Controlling Aphids in the garden

Aphids are the irritating insects commonly buzzing in our ears at night or getting in our mouths as we talk. These small sap-sucking insects are very common and very troublesome. There are over 4,000 different species of aphid, 250 which are pests. They originated around 280 million years ago, and scientists have yet to pinpoint their country of origin. Aphids breed rapidly and can harm plants or crops; however, they pose little danger to humans although they are a nuisance. There are a few reports of aphids biting humans but that is exceedingly rare.

What Do They Look Like?

All aphids are soft bodied with a round abdomen and small head. They are between 1/16” and 1/8” long. Depending on the sub-species, they can be black, green, white, orange, or blue-green. The two most common colours are green and black. They have two compound eyes and tube-like mouthparts. Adult aphids are usually wingless but will develop wings due to environmental conditions. When there are too many aphids in a given area, they gain wings that allow them to migrate to other plants.

Where Do They Live?

Aphids are found in a myriad of climates throughout North America. They live in the cold areas of Canada and the warm coastlines of the United States, to the consternation of many people. They survive the cold months by laying eggs that hatch in spring. Aphids will inhabit many different plants, often on the underside of leaves. They sample the sap to determine if the plant is worth inhabiting. Once they find a suitable plant, based on its sap, they will infest it. Different varieties of aphid are attracted to different plants. These aphids are often named after the plants they favour such as: potato aphids, green peach aphids, melon aphids etc.  

Exclusive Diets

Aphids will only feed on one type of plant at a time. They will choose their new host and feed exclusively on its sap. They first pierce the plant with their tube-like mouths. They feed on the sap through phloem and xylem vessels. These vessels are found throughout the leaves, branches, stem, and roots of a plant. Simply put, phloem vessels send sugars and proteins from the leaves to the roots while xylem vessels send nutrients from the roots and soil to the stems and leaves. The phloem sap is easier to eat as pressure sends it directly in the aphid’s mouth. It also has a higher concentration of sugar and amino acids. Xylem sap, on the other hand, requires active sucking. Despite the ease of obtaining phloem sap, aphids are frequently found to be drinking xylem sap.  

Lifespan and Development

Aphids live for about a month. They reach sexual maturity in four to ten days. They develop through the standard insect phases: egg, nymph, adult Aphids are able to reproduce while still in the nymph stage nymphs. Most aphids reproduce sexually but some aphids can reproduce asexually and sometimes bear live young instead of eggs. In colder climates, eggs are laid before winter and remain dormant until the following spring. In warm climates, aphids reproduce year-round.

Chemical Treatments

The chemical treatment of aphids is difficult due to their rapid breeding and the inefficiencies of spraying insecticide. Insecticides work when they touch the insect. Many times, these sprays miss the understand of leaves and other areas aphids inhabit. Thus, many aphids avoid it. Aphids are also resistant to some insecticides. If one is used, it should be a biological insecticide that attacks resistant aphids.

When chemical treatments are used, an insecticide soap or oil is the best choice. The oils are often petroleum-based or plant-based. They smother aphids and require saturating the plant. They should be mixed well with water and sprayed on the underside of leaves. Most of these treatments do not kill beneficial insects.

Non-chemical Treatments 

Non-chemical treatments are preferred to control earwigs because they do not harm the environment or beneficial insects. They are also more effective in many cases. Non-chemical remedies include high-powered washing, natural enemies, and plant-based treatments.

Water Based Treatments

One effective method for removing aphids is spraying plants with a high-powered hose. The water will remove all aphids, if done carefully. A special wand is needed that provides a powerful, yet plant-safe stream. A regular hose head may damage the plants and may not reach the underside where most aphids live. A wand designed for mites is angled 90 degrees and will easily reach the underside of leaves.

Another water-based remedy is to place a medium, yellow container of water in the affected area. The container must be filled to the top. The yellow colour attracts the aphids, and the water will trap them when they land on it. Water alone can be used but a mixture of dish soap, vegetable oil, and water will ensure that they can’t escape the container. The ideal mixture is 2.5 tsp dish soap, 2.5 tsp vegetable oil and 1 gallon warm water. This can also be sprayed on plants.

Natural Enemies

Ladybugs are small but voracious predators. They consume large quantities of smaller bugs like aphids. They are sometimes called the gardener’s best friend because they eat many different kinds of small pests. There are two ways to use ladybugs to remove aphids. The first is to attract ladybugs to your garden. The second is to buy and release ladybugs. While releasing the ladybugs may seem best, studies have shown that most of the ladybugs will not stay where they are placed. This can be mitigated to some degree by placing water nearby and releasing them in the early evening or at dusk. Nonetheless, it can be difficult. To attract ladybugs to your garden (or keep the captive ones around), you can place certain plants in the garden. Ladybugs are attracted to mint, fennel, dill, yarrow, and dandelions.

The less savory enemy of aphids is the parasitoid wasp. Two types of wasp will attack aphids: aphidius colemani and Aphidius ervi. The wasps will sting the aphid eggs and inject its own larva into the egg. When it hatches, the wasp larva slowly feed off of the aphid larva. A female wasp can inject hundreds of eggs, eliminating many young aphids. Only certain types of wasps are approved for use in North America and even their use may have unintended consequences on the ecosystem. Before using natural enemies, contact your local government or agricultural center.

Natural Remedies

The main natural remedy used against aphids is diatomaceous earth.  Diatomaceous earth is made from the fossilized remains of tiny aquatic organisms. The skeletons are made up of silica, which is basically hard rock and crystals. It is not poisonous; its sharp edges cause insects to dry out and die. It can be spread on or around plants to prevent unwanted insects. However, it can kill beneficial insects such as bees and should be used carefully.

Certain plants can also help repel aphids when they are placed in close proximity. Garlic and chives are beneficial when placed near lettuce, peas, and rosebushes.

Prevention

The two main tips for preventing aphids involve pruning and watering. Aphids are attracted to plants with high nitrogen levels. Over-watering or the over-use of fertilizer can cause plants to have high nitrogen levels. Using slower acting fertilizers and avoiding over-watering can prevent this. Careful pruning can also make plants less hospitable to aphids. First, you can prune off heavily infested leaves or plant parts. More importantly, make sure the leaves don’t touch the ground. This prevents ants from infesting the plants. Many aphids have symbiotic relationship with ants. The ants provide protection while the aphids provide them with honeydew. Preventing ants will in some cases prevent aphids. Sticky tape around the trunk can also keep ants away.

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