Keeping your plants healthy by good cultivation and sanitation is the best way to prevent pest and disease problems. But despite our best efforts, some diseases can blow in or the weather encourage an increase in populations of problem species.

Diseases are especially difficult to control once they take hold. The vegetable and fruit garden is of special concern. Here, there are very few fungicides available for home gardeners to treat fungal infections of edible crops, even if they wanted to.

There are ways to manage insect and disease problems in your garden without the use of pesticides, here are some ideas to help:

Be patient

Insect populations can rise and fall. Damage may be tolerable if merely cosmetic. Insects are part of the garden ecosystem and will be helping to support the presence of other animals.

Be vigilant and monitor

Nip populations in the bud before they boom. Use sticky traps or pheromone traps for insects such as whitefly, codling moth and plum moth. Traps may not kill large numbers, but they do play a role in monitoring population rises. Knowing the biology of the insects that may be present can be helpful; bear in mind that some insects may spread diseases such as viruses. If plants are young and more vulnurable then they will want to be monitored more frequently.

In the case of Integrated Pest Management (IPM) - a strategy that uses a combination of techniques to reduce damage - traps are used as a way to minimise chemical inputs, as they can help to time management strategies.

Mechanical removal

Wash off colonies of insects such as aphids (greenfly) with a hose; pick off invertebrates like slugs by hand.

Encourage beneficial insects

Insects such as hoverflies predate on aphids, so grow plants that attract them into your garden. Hoverflies have short tongues so open flowers such as those in the daisy and umbellifer families, which have easily accessible pollen and nectar, are best.

Introduce predatory or parasitic organisms

In greenhouses, conditions can be controlled and there is an array of living products to choose from for keeping pests at bay. Outdoors, choice is more limited, and timing to match the vulnerable stage in the pest’s lifecycle is critical, for example nematodes with vine weevil.

Heat treatments

These are used mainly to combat nematodes in bulbs and herbaceous perennials. Hot water treatment can be used against both white rust and eelworm in chrysanthemums. Very precise timings and temperatures are required.

Resistant cultivars

Some plants are sold as resistant to pests, for example, lettuce selections resistant to root aphid.

Diseases

Often this is more about limiting disease spread rather than eradicating it completely.

Be vigilant

Try and spot early signs of disease so that you can take action before it spreads more widely.

Grow and maintain plants in a way that makes disease less likely

Examples include ample spacing of pot plants in a greenhouse to help prevent outbreaks of botrytis (grey mould). Pruning trees and shrubs to give an open structure will result in better air circulation and reduce the risk from diseases such as leaf spots, rusts and scabs. Accurate pruning at the branch collar will avoid a pruning stub then dying back, which can be a common entry point for coral spot and some canker pathogens.

Remove diseased sections of plants

By cutting out disease, you may limit the spread. Coral spot is an example where a fungus from infected tissue can grow down into healthy wood. With soil-borne diseases, such as honey fungus, remove infected roots when digging out plants.

Remove other diseased material

Break the cycle of reinfection at the end of the season by clearing up infected leaves or fruit. For example, rose leaves infected by rose black spot or apples with brown rot can carry spores from one year to the next. However, if there's no evidence of disease then there is no need to be too scrupulous about clearing away old leaves and other dead plant material, as this can provide a habitat for wildlife and increase the biodiversity in your garden.

Add organic matter

If used as a barrier, mulch can stop disease spores splashing back onto plants. As an alternative to clearing up fallen rose leaves a thick winter mulch will bury any leaves affected by rose black spot and stop spores from them re-infecting new spring growth.

Incorporating organic matter such as green manures into soils can sometimes help to combat soil-borne pathogens, as competitive micro-organisms are created in the decomposition process. The act of cultivating the soil in itself will break up small roots exposing pathogens to the environment.

Crop rotation and laying areas fallow

Rotating crops on your veg plot will prevent reinfection of vegetables of the same family by starving out soil-borne diseases (as well as provide better nutrition and healthier plants). Rotation tends to work best against diseases with a narrow host range, such as Fusarium wilts. For some problems with a wider host range areas may need to be left fallow for several years.

Crop rotation can also help to minimise issues caused by soil-borne nematodes (e.g. potato cyst nematodes) and some of the insects that spend at least part of their life-cycle in the soil (e.g. as pupae). For those invertebrates that also spend part of their life-cycle above ground (e.g. allium leaf miner, beet leaf miner) crop rotation needs to be used in conjunction with a physical barrier such as an insect-proof mesh.

Resistant cultivars or rootstocks

Resistance is not the same as immunity, but it can often allow a crop to be harvested before disease takes its toll.

Resistance in edible crops is especially important as UK home gardeners have very few fungicides available, even if they wished to use them. For diseases such as potato blight and tomato blight (caused by the same pathogen) the use of resistant cultivars is an important and effective management technique.

Some forms of organic gardening permit a limited number of controls that are derived from animal or plant materials. Your own personal viewpoint may or may not permit these.

Organic controls

Insecticides derived from natural products may have less impact and persistence in the environment than purely synthetic chemicals. Pyrethrins are an example of this, however they are still chemicals which poison the organisms with which they come into contact.

Oils and soaps

Other natural products are based on vegetable oils, animal oils and soaps. These are classed as surfactants. They act by smothering rather than poisoning pests. They may also kill non-target species such as beneficial insects.

Biofumigants

In some cases plant-based remedies are the only control option. For example, chemical soil sterilants are no longer available. Instead, mildly toxic compounds released by certain brassica crops, such as mustard 'Caliente' are worked into the soil. These biofumigant materials can reduce some soil pests such as nematodes. They are thought to have negligible adverse environmental impact.

In greenhouses, a garlic fumigant is available as a pest disperser.

Home brews

Some people turn to home-made brews as they try to reduce chemical inputs into their gardens. These apparently benign concoctions containing essential oils, washing up liquid or similar are best avoided as they may pollute the wider environment or harm plants, for example by scorch. They can harm a range of organisms and as they are not properly tested, we can't be sure of their environmental effects.

Whatever their origin, these products kill components of biodiversity, so should be used with discretion.