Weeds

You might love them, as they are wild flowers, hate them, as they can make a lawn (or sports surface) look very unsightly if present in large numbers, or just tolerate them. Weeds, what are they though?

A weed? A Dandelion in flower

A weed? A Dandelion in flower

A definition

An undesirable plant. Sometimes the wording ‘growing in an unwanted place’ is added to a definition, but this doesn’t really add any extra value to the meaning, because it is still undesirable at the end of the day. Weeds can be categorised as Broad-Leaved Weeds and Small-Leaved Weeds.

Broad-Leaved Weeds             A general term that might refer to two possibilities: Firstly, Plants with leaves that are not grass like, which is basically most types of traditionally accepted meaning for a weed that isn’t a grass. Or secondly, Weeds that are relatively large, such as Buttercups, Cats-Ear, Daisies, Dandelions, Plantains and Thistles. This would be in contrast to Small-Leaved Weeds which would include Clovers, Parsley Piert, Pearlwort, and the like.

Problems with weeds

Weeds can be undesirable in a number of ways, including:

  • Having a negative impact on the look of the turf, i.e. it looks unsightly especially when weeds are in flower;
  • They compete for a range of resources needed by turfgrasses, including water, nutrients, light, available ground cover and rootzone volume;
  • Smother and outcompete desirable grasses;
  • They can harbour small insect pests;
  • Sports surfaces can become hazardous where a large content of weeds create a slippery surface when moist conditions are present, and players can’t get adequate grip with their footwear;
  • Weeds have different growth patterns to grasses and can create an uneven playing surface which would be especially noticeable for shorter surfaces such as golf, bowls, tennis and cricket;
  • When weeds die off, or are removed, they will typically leave a thin or bare area prior to grass being able to become re-established.
Dead weed

Photograph showing the remains of a weed that has been killed by a chemical; this area will now need to be recolonised by turfgrass

Making the lawn or sports surface as suitable as possible for the desired turfgrass species will help to ensure a more competitive turfgrass is produced: This can then hopefully outcompete any potential weeds.

This will rarely happen in practice, however, conditions can be produced and good maintenance practices applied which will make the situation more favourable to the turfgrass plant.

Good cultural practices, such as ensuring

  • the correct fertiliser is applied (which means having a suitable Nitrogen content – not too high or low; other nutrients are included only if required; the soil reaction created by the fertiliser is appropriate for the sward; it is applied at the correct time of year; …);
  • any grass seed which is sown consists of appropriate species, is sown at a suitable rate, at a suitable time for rapid germination and establishment and is properly maintained after sowing and germination has occurred;
  • top-dressings which are applied are done at a suitable rate so as not to smother a sward; have a suitable particle size analysis; have suitable pH;
  • maintenance activities are carried out to encourage a dense grass sward, such as having a correct height of cut; not removing too much leaf growth per cut; not over or under watering; scarifying at the correct time of year for the intensity / depth of scarification; aerating under correct soil conditions so as not to produce a smeared and compacted soil.

Good physical practices, which may also implement good cultural requirements, such as

  • Mowing with a well-set mower, producing a clean cut; not shaving a sward; using a suitable mower for the desired standard of surface;
  • Scarifying at the correct speed and intensity for ground conditions;
  • Aerating to a suitable depth and using suitable tines for the conditions; varying the aeration techniques – compressed air, drilling, physical tining and varying tine depth;
  • Decompacting the soil using deep tines, linear tining, deep drilling, or deep compressed-air injected technique;
  • Irrigating routinely but effectively when required, occasional and to depth in many cases is more appropriate than a little and frequently to a shallow depth (the latter is more appropriate for newly germinated seed, initially anyhow);
  • Drag-brushing disperse earthworm casts, removing dew, or prior to mowing or in between mowing days;
  • Applying fertiliser evenly using a correctly calibrated spreader, and for maintaining a dense sward throughout the year;
  • Top-dressing to maintain an even surface, without divots or similar in which weeds can more easily colonise;
  • Spreading wear over an area, redirecting ‘traffic routes’, so that wear and compaction is spread as evenly as possible;
  • Hand weed on a regular basis; a few weeds each time an activity is carried out, or when the surface is inspected can make a significant contribution to overall weed control.

Only after a well-planned and executed maintenance programme has been implemented should selective herbicides (weed killers) then be considered. For small garden lawns there shouldn’t really be any need to spray a weed-killer as physical and cultural controls should be practiced properly, with hand weeding being a key activity. Spraying toxic substances within a confined space such as a garden is not conducive to improving the situation for small animals and insects, so don’t do it and burn off some calories instead.

Clearly if a large area is covered in weeds then the cause of this infestation needs to be investigated as part of an Integrated Turf Management programme as spraying will typically provide a short-term outcome; getting to the root cause of a high weed population will be key, otherwise this will just reoccur in the future.

A common cause of a high weed content is that of either an inadequate maintenance programme with resources just not meeting the needs of the surface, or some elements of ineffectiveness in working practices, often due to understaffing and having to rush available tasks, but also due to a misunderstanding of how to manage a turf surface with all the different interconnecting maintenance activities and management issues which can arise.

Chris Gray, 16th February 2019