A pest free organic garden does not exist. There is a constant battle between the pests and us for the food. Keeping your soil healthy and your plants well nourished should help. Weak plants will attract pests.
If you do resort to insecticides or natural pest repellants never spray onto flowers or you could poison benficial insects visiting the flowers.
Many pests find their favourite plants by smell. Plant strong smelling plants such as alliums next to carrots or cabbages. Garlic chives are very useful, add a seed or two in the same pot when starting off cabbages.
Marigolds are also a strong smelling plant that will self seed throughout the plot.
Sacrificial plants can lure the pests away. We have nasturtiums and red orach mountain spinach which pop up all over the plot. These catch lots of green and blackfly which might have otherwise attacked our beans for example.
Barrier methods such as covers over the whole crop or discs around the base of the plants can be used.
Planting at certain times can really help with pest control. Use autumn planted broad beans, the plants will be stronger by Spring when the blackfly are about.
Companion planting using a range of plants will encourage beneficial insects such as lacewings, hoverflies and ladybirds. Nature if given the change will provide the solutions, somewhere there is an answer in the food web.
Aphids (blackfly, greenfly)
Aphids love new growth especially tender bean tendrils. I often spot them because of increased ant activity on the plants.
I can manage to squidge these and have tried a soapy solution spray. 1 tbs of Castille soap in 1 litre of water (cayenne pepper or cinnamon can be added but it does clog up the spray bottle). Although the spray is said not to harm ladybirds or bees I would use as a last resort. An infusion of nasturtium leaves can also be sprayed on.
Using sacrificial plants such as orach or nasturtiums has decreased the number found on our crops.
This year 2021 we have managed to control the blackfly with the help of ladybirds. Hoverfly larva will also enjoy the aphids. Planting flowering plants will provide pollen and nectar to encourage beneficial insects.
The nasturtim here has done its job as a catch crop for black fly
The plant will need to be pulled up or the blackfly will find their way to the beans
I don't mind the birds they help with other pests so we don't use bird scarers like spinning CDs and DVDs or a scarecrow. If I do need to protect I will use netting such as over the gooseberries but check regularly as birds and other wildlife can become tangled.
Use netting and inspect your crop regularly.
Cabbage Root Fly
We don't often grow cabbages, this year 2021, will are trying again. A cardboard collar about 10 cm wide around the base helps but can attract slugs.
Carrot Root Fly
This is a problem at our allotment so if I do grown carrots its at home in the raised trough. Intercropping might work at the allotment. Something for us to try in the future.
It might not be slugs eating holes in young plants! Use a rolled-up water soaked newspaper and leave out just before dark. Early the next morning collect the newspaper and hopefully the earwigs.
Flea Beetle and Leaf Miners
Although the damage is annoying I'm happy to eat leaves affected. We don't suffer too badly.
Rabbits (and Deer)
These can be a real problem in some allotments. Good fencing is important. You could consider digging down a wire fence around your individual plot if they are a problem. Even though we are surrounded by fields and the boundary fence isn't good we luckily haven't had a problem with rabbits.
Slugs (and Snails)
Slugs love cool, dark, moist environments and love moist mulch, so what do you do?
Handpick slugs off? But what do you do with them then? It is suggested to drown them in soapy water, I can't do that. I read that 95% of the slug population is below the ground!
I have had success with making plant collars from a plastic bottle by cutting 5cm sections across the diameter.
Comfrey leaves around the base of plants and renewed weekly.
I really dislike using slug pellets even though they are labelled organic. Nemaslug a biological control but isn't suitable for the clay soil we have.
Other ideas are eggshells scattered around the base of the plants but I've found snails love them and slugs don't care about crawling over them.
Natural slug predators are frogs, toads, snakes, newts, hedgehogs and ducks. Fortunately we do have the first three. We have an old compost bin with sticks in that several grass snakes live in. I'm hoping to make some more grass snake habitats around the allotment to see if that helps.
I don't sow directly into the ground at the allotment and introduce plants at a later stage when they are not so appealing to the slug.
The grass is kept short so there are less hiding places next to the plots.
Apparently leopard slugs will actively hunt for normal slugs to eat them. They can travel at a top speed of 15cm per minute which is much faster than other species of slug.
These are leopard slugs enjoying the food in the cat's bowl.