Organic pest management of aphids

Green peach aphids on a cabbage leaf with brown-colored “mummies” showing proof of parasitism by tiny stingless wasps.

Description

The following tools and techniques are meant to provide some examples of organic pest management (IPM) tactics for various species of aphids using the Four T method. For the purpose of this sample, green peach aphids (Myzus persicae) are the target shown.

Target

Our target is the adult aphid who is reproductive ready, but any age and/or size of aphid will do. Any aphid should be a target. Green peach aphids (Myzus persicae) are tiny, green aphids that hang out under leaves, flower buds, flowers, and soft plant stems.

Timing

General calendar time: Outdoors. The winged forms of adult aphids emerge anytime during mid to late spring. They may be present all year long in greenhouses or other indoor growing situations.

Degree days: n/a 

Aphids have the unique ability to give live birth during the growing season without mating. Adult aphids observed on plants during the bulk of the growing season are females with the ability to clone themselves.

There is less of a need to use the degree day formula for aphids. The time to respond is when they are observed…and this can be any time from mid- to late May. This in mind, it is important to know what aphids look like, to scout often, and be aware that their presence can increase very quickly if they are allowed to reproduce….especially during periods of warm weather.

Tool(s)

Tool #1: Syringing (Type: Mechanical/Water pressure)

Syringing is a fancy word for spraying aphids off your plants. Syringing is not the most effective approach, but it may provide some efficiency during an outbreak. For small operations, syringing is a kind of first responder-type of response; the effectiveness of syringing largely depends on the type of crop and the amount of time a grower has to spend removing aphids from plants.

Techniques for tool #1: Syringing

  1. Spray your plants using enough pressure that knocks aphids loose without damaging plants.
  2. Syringing works well with potted plants and mature seedlings that you can tilt or place on their side so that you can remove aphids without them landing in the soil of the potted plant, where they can find their way back to the main stem and re-infest the plant.
  3. Repeat technique every day or every other day to prevent aphid infestations from rebounding.

Tool #2: Crush aphids with your bare hands (Type: Physical)

Yes, aphids are easy to crush. But for this tool to work, you need to observe the following:

  1. Scout often. Detecting early infestations is critical for detecting and preventing outbreaks. You can thwart early small aphid infestations from developing into outbreaks by crushing small infestations before they spread. A small amount of pressure will crush their small soft bodies. It sounds cruel. But aphid infestations have a way of building slowly and gradually. If you don’t manage small infestations, their ability to reproduce quickly and can lead to your crop being overwhelmed.
  2. Check under leaves toward the top of the plant first. Be sure to check lower leaves as well.
  3. Check for aphids on new leaves and young buds where the concentration of nitrogen is high.
  4. Check for aphids – especially after fertilizing.
  5. Check for signs of parasitized aphids. Parasitized aphids show up as mummies. Aphid mummies mean that parasitic wasps are present in your growing area; these tiny stingless wasps kill aphids by laying their eggs inside of them.

Tool #3: Spray insecticidal soap (Type: Chemical)

Insecticidal soap works well against aphids because of their soft bodies.

Insecticidal soap is not a poison or a nerve toxin…it is a formulation of soap that is designed to be gentle enough to use on most plants.

The “insecticidal” part of insecticidal soap comes from its mode of action. The active ingredient of insecticidal soap – the potassium salts of fatty acids – work to dissolve aphids’ bodies that causes them to dry out from loss of moisture.

Tool #4: Release beneficial insects (Type: Biological)

You do not want to use just any beneficial insect. You want an insect that will actually consume aphids on the plants in your growing area.

  1. Ladybeetles (predator). Releasing ladybeetles for aphids might “sound nice”, but chances are that the adults will fly away. Better to add a female and male within a sleeve so they lay eggs that will hatch into aphid-eating larvae.
  2. Lacewings (predator). Better to release green lacewing eggs that will hatch sooner into legged (not winged) larvae that feed on aphids as well as other small insects, like thrips and the eggs of other plant-feeding insects, such as Colorado potato beetle.
  3. Predaceous midge larvae (predator). Aphidoletes aphidimyza are not only fun to say, they are very effective at seeking out low levels of aphid infestations and laying eggs that will hatch into very effective aphid predators. 
  4. Parasitic wasps. Aphidius colemani are kind of like the air force. They are mobile, can seek out aphid infestations, and you can observe the effects of their parasitic behavior on aphid infestations when you see their mummies.

 

Cabbage leaf with green aphids and brown/tan aphid mummies
Aphid “mummies”
Tool #5: Plant cup plants and goldenrod near your growing area (cultural)

Cup plants and goldenrod can attract a specific species of red-colored aphid that is specific to cup plants and does not move to other food plants. These red-colored aphids attract a wide range of beneficial insects without moving to other plants.

Photos of red macrosiphum aphids on cup plants with beneficial insects.

Resources

University of Minnesota Extension

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