Aphids are very common sap-sucking insects that can cause a lack of plant vigour, distorted growth and often excrete a sticky substance (honeydew) on foliage which allows the growth of sooty moulds. Some aphids transmit plant viruses which can be a problem on strawberries, raspberries, tomatoes, cucumbers, dahlias, tulips, sweet peas and many other plants.
Common name Aphids, greenfly, blackfly, plant lice
Plants affected Most plants are susceptible
Symptoms Poor and distorted growth, sticky honeydew and sooty moulds
Active Spring to late summer on garden plants; all year round indoors
Aphids are sap-sucking true-bugs. They range in size from 1 to 7mm (¼in or less) long. Some aphids are known as greenfly or blackfly, but there are species that are yellow, pink, white or mottled. Some species, like woolly beech aphid and woolly aphid on apple, cover themselves with a fluffy white waxy secretion and can be confused with some scale insects, mealybug or whitefly. Most aphids feed on foliage, stems and flowers but some suck sap from roots.
There are more than 500 aphid species in Britain. Some species only attack one or two plant species, but others attack a wide range of plant hosts. Almost all plants can be affected, including ornamentals, vegetables, fruits, greenhouse plants and houseplants.
It thrives in warm conditions, which is why it is not usually a problem on outdoor plants. Glasshouse whitefly is active all year round on houseplants and in greenhouses.
You may see the following symptoms:
It is usually possible to see aphid infestations with the naked eye, and they tend to colonise shoot tips, flower buds and the underside of younger leaves
Aphids cause stunted growth with curled or distorted leaves. This can weaken the plant
Many aphids also excrete a sticky honeydew which allows the growth of black sooty moulds
White cast skins of aphids can accumulate on the upper surface of leaves
Healthy Plants: Maintain plant health through proper watering, fertilizing, and pruning. Healthy plants are less susceptible to whitefly infestations.
Inspect New Plants: Before bringing new plants into your garden or home, check them for whiteflies and quarantine them if necessary.
Cleanliness: Keep the area around your plants clean. Remove any fallen leaves or debris as these can harbor pests.
Reflective Mulches: In outdoor gardens, using reflective mulches can help deter whiteflies from settling on plants.
Companion Planting: Planting marigolds or nasturtiums near susceptible plants can help deter whiteflies.
Physical Removal: In the early stages of infestation, you can physically remove whiteflies by gently washing them off with water or wiping the leaves with a damp cloth.
Yellow Sticky Traps: These can be used to monitor and reduce whitefly populations. The yellow color attracts whiteflies, and the sticky surface traps them.
Insecticidal Soap or Horticultural Oil: Apply these products according to label instructions. They are effective against whiteflies and are less harmful to beneficial insects.
Neem Oil: Neem oil is a natural insecticide that can help control whiteflies. It disrupts their life cycle and prevents them from feeding and reproducing.
Biological Control: Introduce natural predators like ladybugs, lacewings, or Encarsia formosa (a parasitic wasp) to control whitefly populations.
Chemical Pesticides: If the infestation is severe, chemical pesticides can be used as a last resort. Systemic insecticides are particularly effective against whiteflies. However, be mindful of the impact on beneficial insects and follow the manufacturer's instructions.
Regular Monitoring: Regularly check your plants for early signs of whiteflies, especially on the undersides of leaves.
Avoid Overuse of Nitrogen: High nitrogen levels can attract whiteflies. Use balanced fertilizers to avoid this.
Be Persistent: Whiteflies reproduce quickly, so repeated treatments may be necessary to control an infestation.
Remember, an integrated approach combining several of these methods is often the most effective strategy for preventing and controlling whiteflies.
Ingredients: Mild liquid soap (like dish soap) and water.
Recipe: Mix about 1-2 teaspoons of soap with a liter of water.
Application: Spray the mixture directly onto the aphids and the affected parts of the plant. Be sure to cover the undersides of leaves where aphids often hide. Repeat every few days as needed.
Ingredients: Neem oil and water.
Recipe: Mix a few milliliters of neem oil with a liter of water. Add a little bit of mild liquid soap to help emulsify the oil.
Application: Spray this mixture on the plants. Neem oil is a natural insecticide that disrupts the life cycle of aphids.
Ingredients: Garlic cloves or onions, water.
Recipe: Blend a couple of garlic cloves or one onion with two cups of water. Strain the mixture and use the water.
Application: Spray on the plants. Garlic and onion have natural sulfur compounds that are toxic to aphids.
Ingredients: White vinegar and water.
Recipe: Mix one part vinegar with three parts water.
Application: Spray the solution on the aphids. Vinegar can kill aphids on contact but be cautious as it can also harm plants.
Ingredients: Essential oils (like peppermint, clove, or rosemary), water, and mild soap.
Recipe: Add a few drops of essential oil to a liter of water and a teaspoon of soap.
Application: Spray on affected areas. Essential oils can repel and sometimes kill aphids.
Test First: Always test your homemade spray on a small part of the plant first to ensure it doesn’t cause damage.
Regular Application: You might need to apply the treatment multiple times to control the aphid population effectively.
Thorough Coverage: Ensure to cover all infested areas, especially the undersides of the leaves.
Avoid Strong Sunlight: Apply these sprays during cooler parts of the day or when the plant is not in direct sunlight to prevent leaf burn.
While homemade treatments are generally safer than chemical pesticides, they can still harm certain plants, especially if used excessively or in very strong concentrations. Always observe your plants' reactions after the initial application. If there's any sign of damage, discontinue use.