In situations where you can’t get to your land to do a nightly slug pick and you’re only option is some sort of control is it better to use pellets or nematodes? If anyone has done this experiment let us know. Up until a couple of years ago the choice was between chemical slug pellets and organic biological control, but now there is a soil association approved organic slug pellet on the market – Advanced Slug Killer – we can have a look at both of them. I haven’t used either so I’m reporting second hand here.
Organic slug pellets are based on ferric phosphate, which according to reports will break down harmlessly to iron and phosphate nutrients after use and do not harm children and pets, birds, hedgehogs and other wildlife. They only kill slugs and snails.
Organic slug pellets are a poison but are allowed under organic standards because they are made using base chemicals found in nature. Nemaslug is the product name for Phasmarhabditis hermaphrodita – a natural predator of slugs that looks like a microscopic worm.
A parasitoid, nemaslug enters the slug and feeds off it from the inside, causing the slug to lose its appetite and eventually die. These are found readily in nature but the nemaslug product allows you to apply a concentrated dose to kill as many slugs as possible in the area you wish to garden, or farm.
So what are the advantages and disadvantages. The advantages of slug pellets is that they have a shelf life, can be pre-ordered and kept in storage ready to use when a situation calls for it.
The disadvantage of nemaslug is that it has no shelf life. The nematodes are bred in a lab, take a few days to reach you once an order is placed and must be used straight away. You must plan when to use it and it needs to be reapplied every six weeks. It kills young slugs living below the surface of the soil (90% of the population) but not the big ones on top.
Because it is a soil based nematode it also does not kill most snails, which live above the soil. Slugs can be particularly harmful to potatoes and other root crops. Many people say it is very important to rotivate the soil regularly to disturb and kill slugs and slugs eggs.
Slug pellets on the other hand kill those slugs and snails that are moving about above the surface. They work because they contain an ingredient which slugs find attractive. Slugs eat the pellet, not suspecting that it contains poison.
I have not found any comparison studies between the two but Gardening Which? found that 72 per cent of people taking part in a test believed nemaslug an effective way of controlling slugs.
Having said this only 42% said it was more effective than their usual method and only 38% would buy it again. Many people thought it too expensive, complained that it didn’t control slugs and was a pain to apply. There is another problem too.
In another Gardening Which? study they found that some biological control companies failed to deliver the promised number of nematodes. This meant that applications were less successful than they should have been, and that customers were getting poor value for money. The best companies for slugs were Agralan and Defenders but it should be noted that Defenders did badly on other biological controls. The worst Green Gardener and Scarletts. They didn’t review the Organic Gardening Catalogue.