Article Published in 'The Khronicles' November 2007

Home Garden.

By Bob Bayes
http://www.qualitygardens.biz/
qualitygardens2004@yahoo.co.uk

When is a worm not a worm? Answer – When it’s a caterpillar.

I was recently asked to investigate a problem lawn. Despite being well watered it was suffering from brown patches, and what was worse, the patches were getting bigger.
As I walked across the lawn a number of small brown moths flew out of the grass away from my feet. This was my first clue.
I took a hosepipe and left it to flood an area of the lawn. A close inspection of the flooded grass revealed a host of wriggling caterpillars. The moths were a type of willow moth (Spodoptera ciliata), which prefers to use short grass as a host plant in which to lay it’s eggs.
The moths of the Spodoptera genus lay eggs in batches of more than a hundred at a time and the resulting caterpillars are known as armyworms and are major pests of many crops around the world.
Lawn armyworms live in the thatch of the lawn and emerge after nightfall to eat the grass back to bare earth. As the army devours an area it marches ever onwards until all the lawn is eaten.
Of course, in the natural environment, grass does not have a very long season in the Cretan climate and so the moths are seasonal too. We, however, expect our lawns to be green the whole year around. This means that the caterpillars never go hungry and so it is possible for the moths to produce many generations over the course of a year.
It is hard enough to grow a decent lawn in such a hostile climate (for grass) without having to wage war on an army!
I have read about nematodes that will destroy the caterpillars, and also of wasps that use the caterpillars as a host for their eggs. But I have no experience of them and I doubt if they are readily available on Crete.
I’m sorry, but if you insist on having a lush green lawn then you will have to use chemicals. A number of suitable insecticides are available here. The one that I have used to some success contains the ingredient ‘chlorpyrifos’ and will keep the lawn clear for up to two months. The brand that is available in the farm shops here, however, is not labelled for use on turf and so I would recommend that you get the help of a professional to carry out any pesticide treatments.
Remember not to allow any animals to graze on a treated lawn and any clippings should not be used for composting. Another consideration is if you have fruit trees growing in the lawn. Obviously you would not want to use any chemicals under these at fruiting time, if at all.

So just what is this ‘thatch’ that I mentioned earlier? The best way that I can describe it is as a layer of both living and dead plant stems that build up between the soil surface and the green grass blades. It is what gives a lawn the springy feel underfoot. It provides an ideal home for many of the lawn pests and diseases and is, on the whole, considered to be detrimental to the well being of the grass if it is deeper than about 1cm.
Thatch is physically removed from a lawn. On a small scale this can be done with a wire tined lawn rake, but a better job is achieved by using an electric or petrol powered machine. This is generally carried out annually on a high quality lawn, whilst the grass is growing well.
Aeration also encourages the breakdown of thatch and should also be carried out at least annually (more often for sports pitches and areas of heavy wear and, therefore, compaction).