, such as flufenacet, pendimethalin, prosulfocarb and tri-allate, can provide a good level of control of black-grass in cereals (50 – 80%) and efficacy is usually only partially reduced by resistance.

Post-emergence herbicides, such as clodinafop, pinoxaden, flupyrsulfuron, mesosulfuron + iodosulfuron, pyroxsulam, propaquizafop, cycloxydim, clethodim, propyzamide and carbetamide, can give good control of susceptible black-grass in a range of crops, but resistance to many of these herbicides is increasing rapidly.

Non-chemical control

 

Typical % control achieved*

Comments

Method

 

 

Ploughing

69%

Rotational ploughing has considerable benefits provided good inversion is achieved

Delayed autumn drilling

31%

Reduces populations and increases control from pre-em herbicides.  Weather dependent

Higher crop seed rates

26%

The higher the better – but lodging issues

More competitive cultivars

22%

Useful but marginal effects

Spring cropping

88%

Very useful – but challenging on heavy soil  and limited herbicides

Fallowing/grass leys

70-80% per year (of seedbank)

Absence of new seeding critical.  More than a single year needed for good effect

Hand roguing

Up to 90%

Labour intensive but very useful at low populations.

Mechanical weeding

50-80%

Feasibility and effectiveness depends on crop

Spraying off patches with glyphosate in early June

Up to 100%

Effective at preventing seed return but crop loss means only feasible on limited areas.

 

These are average control values recorded in a review by Lutman, Moss, Cook & Welham, 2013.  Control will vary considerably in individual fields – better or worse.

Reliance on herbicides alone for control of black-grass is not a sustainable strategy.  Integrating the use of several non-chemical methods should improve overall control and reduce reliance on herbicides.

 

Future issues
  • Resistance to pre-emergence herbicides – how quickly will it increase?
  • Will there be any new herbicides?
  • Availability of herbicides – how many will we lose through EU and individual country’s regulatory decisions?
  • Will resistance to glyphosate develop widely?
  • Cost of non-chemical control measures – can farmers afford these?