How to manage pest attacks in your garden

The Turnera plant attracts insects like ladybirds, which are pests’ natural enemies. Photos: Assoc Prof Dr Norida Mazlan

The first step in pest control is to identify the pest, as not all insects you see in your garden are harmful. Most common insect pests damage plants by chewing or sucking the leaf cellular fluid sap, which causes discolouration.

Some insects also transmit viruses.

Aphids, whiteflies and Solenopsis mealybugs are common pests that damage plants by feeding on plant sap and transmitting viruses.

Aphids cause plants to become puckered, yellow and stunted, while whiteflies affect young plants more severely, causing leaf curl and mould growth.

Whiteflies can be found on the underside of plant leaves, resembling white powder, and will take flight when disturbed.

Solenopsis mealybugs specifically target okra plants, reducing their quality by secreting a sticky substance (called honeydew) and spreading diseases.

Pest control often involves a combination of methods.

Controlling insect pests can be done through their natural enemies, such as ladybirds and dragonflies. To introduce these insects in your garden, plant various nectar-producing plants like Turnera, cosmos (ulam raja) and sunflowers that will attract these beneficial insects.

A plant covered with white powder and leaf curling are symptoms of whitefly attacks.

Natural pesticides, including biopesticides, are a good alternative to synthetic pesticides because they have a lower negative impact on humans, beneficial insects and the environment.

They repel pests through unpleasant odours, tastes and touch. Pests can even recognise these repellents from a distance, preventing them from attacking, biting, flying, or landing on plants.

Common natural repellents include neem and a combination of garlic, chilli and ginger solution.

Neem (Azadirachta indica) contains the active ingredient azadirachtin and is effective against most pests (in particular against insects in the Lepidoptera and Hemiptera family), repelling them by disrupting their feeding and growth.

Neem exerts antifeeding properties, where it prevents insects feeding on the leaves by creating a vomiting sensation in them. Additionally, neem also hinders female insects from laying their eggs.

Neem biopesticide can be prepared by shredding 1kg of neem leaves, then mixing them with 5l of water (best is rainwater). Seal the mixture in an airtight container, and store in a dark room for at least 24 hours, during which bubbles and a strong pungent smell will be released.

After fermentation, sieve the solution, then add 50ml of the solution into one litre of water before spraying onto plants.

A combination of garlic, chilli and ginger is an effective natural repellent.

Garlic (Allium sativum) repels insects like caterpillars, whiteflies and borers due to its strong odour. The active ingredients in garlic, such as allicin and flavonoids, can interfere with the development of cell membranes in parasites, bacteria and larvae.

Chilli (Capsicum frutescens) contains capsaicin, which produces a “hot” sensation that repels chewing pests like grasshoppers and caterpillars and disrupts their insect physiology.

Ginger (Zingiber officinale), with its active ingredients zingerone and polyphenol compounds, exhibits antioxidant properties and repels pests by generating a warming sensation that raises insects’ body temperatures. It also hinders insect growth and acts as an antifeedant.

To create a solution of garlic, chilli and ginger, combine and blend one garlic clove, six bird’s eye chilli, and a 2cm piece of ginger with 500ml of water.

Strain the mixture, transfer it to a bottle, and let it sit at room temperature for at least 24 hours, after which the solution can be stored in the refrigerator.

Before using the mixture, dilute it with a 1:10 ratio of solution to water and add one teaspoon of dishwashing detergent and one teaspoon of cooking oil. Be cautious, as this concoction may harm plants if misused. Test it on a small section of the plant before applying it to the entire plant.

For optimal results with biopesticides, apply them directly onto areas where pests are present, such as under the leaves. Applying biopesticides in the evening is also more effective than in the morning. The application frequency should be once every four days, though this may vary based on the severity of the infestation.

Other pest control solutions are coloured sticky traps and diatomaceous earth (DE), which can be purchased online. Hang the sticky traps above or between plant canopies to effectively catch insects. Yellow traps work well for insects, while blue traps target thrips.

Apply DE as a powder, sprinkling it around plants to deter snails and slugs, or on leaves to eliminate other pests.

However, DE is only effective in dry conditions and must be reapplied after rain or watering plants. Snails and slugs can also be repelled using burnt egg or cockle shell powder.

Assoc Prof Dr Norida Mazlan has 20 years of experience in plant protection. She also heads the Dept of Plant Protection, Faculty of Agriculture, Universiti Putra Malaysia.