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How to kill WORMS...
GRAHAM PAUL, of Sherriff Amenity, offers some advice on how to get the best from wormkillers
THERE is some controversy regarding the worm control products that are used in the turf industry today. This article is intended to help clarify some of the issues involved in the use of these chemicals. Many years ago I worked for May & Baker, developing new products for the amenity market. Amongst the projects I was involved with was a worm control product called ‘Castaway’. This was originally formulated from thiophanate ethyl, which is a precursor of the worm control products we use today (carbendazim - also known as MBC).
Thiophanate methyl and thiophanate ethyl break down rapidly to form MBC and it is MBC that gives the product fungicidal and worm control properties. To get the best control
from products based on MBC such as ‘Caste Off ’ or its precursors based on thiophanate methyl (‘Mildothane Turf ’ and ‘Snare’) we have to understand a little of the biology of the earthworm.
Earthworms play an important role in the development and maintenance of soil structures. They live in burrows that can be several feet deep with some species and this can provide useful aeration of the soil. As they play out their lives, for the most part hidden away from us, they consume large quantities of soil and decaying plant material from which they obtain all of their nutrition. The waste material, a well mixed, highly fertile compost, is excreted in the form of ‘convoluted tubes’ which we refer to as worm casts. Not all worms excrete their casts on the surface. Of the 25 species found in UK turf, only 3 are known to deposit surface casts. The remaining species release their casts underground, so avoiding all of the mess and misery experienced by the groundsman and greenkeeper!
Although most earthworms feed on decaying plant roots and organic matter found below the soil surface, the
surface casting species will also collect leaf material from above ground and take it down into the burrows where it is eaten. It was this phenomenon that first led us to the worm killing properties of MBC. In the 1970’s one of the biggest selling fungicides for use in apple orchards was ‘Mildothane’ as it was effective against powdery mildew, apple scab and also controlled red spider mite. It is a well known fact that earthworms will completely clear the fallen leaves from an orchard floor during the winter months but, after ‘Mildothane’ had been used for two or three seasons in apple crops, we began to notice that the leaf litter was not disappearing from orchards as usual. Investigation revealed that the surface feeding species were absent from soils of treated orchards and it was concluded that they had been killed by the residues of thiophanate methyl left on the leaves from repeated sprays throughout the
growing season.
Some people believe that MBC (carbendazim) doesn’t kill worms but just suppresses casting for a few weeks. In fact, evidence shows that MBC does kill worms that feed on the surface and that the surface feeders are responsible for casts deposited above ground. In our field trials with ‘Castaway’ we extracted all of the worms from treated and untreated plots and then counted the number of each species present. Extraction was achieved by pouring diluted formaldehyde solution onto the soil. This irritates the worms and they rapidly emerge from their burrows. The surface feeding/surface casting species were absent in the treated plots but were found in the unsprayed plots. We also counted worm casts in the sprayed and unsprayed plots and were able to demonstrate that casts were absent in the treated areas. Please note I would strongly advise readers not to use formaldehyde on worm infested turf as it kills the
“I would strongly advise against using formaldehyde on worm infested turf areas as it kills the grass”
asked!
Well you
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