Preventing pest and disease problems

As chemical control choices diminish and concerns for health and the environment increase, it’s important to protect your garden from problems.

Pot cleaning

Quick facts

Suitable for: all gardeners
Timing: all year round
Difficulty: easy to moderate

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People are increasingly looking for more environmentally sensitive ways to cultivate plants. There are many common-sense steps you can take to prevent harmful organisms entering or spreading round your garden. Good cultural control, plant selection and encouraging natural predators are especially important.

Choose your plants carefully

Take action to keep pests and diseases out of your garden and protect your plants from damage by considering the following:

Right plant, right place

Plants thrive if they’re in a suitable environment. By selecting the right plant for your region’s climatic conditions it will grow more healthily and be less susceptible to pests and diseases. For example, moisture loving plants will struggle in counties where rainfall is scant. Even within the garden itself, areas offer different conditions (microclimates) such as rain shadows or frosty hollows, so choose and position your plants accordingly.

Consider avoiding problem species

If you have plants you cherish in your garden, but pests and diseases affecting that species are widespread, think carefully before you bring new plants into your garden. Examples include agapanthus (agapanthus gall midge), aquilegia (aquilegia sawfly) and box (box blight and box tree moth caterpillar).

Be additionally careful when choosing plants grown abroad

Supply chains can be long and some plants sold in UK garden centres may have begun their lives abroad. Aim to purchase plants from reputable suppliers produced in accordance with UK plant health regulations. Imported semi-mature trees and shrubs (especially those sold in their native soil) which have not spent a growing season in the UK may carry an increased risk of harbouring exotic pests and diseases.

Ensure holiday purchases conform to the rules

It’s important to be particularly cautious when purchasing plants on holiday abroad. Also be careful buying from private suppliers abroad over the internet.

Select cultivars with resistance or tolerance to pests and diseases

Seed packets and plant labels generally highlight such characteristics. For example, new rose cultivars may offer some resistance to black spot for a period. Some potatoes such as ‘Charlotte’ fend off slugs. In areas with soil infections such as club root, seek resistant brassicas. See our lists of plants that are less susceptible to verticillium wilt, honey fungus and phytophthora root rot to help you avoid plant loss.

Ensure plants you purchase are healthy and thriving

Don’t be tempted by less healthy ones on the discount shelf. They will be more vulnerable to pests and diseases, even if they don’t have them already. If plants are grown well by the producer and cared for by the garden centre, they will get off to a better start in your garden.

Check and monitor new arrivals

Tip out pots to check for root pests such as vine weevil grubs. Before planting out in the garden, consider isolating new arrivals and monitoring their health. This is especially important for plants imported from abroad.

Grow your plants well

Choose the best spot in your garden

Follow the ‘right plant, right place’ mantra and consider the needs of individual plants. Mediterranean plants are more suited to the warmth of home, so site in a sunny spot; woodland dwellers grow better in the cool of dappled shade.

Test your soil

As pH may affect the nutrient uptake by plants, consider a soil test before permanent planting. Undertake every four years for annual or vegetable plots.

Plant well

A little extra care at planting time – teasing roots out of rootballs, firming in and watering - will get plants off to a flying start.  Break up compaction before planting to help drainage and aeration.

Look after your plants

Provide the right amount of water. This will vary through the seasons. Pay special attention to new plants for the first two years while they establish. Most soils provide adequate nutrition for ornamental plants. You may consider a foliar feed later in summer if signs of nutrient deficiency appear, such as yellowing between the leaf veins.

Reduce stress by mulching well

This protects against water loss, may add nutrients and in time, improves soil structure. It can also bury fungal spores like those that cause rose black spot. These may otherwise splash up a re-infect plants. Mulching can also inhibit the spread of root disease and some pests.

Wise practice

Garden in a way that cuts down potential for disease spread and development. This could include ample spacing between plants and avoiding overhead watering. Also consider good air circulation, such as opening greenhouse vents to improve air flow or pruning your apple tree to give an open centre. However such precautions are not failsafes against disease.

Keeping one step ahead

If you monitor your plants and are careful with garden hygiene in specific areas or at particular times of year, this will go a long way to blocking the spread of problem pests and diseases which may be present in the environment.

Look out for seasonal issues and weather-related problems

Anticipate problems such stress-related powdery mildew. Patrol for slugs in damp conditions before holes in leaves occur.

Anticipate specific plant-related pests and diseases

Some pests and diseases have a limited host range, such as downy mildew of lettuce, tomato and potato blight or currant blister aphid. This knowledge may help you take preventative action.

Be vigilant and take preventative action to stop spread

Nip population explosions of insects such as aphids ‘in the bud’ or pick off mouldy leaves as they appear on house plants. Use sticky traps or pheromone traps to see if pest populations are increasing so treatment can be anticipated.

Garden hygiene

Clean tools, pots and disinfect pruning tools: Pay special attention to vulnerable areas like greenhouses, potting benches, knives for taking cuttings, pots and seed trays. Clean muddy boots. Clods of soil moving round a garden, or from allotment to home, can spread soil-borne disease such as club root of brassicas and Phytophthora root rot. Even clothes can act as a vehicle for dispersal of pests and diseases.

Reduce disease potential in stored water: Clean gutters, disinfect water butts and rotate their use. Even so, only use mains water on cuttings and young plants.

Weeds can be a reservoir for problems: They can compete for resources, harbour disease and provide cover for moisture-loving pests like slugs. Some act as alternative hosts for pests and diseases, for example, rosy apple aphids migrate to plantains in summer.

Dispose of diseased materials appropriately: Your compost heap won’t get hot enough to destroy persistent diseases like honey fungus. Some dead plants are best sent to local authority composting sites, buried on site, or burned. See our page on disposing of diseased material. Only stack healthy materials to create nature habitats.

Other cultural suggestions

Practise crop rotation

If you move crops on your vegetable plots each season (rotation), it helps reduce potential accumulation of soil-borne pests and diseases specific to certain crops, for example parsnip canker.

Natural tonics

Some naturally occurring substances, called bio stimulants, have been recorded as having beneficial effects on plants’ defence mechanisms. One example is willow bark mulches that contain salicic acid. Other organisms such as naturally occurring mycorrhizal fungi can help protect plants from root diseases. Adding mycorrhizal fungi on planting may protect the plant, however fertilisers can reduce their activity and the fungi may be specific to a particular host plant.

Soil health

The zone immediately around plant roots - the rhizosphere - is full of beneficial soil microbes which help protect against soil-borne pathogens. They depend on plant roots. Sowing overwintering cover crops creates that root zone habitat which the bare earth of traditional winter vegetable gardens does not. Using mulches also supports these communities.

Timeliness

Prune during the right season for the species. For example, stone fruits such as cherries are best pruned in late spring or summer when the risk of silver leaf infection is less.

Some problems may be avoided by changing planting or harvesting times

For example, in heavy soils where slugs abound, grow well-chitted, second-early potatoes. These will be ready for harvest before the late season wave of slugs. Lift and store potatoes rather than leaving them to be attacked.

Pruning methods

Many fungal diseases such as box blight infect more easily in wet conditions, so prune in dry weather. Use sharp tools to create clean cuts that heal quickly.

Barrier methods

Take action by physically protecting crops. This might be shelters on your nectarine trees to ward off infection by airborne spores of peach leaf curl. Barriers keep off pests too: felt discs at the base of brassicas can prevent cabbage root fly attack and grease bands on fruit trees decrease egg laying by winter moth caterpillar.


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