Suppress and Eradicate Garden Pests Sustainably

There are many ways to suppress and eradicate garden pests sustainably if you find you can’t prevent them invading your garden. Such approaches mostly involve some observation of your garden to identify which pests should be targeted, planning which or how many techniques to use and reducing chemical use.

Manual Removal

When you notice pests, it is sometimes quickest and most efficient to remove them by hand.

Picking Off/Fly Swat

Since some caterpillars can sting, use a gloved hand, squash and/or remove them.  They can be disposed of by squashing them into the ground or feeding the to chickens.

Water Jet – Hose

Many pests, like aphids and peach and pear cherry slug, can be hosed off plants. Aphids cannot/will not return to the plant.  However, bear in mind that this is probably not the best use of water in a country prone to droughts.

Pruning

If there seems to be no other option, prune out infested plant parts e.g. this is the effective for citrus gallwasp. Dispose of diseased or infested material in plastic bags (sealed) in rubbish bin or burn them.

Barriers and Traps

For certain pests that you have noticed in the garden, you can avoid removing them by installing barriers or traps.

Copper Tape

This is effective in preventing attack by snails and slugs.  Its appears to repel snails/slugs because a mild electrical charge occurs when they cross/touch the tape. Tape should be at least 5cm wide and needs to be shiny and clean since tarnished tape will not work. It is most effective when placed on the surface of pots or benches as long as you are sure that there are no snails/slugs inside the area you are enclosing. This method can be used for individual plants in the ground, but the tape needs to be at least 10cm wide with half buried below the soil surface.

Netting

If birds, possums, bats or rats attack your plants or fruit, netting individual plants, branches, fruit clusters or whole plant beds is an effective approach. For whole garden beds or large trees use 5mm x 5mm (or smaller) netting pulled taut over a frame/structure over plants. For small trees, single branches or fruit clusters, netting can just be in the form of a bag.

Regulations under the Prevention of Cruelty to Animals Regulations 2019, effective since September 2021, state that netting sold or used must have a mesh size of 5mm x 5mm or less at full stretch. Larger mesh sizes trap birds and bats ultimately killing them.

Horticultural Glue

This can be applied in bands around the trunk of trees/plants at an appropriate time to prevent the migration of insects such as ants which feed on honeydew and spread sooty mould.  It can also prevent larvae of codling moth or elm leaf beetle moving up into the canopy where they complete their life cycle. Layer a band of glue all the way around the trunk/base of tree and replace as necessary.

Corrugated Cardboard

When wrapped around the trunk of trees  e.g. apple trees, it can address codling moth infection of fruit since the moths use the dark corrugated spaces to pupate. The cardboard needs to be secured with tape or string. By periodically removing and destroying the cardboard the moths can be prevented them from completing their life cycle.

Dry/Powder Barriers

A number of dry materials on the soil surface around plants can deter slugs/snails. Examples are coffee grounds, diatomaceous, sawdust, lime or copper sulphate. These substances need to be kept dry and should be used in thick layers and replaced when damp or depleted.  This means frequent reapplication or protection from rain or sprinkler irrigation.

Traps

Sticky Insect Traps

These traps use colour to attract insects – yellow strips for aphids and whitefly and blue for thrips and leaf miner.  They contain an extremely sticky glue that prevents insect escape.  Unfortunately, they will trap both pest insects and those that are  desirable. Hang in locations with problem pests. Monitor and replace when necessary.

Snail/Slug (Gastropod) Traps

These can be made from pieces of cardboard, wood or plastic board and even just a flowerpot.  Place on ground in a damp spot in garden.  If you lift them after 1 or 2 days lift you can remove any snails/slugs congregated underneath.

Another type can be made from a glass or plastic container sunk in the ground or from a commercial version with the top level with the soil surface. Add beer or sweet liquid. Snails/slugs are attracted to the sweetness and will drown when they enter.  These traps need to be cleaned out regularly and preferably have a cover to protect from rain or sprinkler irrigation. However, they are non-specific and could potentially kill non-target organisms.

Bug Zappers

These traps are devices that attract flying insects when lit up via a 240 volt power point and electrocute them on a high voltage conducting grid.

Their disadvantages are that they do not discriminate between pest and beneficial insects and can generate airborne particles from the insects as they are electrocuted. These particles can be potential allergens and possibly contaminate food. They could also spread viruses and bacteria into air which could be inhaled by people nearby. They should be located way from areas where food is prepared or consumed.

Repellents and Attractants

Companion Planting

Particular plants can be used to attract, repel or enhance health of valued plants such as fruit and vegetables.  For example, land cress Barbarea verna effectively attracts the diamond back moth and large cabbage moth which then lay their eggs on it.  It contains a chemical which poisons the moth larvae after they hatch and eat the leaves. Click here for an overview of companion plants for fruits and vegetables.

Visual Bird Deterrents

These are designed to scare birds away.  They may be made from reflective/shiny material such as lights, mirrors, reflectors, reflective tape, or can be materials hung in trees so that they move with air movement e.g. flags, rags or streamers.  They can also look like enemies such as dogs, humans (a scarecrow) or birds of prey e.g.hawks.  These are only effective for short periods of time since birds quickly habituate to them and will resume normal activities.  They should be changed when no longer effective.

Pheromone Lures

Chemicals in these lures are the artificial pheromones that male or female insects emit to attract those of the opposite sex for mating.  These lures cause insects to become confused and to aggregate, thereby  decreasing their opportunities to mate. This means that their reproductive rate declines leading to reduction in population sizes. Such lures only work on mature or adult stage insect pests. You will need to monitor pest type and number and replace lures or clean them periodically if necessary.

Reduce Use of Chemical Pesticides

Chemicals used in pesticides are one of the causes of observed global declines in insect populations . While only some of the above control methods are not specific for pest insects, spraying with chemicals is mostly unspecific and can actually increase pest problems by killing beneficials too. Populations of beneficial insects frequently take longer to recover than pest insects so pest rebound occurs faster since there are fewer of their enemies.

Most chemical pesticides have extremely negative impacts on species beyond the insects targeted. This includes birds, frogs, pets and humans.  Bee populations are badly affected by a range of chemical pesticide ingredients including neonicatinoids.  Migration of songbirds and resulting decreases in mating success are also affected by neonicatinoids.

Furthermore, pesticide chemicals can spread beyond sites sprayed since some are absorbed by plants and then transferred to other species which eat them and many can be washed off by rain and then move through soil into waterways where they may affect fish and other aquatic species.

We are very grateful to Bridey Oliver for the research and first draft of this article and to financial support from the Lord Mayor’s Charitable Foundation.