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Annual meadowgrass

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

 
Mark Ballingall
Senior Weeds Consultant
SAC Research
Biography >>
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Annual meadowgrass is the most common grassweed. It's always there and must be managed. Manage it well and it won't be a problem, but manage it poorly and it will soon get on top of you.

It may not rob yield on the same scale as blackgrass or wild oats, but it can hinder harvest and take advantage of poor crop cover. With the loss of various key autumn herbicides, its control requires a more strategic approach. Growers, especially those in the north, need to take it into account in their autumn spray strategy.

What impact does annual meadowgrass have?

Annual meadowgrass is endemic in most arable fields across the whole of the UK. It will not grow as tall as the cereal crop, so its effect on yield is limited, but it does compete for nitrogen. At harvest, especially in a damp year, it will thrive and retain moisture at the base of the crop. This can slow progress of the combine in a wet harvest.

In the south and east of England, where blackgrass is the dominant grassweed, annual meadowgrass seldom features as a problem weed – it is generally controlled by robust grassweed herbicide strategies. But in the north and Scotland it has become more of an issue.

The rise of minimum tillage has favoured annual meadowgrass and its prevalence is increasing. Previously it was kept in check by a relatively low dose of isoproturon (IPU). But now it requires a more complex herbicide strategy.

How do you identify it?

annual-meadowgrass-in-flower

Preventing annual meadowgrass from flowering is the best way to prevent the seed bank building.

Easily confused with brome as a seedling, annual meadowgrass tends to be a lighter green and germinates much earlier. On closer inspection the grass has boat-shaped leaves, while brome's leaves are sharply pointed. There are no auricles and the ligule is long and smooth.

In the spring it is easy to identify – it is the first to flower with a panicle flower-head and stays low down in the canopy. Rough-stalked meadowgrass looks very similar in the autumn, although this is largely immaterial as its control strategy is very similar. But rough-stalked meadowgrass grows above the crop and has a purple tinge to its stem in late spring and summer.

What is its growth pattern?

You will almost certainly have a huge seed bank of annual meadowgrass in most of your arable fields. One of the most prolific producers of seed, bettered only by blackgrass and brome, one plant will bear about 500 seeds.

Another characteristic is its short growing season. The grass can squeeze two life cycles into a single cropping year – it will shed seeds in March, which can bring on a second flush that is ready to seed by harvest.

Its final key quality is the length of its germination window – the longest of all the grassweeds. Given the right conditions it will germinate all year round.

But it is not in the top tier of competitive grassweeds. It will not compete for light or space, although it will rob the crop of nitrogen.

How do you manage populations?

nh-tractor-ploughing

The plough is a key weapon against annual meadowgrass.

The main way to control annual meadowgrass and keep a lid on its seed bank is to prevent it flowering as much as possible. This is harder than with other grassweeds as it flowers so quickly and so readily.

The plough is your best tool, especially if you can plough down chitted seed and established plants. New plants will grow from misplaced tufts, however, so effective burying with the plough is essential.

Annual meadowgrass will thrive in minimum-tillage situations. Stale seed-beds are generally not practical where there is a short autumn cultivation window. In the north, in particular, the inter-crop interval is generally too short to generate a satisfactory weed seed chit.

Delaying drilling will help as the majority of seeds will have germinated by October. But this must be balanced against lower crop survival over the winter period. A well-tillered crop will prevent meadowgrass from getting established. Low crop competition, as well as the grass' long germination period, make spring crops a poor cultural control option.

What are the chemical control options?

IPU offered very effective control of annual meadowgrass helped by an application timing that was very flexible. Now IPU is no longer available a change of mindset is needed. Timing is now critical to good control, and ideally the weed should be treated pre- or peri-emergence, as it is easiest to control effectively at the one to two-leaf stage or at early tillering. If your main autumn herbicide is delayed, control can be compromised.

At this timing you are looking for a chemical with mainly residual and a little foliage uptake. You will need a relatively clod-free seed-bed and a moist soil for the herbicide to act effectively. The actual choice of active ingredient will be governed largely by what else you are looking to control with the application. Some mixes have better control of broad-leaved weeds than others.

Peri-emergence is also too early for a barley yellow dwarf virus (BYDV) spray, so a second pass may be needed, particularly if an insecticidal seed treatment has not been used.

While there are a number of tools in the armoury for winter wheat, the options for winter barley are quite restricted. Chlorotoluron (CTU) is useful here, although it has a limited effect on large, well-tillered plants.

Note that straight CTU will be withdrawn from sale on 31 August, 2010, and that all stocks must be used over the next 12 months.

You should always aim to control annual meadowgrass in the autumn, ideally with a pre- or peri-emergence treatment. But in winter wheat sulfonylurea + residual herbicides, either as formulated products or in tank mixes, do offer an alternative option that can be effective right up to second node stage in the spring. But these can be an expensive fallback.

It is also worth noting that autumn herbicides will have run out of steam by March or early April while annual meadowgrass will be germinating again. Crops with a poor canopy may therefore need a follow-up treatment if a strong spring flush threatens to take over.

Three Golden Rules

  • Use the plough – it's the most cost-effective tool
  • Delay drilling, but make sure you keep the crop competitive
  • Apply herbicides as early as you can after drilling
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