There are over 900 thousand known insect species on earth, but aphid species are some of the most well known to gardeners. Did you know there are many different species of this notorious pest insect? Although we generally refer to all aphids as a general pest, different species actually affect gardens in various places because they have specific winter hosts.
Aphids live what’s called a holocyclic life cycle, utilizing different plant hosts in summer and winter. Aphid females reproduce asexually during the summer months, giving birth to live female aphids genetically identical to themselves. Aphid populations grow so quickly, because the majority of female aphids are actually born pregnant! When fall comes, female aphids also begin to give birth to males. At this time of year, male and female aphids mate, producing eggs that will overwinter on woody host species specific to the aphid species.
When the weather begins to warm in the spring, aphids emerge from eggs, feed first on their woody winter host plant, and then move to their herbaceous summer hosts – often your vegetable or flower garden. Have you ever noticed that some aphids have wings and others don’t? In order to move to a new host, some aphids actually undergo a hormonal change based on their environment that allows them to grow wings. This happens when host plants become too crowded, a poor food source, or when it’s time to switch from winter to summer hosts. The good news is, aphids are actually poor flyers. They can barely see, and don’t know if they’ve landed on something edible until they actually taste it!
So, what makes aphids a pest, why are they attracted to your garden, and how can you manage them?
Why are Aphids Considered Pests?
Aphids are considered garden pests because of the context in which gardeners interact with them. Of the hundreds of thousands of known insect species, many don’t affect gardeners, some are labeled as beneficial because they support gardening activities, and others, like aphids, are considered pests. Pest insects are those that cause problems for people. These “bad guys” are destructive to something we as gardeners care about, our flowers and vegetables. Because of this, we consider them pests.
Aphids are phloem feeding insects. This means they use piercing-sucking mouth parts to tap into the phloem of plants, extracting all the sweet sugars and other metabolic products produced by plants via photosynthesis in the leaves on their way down to the root system. Although this causes little tissue damage (unless an infestation is very severe), it robs the effected plant of nutrients and energy. Aphids can also carry plant diseases and viruses, which they transmit during feeding. Finally, aphid feeding results in honeydew production. Sugary, sticky honeydew on plant surfaces can create an ideal environment for black sooty mold growth. Although aphids themselves can reduce plant vigor and growth, the secondary problems that can result from their presence can also be detrimental to the garden.
Greenhouses are amazing because they create a protected, indoor environment that allows you to grow food and flowers year-round. However, greenhouses also create a protected environment for insects, sheltering them from natural population controls including wind, heavy precipitation and temperature swings. Because of this, aphids can become very pesky in greenhouse environments if not monitored and managed well.
What Attracts Aphids to your Garden?
Aphid feeding in your garden is biologically driven, but certain conditions may cause aphids that do end up in your garden to stay, reproduce and cause damage. Keeping plants in your garden healthy is actually one of the best ways to prevent aphid outbreaks and. Here are a few things you can do to avoid stressed plants and aphid overpopulation:
- Maintain nutrient-rich, well structured soil.
- Develop and follow a watering or irrigation scheme that consistently delivers adequate moisture to plants.
- Maintain proper plant spacing, avoiding overcrowding and thin when necessary.
- Ensure adequate airflow (critical for aphid control in a greenhouse environment).
- Avoid stressing plants by exposing them to temperature extremes.
- Provide additional nutrients in the form of organic fertilizers only when necessary, especially avoiding too much Nitrogen fertilizer, which stimulates the tender vegetative growth that aphids are most attracted to.
- Select plant varieties that are resistant to aphid infestations and/or the plant diseases they transmit.
- Rotate plant varieties during different growing seasons and use succession planting techniques.
- Maintain proper garden sanitation.
- Ensuring your garden is well weeded and that weeds are minimized in the surrounding landscape.
Assessing the Situation
Once you’ve noticed aphids on your plants, like we did in our 15′ Growing Dome at Growing Spaces, you have to decide whether some kind of pest management is warranted based both on personal tolerance and plant health concerns. Generally speaking, gardeners hit their “aphid tolerance threshold” that dictates management prior to the point at which plant health becomes a major concern. These insects just bother us, and that we want to reduce their numbers.
At Growing Spaces, different team members have varied tolerances for aphid presence, but we generally remove heavily infested plants from our Growing Domes and use integrated pest management techniques for aphid control otherwise. Really, one of the toughest concepts for many gardeners to come to terms with is that APHIDS ARE PART OF THE GARDEN ECOSYSTEM, and aiming to completely eradicate them is futile. Instead, it’s more productive to consider ways to manage and control aphid populations so they cause the least amount of harm and annoyance.
Aphid Control Techniques
Once you’ve determined that aphids are present in your garden and decided you should take some pest management action, there are a number of techniques you can use for aphid control. Integrated pest management techniques include cultural, mechanical, chemical, and biological controls. Cultural controls will not be listed below, because they are primarily prevention methods used to avoid an aphid problems in the first place. Cultural controls include many methods discussed above in “why are aphids attracted to your garden,” including proper irrigation, crop rotation, nutrient management, plant variety selection and proper plant spacing. Often, the most effective management regimes combine a few techniques the fall into each of these categories.
If you’ve decided to manage the aphid population in your garden, there are many management method choices to consider:
- Squishing the aphids (mechanical) – works best if you have a good amount of time, are feeling vindictive and when aphid populations aren’t extremely dense.
- Spraying aphids off your plants with a strong stream of water (mechanical) – can kill some aphids, but mostly just interrupts their feeding on your plants.
- Shaking aphids off of your plants (mechanical) – interrupts aphid feeding, but doesn’t actually harm them for the most part.
- Removal of heavily infested leaves or whole plants (mechanical, cultural) – physically removes aphids from you garden, decreasing populations and removing plants that have lost vigor and are highly attractive to aphids.
- Planting “decoy” plants to attract aphids away from highly desired plants (cultural) – Planting species like marigolds and calendula may lure aphids away from your prized lettuces and other vegetables.
- Introduction of beneficial insects (biological) – physically introducing beneficial insects to your garden. Lady beetles are the most commonly introduced beneficial insect. Keep in mind it’s important to create habitat for your new beneficial insects so they stick around!
- Encouraging beneficial insects (biological, cultural) – creating an ideal habitat for beneficial insects that already exist in your area so they will reproduce in your garden and help to manage pest insects. One good way to do this is to cultivate plants that attract beneficial insects including lacewings, spiders and lady beetles.
- Organic sprays (chemical) – although “chemical” sounds a little scary, organic sprays actually fall into this category, but are a much better alternative to synthetic chemical sprays. Spray ingredients often include soaps, garlic, neem oil and pepper among others.
Growing Spaces Organic Spray Recipe
Interested in the recipe for the organic spray we used in this video? Here’s how Dana made it:
- Boil 1 gallon water in deep sauce pot
- Add 3 tbsp red pepper flakes to the boiling water, cover and allow to boil for 15-20 minutes
- Turn off burner and let chili flakes sit in the water for 24-36 hours (this allows the capsaicin in the chili to soak into the water – capsaicin, the oil that makes chilis hot, inflicts nervous system damage on soft bodied insects, killing them)
- Strain the chili flakes from the mixture using a mesh pasta strainer or cheese cloth
- Put the chili mixture in a storage container or sprayer
- Add a few drops of Dr. Bronner’s peppermint soap (the fatty acids in some soaps injure soft bodied insects)
You can apply this pepper/soap spray to plants affected by aphids to curb and manage populations. Be very careful to avoid your own eyes when spraying (ouch, hot pepper oil!) and keep in mind that using an organic spray such as this one can also injure beneficial insects. If you’ve seen beneficials around, you may want to avoid using a spray and consider different cultural and mechanical management methods.
Do you have your own organic pest control method? Still have questions about aphids in the garden? Ask a question or let us know what works in your own outdoor garden or greenhouse in the comment section below!