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26 September 2017

Annual Meadow Grass (Poa Annua)

Annual meadow grass (also commonly known by its Latin name of Poa annua) is sometimes found in rolls of cultivated turf.
 
OCCURENCE
 
Annual meadow grass is one of the most widespread grasses in the world. It is found from Tierra del Fuego to the Arctic Circle and from sea level to the tops of mountains. It will grow in the cracks between paving stones and in roof gutters and is the dominant grass in most UK golf greens.
 
Most established lawns contain some annual meadow grass, but it usually well blends in well with the other grasses. It is a common weed of arable land and thus is often found in cultivated turf.  Although it is called annual meadow grass, some forms of it are short-lived perennials and will therefore persist from year to year.
 
Annual meadow grass has no perennial underground stems or roots so if the shoots are completely removed it cannot re-grow from under the ground.
 
QUALITY CONTROL
 
Turfgrowers around the world do their best to control annual meadow grass in their production fields, and TGA members take quality control very seriously. It is very difficult to selectively kill one grass species growing in a mixture with other types of grass. Until quite recently, it was possible for turfgrowers to use chemical control to eliminate annual meadow grass from turf.  Unfortunately, however, the main herbicide that was used to do this is no longer available and cultural methods (less reliable) have to be used.
 
Before lifting the turf the grower will assess the amount of annual meadow grass present.  If it is deemed to be within acceptable limits the turf will be passed as fit for sale.  Since the withdrawal of effective herbicides, the amount of annual meadow grass deemed acceptable in turf has increased.
 
HOW TO MINIMISE IT IN A LAWN
 
Annual meadow grass in a lawn can be made less noticeable by good management. It often has a pale green colour and applying a fertiliser will help improve its colour so that it blends in with the rest of the lawn.
 
Because this grass spreads by seed, it is best to remove grass clippings when mowing. Brushing the turf to raise the seedheads before mowing will help to remove them. It should not be necessary to use a powered scarifier on a recently laid lawn but hand raking and brushing can help.
 
Complaints about excessive annual meadow grass are sometimes received from customers after the turf has been laid.  This is often due to the turf being allowed to become too tall before the first mowing, allowing the stems of the annual meadow grass to splay out.
 
Mowing of the new lawn should commence as soon as the turf is well anchored to the soil underneath. Lift a corner of a roll to see how well it has rooted and then begin mowing - aiming to get the mowing height of the turf back to what it was when it was delivered as soon as possible after laying. The turf should not be allowed to get very long and, ideally, it should have no more than about a third of its length removed at each mowing.
 
Infrequent mowing can also have the effect of making the isolated annual meadow grass plants in a new lawn appear more widespread than they actually are, because the individual stems of the grass are able to radiate out sideways from their base.
 
To remove clumps of annual meadow grass in a relatively small area it is possible to weed it out by hand by cutting through the base of the plant just below the surface of the soil using a sharp knife. Any bare ground revealed should then be lightly scratched and a good quality seed mix to match the turf should be sown to repair the patch.
 
Alternatively, carefully treat each annual meadow grass plant in the lawn using Roundup Gel (from a garden centre), following which it will gradually turn yellow and die. Bear in mind that this is a total weedkiller so will kill every plant it touches so do it carefully.
 
Produced for the TGA by independent agronomist Robert Laycock, member of RIPTA.