Aphids on Plants: Their Damage and How to Eliminate Them

Adults and nymphs eat plant juices, leaving behind misshapen, yellowing, curling or stunted leaves. Most aphids prefer new growth, but some species like green peach aphids feed on various plants. You will also see aphids on roses. Other species like the rosy apple aphids feed on only one or a few plant varieties.

Aphids are usually found on the undersides of leaves. If you found a sticky substance on the stems or leaves, it is a sign that your plants are infested with aphids. This substance is called honeydew. Aphids secrete honeydew when they feed on plants and this substance can attract ants and other insects that gather the liquid for food.

The honeydew can drop onto your driveway, car or outdoor furniture and encourage sooty mould growth, a fungal disease that causes leaves and branches to turn black. Galls may also form on leaves or roots due to the feeding habits of aphids.

Spray infested plants with a strong stream of water from a hose. You can also use a cotton swab to knock them off your plants. This method works best for light aphid infestations. You can also dip the plants in room-temperature water. This method is ideal for plants with delicate foliage. You can also remove heavily infested parts and throw them outside.

You can make a DIY insect spray by mixing cayenne pepper (one teaspoon), one garlic bulb and one small onion in a blender or food processor. Add the paste to one quart of water then steep for one hour. Strain the mixture with cheesecloth then adds one tablespoon of dish soap. You can store the mixture in the fridge for a week.

Neem oil has fungicidal and insecticidal properties that can kill aphids. According to the EPA, neem oil is safe to use on food plants, ornamentals, and vegetables.

You can buy insecticidal soaps or make your own. If you want to make one, you only need to mix one teaspoon of dish detergent with one gallon of water. Transfer the mixture into a spray bottle and use it on infested plants. If you want to buy one, choose a product that has no additives or perfumes that can damage plants.

For insecticidal soaps, we recommend the use of Safers Insecticidal Soap RTU 1L, Safers 3-In-1 Spray RTU 1L, and Safers Defender 1L RTU.

Chemical sprays should be used as a last resort or when the infestation is too severe that you have no other choice, but to use such products. Treat the infested plant with chemical sprays that contain pyrethroids, pyrethrins or imidacloprid. Pyrethrin-based chemical sprays have low toxicity, so they are the safest product to use.

For chemical sprays, you can use Ortho Bug B Gon Eco Insecticidal Soap RTU 1L or the Safers End-All II 1 L RTU C7.

Diatomaceous earth (DE) can kill aphids, but it will not harm plants. However, it is harmful to butterfly larvae and bees, so consider covering your plants with netting to prevent these beneficial insects from feeding on treated plants. A product we recommend is:

Aphids have natural predators such as the soldier beetles, lady beetles, brown and green lacewings, blister beetles, hoverflies, damsel bugs and big-eyed bugs. Both nymphs and adults usually eat aphids. Parasitic wasps or parasitoids that eat aphids include braconid wasps and ichneumon.