Pests and Diseases at the Allotment

Allotment growing is extremely rewarding, however; from time to time, we encounter pests and diseases. Sometimes these are minor inconveniences and other times they can devastate a whole crop or crops.

On this page we will advise you about the most common pests and diseases found on plots and gardens in the UK; particularly those that love feeding on fruit and vegetables that are growing - as much as we do! 

Firstly, we will discuss ways to help eliminate these problematic pests and diseases. Prevention is better than cure; or ways to help control it or reduce it.

Essentially, we encourage natural and organic ways to deter pests and disease as well as treating any outbreaks although there are chemical bug killers and treatments on the market. 

A good way to start is to encourage 'good bugs'. The ladybird, for example, eats aphids. There are positives to having certain insects and wildlife on the plot as they will clean up for you as part of nature's lifecycle. You can create habitats and plant certain plants that will attract these good insects to your plot. We have more information about this on our Wildlife on the Allotment page.

Netting, mesh, cages and barriers can all help prevent birds and insects from accessing your crops.

Another natural method is the companion planting method. There are plants that work well together; where one plant may attract unwanted pests, the other will help deter them where the pests do not like it. We have more information on our Companion Planting page.

There are ways to manage your soil to help prevent infections. Keep your soil healthy by digging in compost and organic matter.  Bio-active compost can suppress soil-borne diseases. Add more to plants where you first detect root problems. We talk more about soil and soil types on our Soil page.

Apply the crop rotation method because plants from different families have differing nutrient up-takes and it helps deplete minerals deteriorating in the soil. We have more information on our Crop Rotation page.

Nowadays, seeds and plants are readily available in resistant varieties, which will help increase your healthy crops and will minimise losses.

If you have to remove infected plants, never compost them. Dispose of them by burning them (if your site permits). Infected or diseased plants that are composted will spread the infections when you come to use it. We have more information on composting on our Composting page.

Allium Leaf Miner

This can affect onions, garlic, leeks, chives and shallots. Leaf mining flies lay eggs and the maggots eat into the bulbs, leaves and stems leaving lines of white mines on the leaves and brown pupae in the stems and bulbs. This can then show signs of rotting when the initial attack has caused bacterial and fungal infections.

Remedy

You can use mesh to help stop the flies' laying eggs, which usually happens during March-May and then September to November. Try companion planting and the encouragement of beneficial insects to control it. You can try a natural spray by blending and mixing hot peppers, onion, garlic and water with a little organic liquid soap.

Ants

Ants are infested with Aphids and are transported to other crops in search of honeydew secreted by them, Ants also build under and over the soil nests and can damage and destroy roots and plants.

Remedy 

Boiling water or Derris liquid will eliminate ants' nests.

Birds

Birds; particularly pigeons will eat everything that we like to eat and so little you are growing is safe.

Remedy

You can use netting and traditional scarecrow techniques, hanging objects that make a noise in the breeze is an effective deterrent. 

Cabbage Whitefly

These little white flies are usually found on the underside of the leaves of brassica vegetables and are not the same as Glasshouse whitefly, which do not infect brassicas. Cabbage whitefly also leaves a sticky residue, resulting in black mould spots.

Remedy

Fine mesh helps protect the brassicas and wasps love to eat them too. You can spray them with a little organic soap mixed with water.

Club Root

This affects the roots of brassicas and often occurs during late summer in wet and warm conditions. You may notice a stunted growth, blue/purple tinged plants and wilting.

Remedy

Adding lime to the soil can help reduce club root. You can also add collars to the base of your plants. This prevents cabbage root fly laying eggs in the soil. Ensure there is no contamination from footwear, tools and so on.

Glasshouse Whitefly

This is not the same as cabbage whitefly and mostly affects plants living in greenhouses or under glass - hence the name. They are tiny white flies that are visible and easy to spot quickly. They tend to leave a sticky substance, which allows black mould spots to grow.

Remedy

Giving the greenhouse a thorough clean and remove unwanted plants. Spray with organic soap and water. Wasps also like to eat them.

 Leaf Rust

As the name suggests, rust-like fungal patches on the leaves and occasionally on stems and fruit too. It is not always a rust colour either, it can be orange, yellow, brown, black or white.

Remedy

If you have caught this early, you can remove the infected leaves without the crop being harmed. Do not compost the infected areas. Avoid watering on the leaves.

Nematodes

Also known as eelworm or onion eelworm, this mainly effects the allium family but also can affect carrots, parsnips and beans. Signs you have nematodes are dying seedlings, poor or stunted growth and swelling bulbs. Unfortunately, it is usually discovered towards the end of the growing season.

Remedy

You can 'suffocate' them by adding layers of composting matter onto the soil and by pouring non aerated water. General good hygiene will help prevent them and leave infected soil bare until the nematodes die out.

Potato Blight

This can occur during late summer, after wet and warm weather. It is classed as a fungal disease.  The leaves will go dark at the edges with white mould at the edge of darker patches.

Remedy

Remove foliage quickly when it is first spotted and wait a fortnight for spores to die off in the soil and harvest your potatoes. Some may be saved but if they are left, there will be no saving them; the tubers and roots can rot. This can also affect tomatoes.

Powdery Mildew

This will appear like white, powder on the leaves, flowers and fruit, and can leave young plants very vulnerable and weak. This can affect fruit trees and bushes, peas, courgettes, cucumbers and turnips.

Remedy

Remove and destroy infected leaves or fruit and mulch well, prune fruit trees and bushes for air circulation and do not over-water or water over-head.

Tomato Blight

Dark patches will appear on the stems and fruit and there will be leaf rot. It quickly takes hold and destroys the whole plant.

Remedy

If spotted early, you may be able to pick some healthy tomatoes, unfortunately there is no cure for blight and foliage should be burnt to avoid spreading the disease.