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Earthworms, pest or friend ?
by Jim Arthur

 

It is well over a century that Tennyson said that "in the Spring a young man's fancy, lightly turns to thoughts of love". That may be so but in my experience greenkeeper's thoughts in Spring are more geared to killing things which have the potential to upset their cherished turf. Chief among these is the earthworm, so beloved by Charles Darwin and farmers.

I still meet some of the latter masquerading as Chairmen of their Club's Green Committee, who despite all the evidence cannot be convinced that while earthworms may be amicably regarded by farmers, they get between a greenkeeper and his sleep. It was Darwin in 1881 who weighed worm casts and found they produced 10 tons /acre, "a respectable covering of soil". Precisely ! That covering spreads and smothers fine turf, is smeared and flattened by traffic; creates bumpy surfaces; provides entry points for air borne seeds and annual meadow grass; and brings buried seed to the surface. Whereas deworming removes the food for moles, so dewormed turf is free from moles.

Darwin's painstaking observations have always muddied the water whenever earthworm control is discussed. Only a few decades ago, control was no problem. One dressing of lead arsenate at seven year intervals not only gave total control but was unarguably much safer to use than frequent applications of less toxic (but less persistent) substances, at intervals of a few months - without taking into account fears about contamination from leaching etc. Anyway, despite the fact that even using it with carefree abandon over 40 years we never lost a single golfer or greenkeeper (and rare cases of stock poisoning were always traced to careless disposal of empty drums). Its use was disapproved of rather than banned. It was virtually insoluble as well as heavy and so neither drifted nor leached, thus contamination was nil.

The situation today is parlous. The casting worms, though a tiny minority of the 25 species which occur in the UK, are still just as much a pest as they ever were but wormkillers are now banned. With the banning of Chlordane (with about as much scientific justification as banning beef-on-the-bone) we are left with three alternatives. Carbaryl, (the use of which is permitted only by tractor sprayer, with the operator in a completely enclosed cab), and two fungicides Thiophenate and Carbendazim, which have secondary and far from reliable side effects on earthworms.

Clearly we are going to have to prepare for pest control without pesticides in the future. Earthworms love lime in any form and will not invade acid turf at a pH below 4.5. Just look at the old (limed) white lines on an abandoned (acid) tennis court - heavy casting and associated intensive weed invasion, confined to a narrow strip. Therefore we must keep the pH low, partly by avoiding alkaline reacting materials and in extreme cases by acidifying the soil with sulphur or its derivatives.

Sulphur has been used in powder form on wormy wet clay soils for more than 65 years - with dramatic effects in discouraging worms and improving soil drainage by flocculating clay particles to give bigger spaces both for drainage and roots. The only problem with sulphur is that it is impossible to guess (or analyse soils to determine) the correct rate, as this varies with individual soils. Thus a trial for 6-9 months is necessary to determine the optimum rate. Do not be too hasty in deciding - the higher rates give the quickest results but in a few months can leave bare soil or at best scorched turf.

Another management tactic which helps is to starve the little pests. They live on decomposing (not fully decomposed) matter, which is why one sees fallen leaves pulled down their burrows. In problem areas, even fairways, always collect the cuttings - they are manna to earthworms. Never, of course, lime turf, even the most acid soils, for in addition to worms and weeds you will get severe attacks of take-all-patch disease.

All greenkeeping is swinging back to the theme of avoiding problems rather than waiting for them to show and then hitting them. Quite apart from the cost, there is the disturbance to the balance in soil ecology. No parasite wants to kill its host or it will die too. We should tolerate some 'beasties' that eat at our table - it is only when they get too uppity that their presence is intolerable.

In many cases, the over-the-top unacceptable activity of pests has been encouraged by our messing about with the equilibrium of the environment. A classic case is that of fusarium patch - fus - which lives quite happily and inoffensively as a saprophyte on dead tissues, until something happens to make it think it is Christmas. Far better to ban Autumn fertilisers; make sure the dew is switched every morning; improve ventilation; avoid letting grass grow too long; take steps to counteract sand blasted out from greenside bunkers; and apply top dressings only when there is growth to absorb them, rather than rely on constant dosing with fungicides. Indeed, with fus there is a proven case for using biological controls, e.g. an inhibitor which suppresses this disease by encouraging a predatory soil bacteria Actinomycetes, if it is applied in late Spring and very early Autumn. Yes, it sounds all muck and magic but I know from my own experience over the past three seasons that it does work and does not upset the 'greens'.