Pest and disease management on organic allotments.

In order to keep plants healthy good soil management is paramount.  Large amounts of organic matter can be added to the top soil to increase the soil microorganism population.  This will increase predators such as the soil centipede, Stigmatogaster subterranean.

Soil centipede

Adding horse manure to potato bed
Manure laid over the topsoil and left for several months
during winter

Manure dug in in February
Digging over the soil exposes the surface to birds, which can take off top soil pests.  Encouraging birds by using feeders and nesting boxes will increase the population of birds visiting the allotment and also their usefulness in removing pests. 

Seeds in feeder to attract birds
Bird feeder on the pear tree.
Green manure covering the allotment over the winter will protect the soil from excessive leaching and give a habitat to small predatory animals.   

Green manure of rye, tares and crimson clover
The brassicas bed is limed to increase the pH of the soil and discourage club root.  

Predatory insects such as ladybirds and lacewings are attracted to the allotment by habitat boxes. Immature larvae of ladybirds and attractants for lacewings can be bought on the internet.
Lacewing box 

Amphibians like toads and frogs, which are predatory on slugs and snails, can be encouraged by creating a pond habitat for them to breed in.

Pond for amphibians

There are several natural predators of slugs and snails.  The ground beetle is one of them and I go around looking under logs and stones to try to catch as many of these as I can to put onto the allotment.  They need a home to live in such as under planks of wood or ceramic plant pots.  I have put loads of toads on the allotment but I can never get them to stay.  I would love to have both slow worms and hedgehogs on the allotment but sadly I have never had that luxury.

Thrushes used to be the very best snail predator.  They have used paving slabs on the allotment as their anvil to break open snail shells.  Anything that will attract natural predators will help in the control of slugs and snails.

I have built a hedgehog box and put it in the hedge at the bottom of the allotment.  I live in hope.

In the yearly planning of an allotment resistant varieties such as Fly Away carrots, which are resistant to carrot root fly and Clapton cauliflowers, which are resistant to club root,  can  be looked for in the catalogues. 

Planning a rotation of vegetables each year reduces the buildup of pest and diseases in particular areas of the allotment.  Brassicas are particularly sensitive to club root but a good rotation of more than a three year cycle will go a long way to prevent its build up in the soil.  I have a six year rotation cycle but, with the new half allotment, I can make this even longer.

Barriers can be used against several different pests.

Chicken wire around peas will help to keep
pigeons from eating the foliage.
Scaffold netting over the brassicas
Scaffold netting will keep both pigeons and cabbage white butterflies away from the brassicas.

Enviromesh over the carrots to keep carrot
root fly away from the plants.   
Bordeaux mixture of lime and copper sulphate can be applied in late June to prevent blight.
Potatoes in late June sprayed with Bordeaux
Nematodes, predators of slugs and snails, can be applied in six week intervals.


I use Nemaslug nematode Phasmarhabditis hermaphrodita worms spraying them only in areas where I know snails and slugs congregate.  While this is not 100% effective, it does seem to have reduced damage and the breeding adults so that there are fewer eggs to overwinter.

While I can understand the agonizing that many of us undergo when attempting to produce food that is grown with as few human made chemicals as possible, we must be reasonable.  The slug and snail pellet ferric phosphate FePO4 is indeed an inorganic chemical.  This means, in chemical terms, that it does not contain carbon.  Confusion comes when we apply the term organic to gardening.  Organic in biology means related to life or organisms.  If we replace the metal iron with the metal calcium in this compound we get a major component of bones -  calcium phosphate, which although making bones is an inorganic chemical.  Does this mean that the strict advocate of organic gardening should not use blood, fish and bone as a fertiliser?  I don't think so.

I would prefer not to use ferric phosphate as a slug and snail killer because I would rather remove as many slugs as I can by hand - gloved if possible.  There is little evidence about the effect of ferric phosphate on other soil organisms and is probably best avoided if you are trying to be organic.

As the gardener Percy Thrower used to say a tidy garden is a good garden.  If there is no habitat for the molluscs to live in then there will be fewer of them.

If you are going for the hand collection method it is easier if you use traps like upturned flower pots, upturned orange or grapefruit skins or planks of wood.  I have seen people use newspaper soaked in sugar solution and covered with a plank to attract slugs and snails.  These methods may serve to attract slugs and snails but I use them regardless.

Beer traps are also effective and so too is a diluted honey and yeast mix.  There are other recipes such as sugar, flour and yeast or just diluted sugar solution and yeast.

Introducing mychorrhiza when planting may improve the health of plants and healthy plants are more resistant to pests and disease attack.

It is important to keep the allotment tidy and remove all dead, diseased or damaged plant material from the allotment.  Sometimes, for example, leaves infested with aphid can be sprayed with water to remove them but if they are persistent then the leaf can be taken off and composted.

So, many different methods of pest and disease control that can be used without resorting to man made chemical sprays.

However, the best way of keeping plants healthy is to provide them with optimal growing conditions and keeping the allotment very tidy.      

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