What Is It?
As the name suggests, Black Layer is sometimes a continuous layer usually just below the turf which is distinctly black. The chemical definition is a deposit of metal sulphides caused by the activity of anaerobic bacteria.
Have I Got It?
The easiest way to find out if you have Black Layer is to take out a sample of the turf with a knife or core sampling tool. You will see either black streaks or a continuous band which will smell of bad eggs, this is hydrogen sulphide gas. The effect on the surface of the turf will be yellowing of the leaf and thinning of the sward.
One of the major contributory factors of Black Layer is a waterlogged soil profile. When this occurs aerobic bacteria, which are beneficial, cannot survive. The anaerobic bacteria dominate the rootzone as there is little or no oxygen. This group of bacteria respire hydrogen sulphide as aerobic bacteria respire carbon dioxide. The hydrogen sulphide gas bonds with metal ions such as iron forming the band we call Black Layer .
How Do I Control It?
Because the major factor in Black Layer is poor percolation of water, aeration is crucial. Firstly hollow core to remove a percentage of organic matter from the surface, following by deep slitting to maximum possible depth. If there is an underlying drainage problem this should be addressed. As a remedial measure to help the turf recover a product containing activated charcoal can be applied. Use this after hollow coring and it will absorb the hydrogen sulphide gas which is toxic to the grass plants. Introducing oxygen to the rootzone will kill anaerobic bacteria.
Whilst Black Layer persists it is advisable to use fertilizer which contains little or no sulphur. Therefore ask the Rigby Taylor technical staff about the ingredients used in the various formulations.
How Do I Try To Prevent Re-Occurrence?
Prevention is similar to control. Frequent aeration is a key to keeping black layer at bay. Try to control the build up of organic matter which happens naturally with dieback of grass leaves and roots. This should be done mechanically using a mower fitted with a verticutting reel, or a special scarifier. If a scarifying machine is used ensure when operated in the playing season the set is not too deep, otherwise the surface may be affected. After the season vigorous scarification is perfectly acceptable.