Malachite Green 
A green dye material (being a chloride salt) which was diluted and added to different substances, one of which was Bordeaux mixture for use as a fungicide in the mid-20th Century. It was also used as a treatment for controlling fish diseases however, it is also toxic and a carcinogen, being banned from use in the UK from 2002.
Metaldehyde
A molluscicide for the control of slugs and snails. This pesticide was withdrawn for sale and distribution from 30 June 2019; and authorisation withdrawn for the disposal, storage and use of existing stocks by 30 June 2020.
Methyl Bromide
A soil fumigant which was previously used to disinfect soils of Type 1 Fairy Ring and which is no longer approved (from 2005?) for sale or use in the UK, being banned in accordance with the Montreal Protocol on Substances that Deplete the Ozone Layer.
MMC Pro
A biocide for use on hard surfaces, as well as artificial sports surfaces, for the control of algae and mould. It contains didecyl dimethyl ammonium chloride (8.9% w/w) and has an application rate of 1 litre of diluted product per 3-7m², using either 1-part concentrate diluted with 4 parts water for normal use, and 1-part concentrate diluted with 9 parts water for light growth. It is manufactured by Brinton Products and marketed by numerous suppliers.
MossOff
A non-synthetic chemical moss and algae removal product for lawns and hard surfaces. The active ingredients are lactic acid and potassium sorbate. After spraying on moss, or algae, the substance must be allowed to dry for 24 hours without being washed off by rainfall. This helps to form a biodegradable micro-coating that acts as a barrier to moisture and nutrient being absorbed by the leaves, which will turn a straw brown colour over 7-10 days, eventually being killed off and allowing scarification to take place after about 2 to 3 weeks to remove the dead vegetation. It is manufactured by the VivaGreen group.
Mowrah Meal
A former pesticide used for the control of earthworms. It acted as an irritant for the earthworms, expelling them from the soil and then needing to be swept up and removed from the area.
Murvin 85
A product name for an insecticide which also acted as a lumbricide that contained the active ingredient carbaryl, as a wettable powder, for the control of chafer grubs, leatherjackets and suppression or temporary control, rather than any longer-term control of more than a year, of earthworms but is no longer approved for use.
Mycorrhizal Seedcoat
A zeolite or volcanic rock carrier which contains spores of beneficial mycorrhizal fungi, growth promoting bacteria, fungi and organic soil nutrients. The product should be mixed with seed and sown as normal. Fungicides should not be applied to the turf or soil area for a period of two weeks before or after sowing. The suggested minimum application rate is 3kg of product per 10,000m2 (or 0.3g per m2). If, for example, a sowing seed of 25 g/m2 is required and 800m2 is to be covered (which is a full 20kg bag of grass seed), then this would require 0.24kg of the Mycorrhizal Seedcoat to be mixed
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Napthalene
A slightly toxic chemical compound which was used during the mid-20th Century as an insecticide to control leatherjackets.
Nema-Go
A combination of essential oils and proteins, which is not phytotoxic, and which acts as a nematode repellent. The application rate is 20 ltrs/ha every 15 days for three applications, and then 10 ltrs/ha each month after the initial applications. This is supplied by Agronomic Services.