Common pests and diseases

Information sheet

Finding pests & diseases in your garden can be worrying. Follow this simple guide and you can identify the culprits and find a solution.

Common pests in the garden

Aphids including blackfly, greenfly and whitefly

These are sap feeding insects, which infest shoot tips, flower buds and the underside of younger leaves. Feeding causes distortion to the plants and sometimes the affected area can wither and die. These insects also carry viruses through their biting mouthparts. Viruses can weaken the plant and cause stunted growth, leaf fall or other abnormalities to the flowers and leaves. For these two reasons it is best to remove aphids from your plants when they first appear. Aphids have many natural enemies in the garden, including ladybirds, lacewings and hoverfly larvae. Attracting a wide range of wildlife in your school garden will help with nature’s battle to keep numbers of the pests down to an acceptable level.
Methods of control include removing the pests and squashing them with fingers or spraying with a mild soap solution. Both of these should be carried out by an adult not the pupils. A biological control using parasitic wasps can be purchased. This is especially useful for controlling pests in glasshouses.

Caterpillars

All children know that caterpillars turn into beautiful butterflies and moths, which we love to see in our gardens. When your entire cabbage crop has been decimated by caterpillars however it’s a different story! Caterpillars often feed on a specific crop - such as peas or cabbages.
Methods of control include inspecting plants regularly and picking off caterpillars where seen. Use a pathogenic nematode as a biological control. These nematodes enter the caterpillars' bodies and infect them with a bacterial disease.

Birds

Many larger birds can be a problem in the fruit and vegetable garden. They eat the emerging leaves and damage parts of many plants including brassicas and peas. Birds can also eat or damage ripening fruit such as apples, plums, cherries and currants.
Methods of control include using a scarecrow to keep the birds away (a great activity) or physically protecting the crop using fruit cages, netting or twigs.

Slugs & snails

Slugs and snails are so abundant in gardens that a certain amount of damage should be tolerated. You will want to protect your most vulnerable plants from damage or destruction. Both molluscs feed by rasping plant tissues with a toothed tongue. Slugs remain active throughout the year, whereas snails are dormant in autumn & winter.
Methods of control include covering young plants or seedlings with cloches or physical barriers, and encouraging more wildlife in the garden such as thrushes, toads and hedgehogs. Snails can be safely picked off and moved to an area outside the school garden. Use a biological control containing the nematode specific to slugs.

Weevils

Vine weevil cause damage to plants in their larval and adult stages. The larvae feed on the roots of plants, especially those in pots or containers. The symptoms are similar to those of over or under watering plants as the roots are severed and unable to obtain water. The adult beetles feed only on foliage, causing notching on the edges of leaves. They are particularly fond of strawberries.
Control methods include picking off adults on warm evenings or trapping them with sticky traps. Encourage natural enemies (other wildlife) in your school garden such as birds, robins, frogs & toads. Use a biological control containing nematodes that specifically target vine weevil grubs.

Rabbits

Rabbits feed on a wide range of garden plants. New shoots and foliage can be grazed down to ground level, trees can be ring-barked and holes & scrapes dug in flower beds and lawns.
Methods of control include: fencing young trees and shrubs when first planted. The bottom 30cm should be buried below ground level to deter rabbits from burrowing underneath. Cover young vegetable plants with cloches.

Diseases in the garden

Rust

The rusts are a group of fungal diseases affecting the aerial parts of plants. Leaves are most affected, but rust can also be found on the stems, flowers and fruit. In the vegetable garden rust is commonly found on leeks, onions, garlic and chives. Pustules are found on the lower leaf surface and produce huge numbers of microscopic spores. Mild infections do not render the vegetable inedible but in extreme cases leaves die and the yield can be reduced. Control the disease by spacing plants at the correct distance. This improves air circulation and stops the spores spreading onto neighbouring plants. Remove and dispose of infected plant parts as soon as they are seen (not in the compost heap).

Powdery Mildew

This disease is shown by a dry, whitish powder coating leaves, shoot tips and sometimes flowers. Other symptoms include stunted growth and reduced flowering. Plants that are particularly prone to the disease include courgettes and Phlox. Remove and dispose of infected areas as soon as they are seen, but not in the compost heap. Powdery mildews are associated with water stress in plants.
Control the disease by planting at the suggested spacing to increase air flow around the plants, and ensure they are sited in their ideal growing conditions. Keep plants well watered at the roots and mulch the area to preserve moisture.

Damping off

This affects seedlings both inside and outside and is caused by several different fungi. Seedlings collapse then die and can become covered in a white mould. The disease can strike below the compost causing an apparent failure to germinate. Cool, humid conditions and overwatering can make the problem worse. Control the disease with good horticultural practices; always use clean containers and fresh, sterile compost. Water seedlings with tap water only and not from a water butt, and sow seeds thinly, so they are not over crowded.

Diseases in the garden

Blight

Blight is a fungal disease that is specific to tomatoes and potatoes, it is most common in wet weather and the infecting spores are carried by the wind. It affects the foliage and fruit of the plants and can cause rotting and eventually death of the infected parts.
Control the disease using effective crop rotation, not growing tomatoes and potatoes too close to each other or on the same area two years running. Early cropping potatoes are more likely to escape the problem. Infected plant material should be removed and not composted. Some varieties show resistance, but will eventually succumb in warm, wet weather.