Worms and worm cast problems on lawns

Worms are in many cases the gardeners friend as they provide a valuable contribution to the health of the lawn. Worms keep the soil aerated and breakdown the organic matter helping control the thatch layer. In fact a large population of worms points to a healthy soil.

However, despite these benefits worms are often seen as a problem on lawns and other areas of turf as they produce casts. This is especially true if the root zone or soil has a high clay content.  It this is the case then problems caused by worm casting may actually outweigh the benefits.

On a clay soil the worm casts tend to smear on the surface and can actually muddy conditions On lawns with a lighter root zone worm casting will be less of a problem as the worm casts are more easily dispersed.

There are many different species of worms, of which only 3 species actually produce casts.

Worms are a major problem on lawns during mild spells in the autumn and winter months when the soil becomes wetter thus encouraging worm activity close to the surface of the lawn. During colder, frosty weather the worms head deeper into the soil and are less problematic.

Problems caused by worms and wormcasting include:

• Wormcasts create muddy conditions.
  
• Encourages moles (worms are the food source of moles).
  
• Weed and weed grass invasion ( wormcasts create an ideal seedbed for weeds).
  
• If casting is very severe the levels of the lawn may be affected.
  

What causes worms in lawns

As with most problems in lawn care, worms favour particular conditions to be present within the soil. These soil conditions include:

• Wet soil and mild temperatures - Worm are predominantly a nuisance on lawns during wet mild spells of weather during the autumn and winter months. These conditions bring worm activity closer to the surface of the lawn where casts are deposited.
  
• Soil type - Although worms may be present in all types of soil conditions, they are more of a problem in soils with a high clay and high thatch (organic matter) content.
  
• The correct soil pH. Worms prefer soils with a high pH.
  
• High organic matter content. A soil with a high percentage of organic matter (thatch) will have a greater population of worms as this is there food source.
  

Preventing worms and wormcasts on the lawn

Without the use of chemicals (used by turf care professionals) to prevent worm and wormcasts problems on lawns, most amateur lawn enthusiasts are limited to cultural control methods. However it is important to understand that even with a good cultural worm control program you may still be met with limited success.
These cultural methods include:

• Reducing the organic matter content - As worms feed on organic matter it makes sense to reduce their food supply. operations such as scarifying and hollowtining will help reduce the organic matter (thatch) content. Boxing off clippings when mowing the lawn will prevent organic matter build up. Remove any leaves from the surface of the lawn during periods of leaf fall in the autumn months.
  
• Reduce the pH of the soil - Worms favour a soil with a high pH therefore only apply materials (fertiliser, top dressings etc) with a low pH. Over a period of time this will gradually reduce the pH and hopefully reduce the worm population in the lawn.
  

Chemical control of worms in the lawn

As mentioned earlier, even with good cultural practices to remove worms success can be limited and you may be left disappointed with the results. In the sports turf industry chemicals are used to control worms. However products such a chlordane which were used many years ago with great success are no longer available.


The only chemical currently available for worm control is a product called carbendazim which is widely used in the turf care industry. Carbendazim is actually a fungicide used to control fusarium and other lawn and turf diseases, however carbendazim also has worm suppressant properties. N. B. carbendazim (unlike previously banned chemicals) does not kill the worms, it acts more of an irritant and the worms simply go deeper into the soil.

Although this product is not available for amateur gardeners, professional lawn care companies of which there are many, can apply this chemical. Therefore if you feel that your worm problem warrants chemical treatment you may want to enlist the services of one of these lawn care specialist. However like many chemicals used in lawn care, they should only be used as a last resort.

Should I control worms

In most cases worms are best being left alone as they are good for the soil. The majority of casting will take place during the winter months when there will be little activity on the lawn anyway. If there are is any worm casting they can be brushed off the lawn with a besom (a brush that looks like a witches broom) or similar tool or implement during drier periods in the winter.

However, other gardeners may spend a lot of time and take great pride in their lawn and due to soil conditions worms may be causing the lawn to deteriorate somewhat. In this case someone may feel that worm control is justified.