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Brome grasses

Course: Weed control | Last Updates: 10th October 2015

 
Ben Freer
Head of Technical Services and Regional Agronomist
NIAB TAG
Biography >>
FADS2NRoSO2BASIS2

The adoption of shallower, non-inversion tillage and earlier drilling has led to a big increase on UK farms.

Worldwide there are 165 species of brome grasses, but in the UK there are four main species that interfere with yield and quality of arable crops.

Their identification as a group (compared to other grassweeds on the farm) is fairly straight forward but differentiation between the species is more difficult. Clues to the exact species centres on the hairiness of the leaves and the shape of the ligule. When small and tillering the leaves tend to be twisted, they are usually a paler green than the crop. When the heads emerge identification is more straightforward, and while at this point the ease of identification indicates you have failed to control them, management of seed return and tactics for their control in the following season mean this is, in fact, the easiest method.

Identifying which species you have is important as it will determine the most appropriate control measures.

They are divided into two groups;

1. The Anisantha family – barren brome and great brome (Anisantha sterilis and A diandra), and the Serrafalcus family

2. Soft and Meadow brome (Bromus hordeaceus ssp hordeaceus and B commutatus, also rye brome, (B secalinus).

Barren, or sterile, brome (Anisantha sterilis)

Golden rules

  • Identify the species
  • Spot the problem early – harvesting and cultivations spread the seed
  • Consider spraying a sterile strip around crop edges
  • Consider spot spraying patches of crop/weed with glyphosate
  • According to the specie cultivate or leave, on the surface after harvest
  • For all brome species, a herbicide programme will deliver the best results
  • For barren and soft brome always aim to complete the herbicide programme in the autumn
  • Avoid applications in dry / cold conditions when weed growth is slow

This is the most common species in the UK; it can reach 100cm in height. The plant is usually a light green in colour, but turns purple after flowering. The leaves are flat, soft and hairy with the youngest leaves rolling. The flower head occurs on a long stalk and tends to droop. The flowers are grouped into spikelets. Seeds are relatively large, up to a 1cm in length. It is a common weed on farms and will grow on any soil type, but thrives on light, sandy and well-drained land. It can become a serious weed in field margins. Barren brome occurs throughout the UK. It germinates quickly in the absence of light. Autumn is the main period for emergence but if dormancy is enforced by drought or low temperature, seed may persist through to the following spring.

Great brome (Anisantha diandra)

A bit shorter than barren brome at 90cm, great brome leaves are rough, hairy, dull and often have visible purple stripes along the leaf veins. It is similar to barren brome when flowering but has a larger head. The leaf sheath is tubular, the ligule is prominent and membranous, and the stems are hairy. The inflorescence is a loose, nodding panicle with long stalked spikelets. Autumn is the main period for emergence, but if dormancy is enforced by drought or low temperature, seed may persist through to the following spring.

Meadow brome (Bromus commutatus)

An annual or biannual grass, it grows to a height of 120cm. It is very loosely tufted and sometimes singly. Mature plants have dense soft hairs on the sheaths. Leaves are greyish-green in colour. Panicles are loose, open and eventually drooping to one side. Compact flower spikelets are hairless and occur in early summer. It is widespread across the UK, most frequently found on moist lowland soils typically in continuous autumn sown cereals or continuously autumn sown crops. Seed is larger than barren brome. It requires light and warmth to germinate. Most seeds germinate in the autumn.

Soft brome (Bromus mollis)

An annual grass often found in cultivated areas where the soil is open and frequently disturbed. It grows to a height of 100cm. Mature plants have dense soft hairs on the sheaths. Leaves are greyish-green in colour. Compact flower spikelets occur in early summer. Most seeds germinate in the autumn.

Growth pattern

Barren brome (A sterilis), the most common species, often infests cropped headlands. Incidence varies considerably between years according to autumn soil moisture conditions. Dry soils after harvest can result in it emerging after the crop is sown. Barren brome flowers from May to July; a large mature plant may have up to 10 fertile tillers. Flower heads have 10-12 spikelets each containing four to 10 seeds. On average, more than 200 seeds are produced per plant and a high proportion is viable. Seeds start to become viable three to seven days after flowering.

Meadow brome (B commutatus) and soft brome (B hordeaceus ssp hordeaceus) frequently infest continuous winter wheat crops or continuous autumn sown crops. Plants can emerge in the late autumn/early winter.

The vast majority of seeds of barren, meadow and soft brome, when buried in the autumn, will have died or emerged by the spring.

Impact on the farm

Yield reduction from plant competition is the greatest impact but high populations will also cause lodging (and subsequent yield loss). Unshed seed will contaminate the combine and baled straw and spread the problem across the farm/on to other farms.

 

How to manage populations

Cultural control strategies

Very few seeds of all above species survive more than a year in the soil. But seed must be effectively buried to 15cm or more in consolidated soil by ploughing. It is best to leave soft and meadow brome seed on the soil surface for a month after harvest, before ploughing.

Some seed loses its dormancy and survival in soil is reduced and the seed may emerge more synchronously easing herbicide timing decisions. Spray off with glyphosate prior to drilling.

Seriously consider ploughing for barren (sterile) and great brome. Most barren brome seeds germinate more rapidly in the dark than in the light. In the absence of complete straw cover, shallow cultivation immediately after harvest stimulates barren brome seed to germinate.

But, the stale seed-bed technique only significantly helps to reduce barren brome populations in a successive autumn-sown crop if the soil is sufficiently moist both after harvest and subsequent shallow cultivations and sowing of the succeeding autumn-sown crop is delayed.

It is best to leave soft and meadow brome seed on the soil surface for a month after harvest, before ploughing. Some seed loses its dormancy and survival in soil is reduced.

Because of this, and because control of these bromes with herbicides is relatively poor, ploughing is recommended to control soft and meadow brome prior to drilling winter cereals.

Chemical control strategies

Herbicides should be timed to the peak emergence of respective grassweeds.

For barren (sterile) and/or great brome, optimum control should start with a pre-emergence application based on 240g/ha flufenacet (such as Liberator) or with pendimethalin (such as Crystal). Avadex Excel (triallate) is an alternative for those wanting to take a break from flufenacet use; or it can be used as an additional stacked pre-emergence treatment for those with severe infestations, such as on headlands.

The pre-emergence must be followed up with a suitable ALS-inhibitor in the autumn at the one-to three-leaf stage when growing conditions are good such as Atlantis (iodosulfuron + mesosulfuron), Broadway Star (florasulam + pyroxsulam), Broadway Sunrise (pendimethalin + pyroxsulam), or Unite (flupyrsulfuron-methyl + pyroxsulam).

For meadow and soft (and rye) bromes; timing of the post emergence treatment is more flexible. Optimum control should start with a pre-emergence application based on 240g/ha flufenacet or pendimethalin. Apply post-emergence herbicides in autumn or spring up to mid-tillering of the brome. Atlantis, Broadway Star, Broadway Sunrise, Pacifica or Unite are all active.

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