Common Pest and Disease Problems - Protect your patch

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Common pests can be nothing but a nuisance in your vegetable garden and can significantly damage the quality and yield of your crop. This can make all the effort seem less worthwhile so it’s important to protect your plants.

There are various ways of protecting your veg. patch from pests. Prevention is better than cure: For a successful crop it’s important to plan for the season, consider the problems you may have with pests and find something that will deter them before they cause any damage.

Pests such as pigeons, rabbits and mice find the convenience of a veg patch irresistible, luckily there are ways to stop them from getting to your plants:

  • Netting. Use a poly-net tunnel to cover your veg, this way they still benefit from good air circulation but the pests cannot get in to nibble the plants. This is especially effective for deterring birds and butterflies.
  • Fencing. A simple chicken wire fence is sufficient to keep the rabbits out as long as it is properly secured around the base with strong pegs.

For quick reference please see the pest and disease guide below. In addition below the reference guide you will find some suggestions for companion planting a method of growing one plant next to another to ward off pests.

Common Vegetable Diseases & Pests












Infestation of black and yellow leaf eating beetles

Asparagus Beetles

Remove by hand or use a contact insecticide such as thos based on fatty acids


Beans, cucumber, lettuce, potatoes

Leaves turn mottled and disfigured with a yellow mosaic pattern. Flowering is reduced, plants are languishing bean pods turn black

Mosaic virus or cucumber mosaic

No cure, remove and burn all affected material. Plant replacement crops elsewhere


Beans, cucumber, tomatoes and container grown veg

Plants wilt and die, roots turn black.

Root Rot

Prevent by crop rotation, use sterilized compost and water with mains water only not water stored in water butts. Destroy any diseased plants and remove soil from around the root area which will harbour spores


Brassicas esp cabbages

Stunted growth and wilting, little white grubs boring into roots

Cabbage root flies

Prevent flies getting access to the plant by covering with fleece and/or fixing collars around stems when planting out.



Leaves covered in small, eaten holes

Flea Beetles

Protect with fleece or fine mesh to prevent them getting access. Done during spring you should then be able to remove for the late summer.



Plants are stunted and wilted, roots are distorted


Prevent by adding lime to soil approximately 4 weeks before planting and applying strict crop rotation. Once plants are infected there is no cure – pull up and destroy all effected plants.


Brassicas, courgettes, lettuces, onions

White fluffy spots on underside of foliage and mottled effect on top side combined with stunted growth

Downy mildew

Choose disease resistant varieties, crop rotate and leave plenty of space between plants. Remove effected material and burn. Spray with copper based fungicide.


Brassicas, courgettes, lettuces, onions

White fluffy spots on topside of foliage and eventually stunted growth

Powdery Mildew

Consistent watering as stress caused by under-watering or inconsistent watering frequently allows Powdery Mildew to get a foothold





Brown tunnels eaten into carrot roots.

Carrot Root Flies

Sow in early summer to avoid flies, cover with fleece or erect a barrier 1m high as they are low flying. Sow with onions or garlic as the smell repels them, avoid disturbing the soil as the flies are attracted by the smell of carrots.


Courgettes and other greenhouse / conservatory plants

Yellowing and unhealthy coloured leaves. On close inspection small webs are visible.

Red Spider Mites

Mist regularly as they thrive in dry conditions. In extreme cases try using a spray containing bifenthrin.



Leeks, onions, potatoes, tomatoes

Leaves wilt, turn spotted and/or stems swell up and are deformed.


Choose resistant varieties and apply good crop rotation. Remove and burn effected plants.


Leeks and onions

Poor growth and yellowing leaves. Root and bulbs eaten as larvae tunnel into bulb. Bulbs usually rot.

Onion flies

Protect seedlings with fleece and crop rotate. Remove and burn effected plants.

Potatoes and Root Vegetables

Wilting foliage, roots and tubers contain large numbers of small bore holes.


Apply good crop rotation techniques to avoid build up of the pest. Keep area weed free. Lift crops early to avoid excess damage. In severe cases grow potatoes in large pots instead of open ground.


Potatoes and Tomatoes

Brown patches on leaves leading to rot - especially in wet seasons


Choose disease resistant varieties, spray with a copper based fungicide in very early stages. Remove and burn plants in later stages.



Scabby growths on the tubers

Potato Scab

Choose disease resistant varieties, clear away plant debris in autumn and operate strict crop rotation system.


Strawberries and Tomatoes

Grey fluffy mould patches on leaves (stems in tomatoes) and fruit.

Botrytis also know as Grey Mould

Brought on by consistent damp cool conditions and in strawberries any contact with the soil. Keep greenhouses well ventilated and prevent fruit contact with the soil by mulching. In tomatoes a regular spray with Bordeaux Mix will offer good protection.



Black patches on the underneath of the tomatoes which then rot

Blossom end rot

Caused by inconsistent watering, especially in containers, pots and grow bags. Prevent by regular watering and feeding - no cure for affected fruit, simply pick off and destroy.


Various but particularly problematic in Peppers and Beans

Frequently seen in masses at the growing points of plants or on the underside of leaves. Sometimes the most obvious evidence of an infestation is sticky lower leaves. They are sap sucking pests and cause a general weakening of the plant, transmit viruses and encourage fungal infections.

Aphids otherwise know as Greenfly or Blackfly

They multiply very rapidly so early treatment is best by spraying with insecticidal soaps or with a bifenthrin based spray.



Cabbage and most members of the brassica family

Large holes eaten in leaves.

Cabbage White Butterfly and Caterpillars

Pick off the caterpillars by hand or spray with insecticides containing chemical ingredients Pyrethrum or Bifenthrin




Companion Planting
Protect your home-grown fruit and veg. from pests without chemicals!

Companion planting is an effective way of targeting specific pests preventing them from going near your plants without chemical pesticides. Often it’s as simple as planting odorous plants next to your crop to over-power the scent of vegetables that pests find irresistible.

There will always be some bugs that are so determined that they persevere through, but gardeners have used this method for centuries and found it to be a great success in reducing such damage.

Plan your veg. patch with this guide to companion planting:


Veg. Crop


Common Pests


Companion Plants




Carrot Fly


Onion, Coriander, Chive, Rosemary, Leeks






Aphids, Onion Fly, Leek Moth


Carrots, Onion, Coriander, Chive, Rosemary




Cabbage Butterflies/root fly, Aphids


Rosemary, Oregano, Chamomile, Mint, Marigold,
Onion, Nasturtium






Marigold, Coriander





Cabbage Butterflies/root fly, Aphids


Rosemary, Oregano, Chamomile, Mint, Onion



Brussels Sprouts




Marigold, Rosemary,
Oregano, Mint, Onion





Tomato Worm, Aphids
Beneficial insect: Bees -
increases pollination and yield.


Borage, Mint, Coriander, Onion, Pot Marigold








Onion, Marigold, Garlic, Nasturtium






Aphid, White Fly


Pot Marigold, Mint, Nasturtiums, Radishes, Carrot







Coriander, Marigolds, Onions





Beneficial insect: Bees - increases pollination and yield.







Aphids, flies


Onions, Marigold, Garlic, Mint












Cabbage Butterfly/Worm/root fly


Geranium, Rosemary, Nasturtium


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