Aphids. If you have been gardening for any amount of time you have probably seen them. Fortunately, while unsightly, they are not as much of a concern to the health of your plants as many other pests. In most cases, they will not actually cause any damage to the health of your plants. Because of this treating the plant for its own health is often unnecessary.
What are aphids?
Aphids are small pear shaped insects. They are typically green, but can also be red, brown, black or yellow. They are often seen in clusters almost completely covering a part of a plant. For example, they particularly seem to love rose buds.
There are all sorts of different kinds of aphids, some of which only feed on a particular plant. This is why they can vary in color so much. Fortunately, identifying the specific species is unnecessary, and they all look similarly enough to easily be recognized as aphids. University of Minnesota has excellent pictures of several aphid species.
Aphids have interesting life cycle and reproduction habits.
Their physical characteristics and reproductive habits are based on the season and availability of food. During the warm weather months, female aphids give birth to live young. They do not require males to reproduce. During this time, they can also give rise to winged aphids. They will do this if the food source diminishes or they get over crowded in a given location. The winged aphids can then sail on the wind to other plants.
As the weather cools in the fall, males are produced as part of their survival strategy. These males mate with the females so that the females can lay eggs. Females lay eggs on the plants prior to winter setting in. These eggs overwinter and give rise to the new generation of aphids in the spring. As the weather warms, the eggs hatch producing a new generation of female aphids that will give birth to live young all summer.
How do I recognize aphids in my garden?
Aphids are easy to recognize if they are present in large numbers. You will see tons of little often translucent looking little pear shaped insects all over the leaves or stems of your plants. If they have been there for a while, you will likely also see white ‘dust’ all over the leaves. Sometimes you might notice this prior to seeing the actual aphids. This white ‘dust’ is shed aphid exoskeletons.
Mature aphids, smaller nymphs, and exoskeletons can be seen in this picture of aphids on a January cabbage.
You will notice there are clusters of exoskeletons in areas that currently have no aphids, and clusters of aphids in areas without exoskeletons. They fed on the exoskeleton area then moved on to a younger more tasty leaf. These aphids are feeding on the plant’s sap using slender sucking mouth parts. They like to congregate on new tender growth that is delicate and succulent.
You don’t typically see any aphid damage symptoms on the plant aside from the insects themselves being present. However, if the infestation is bad enough, you might. These symptoms might include twisted leaves, stunted growth, or yellow foliage.
Why do the leaves look wet, and what is this black stuff?
Another symptom of aphid feeding you might see is honeydew and sooty mold. Honeydew is the waste secretion of the aphids. It can look like sticky or wet spots on the surfaces of plant leaves. Honeydew in and of itself is not harmful to the plant. However, it can create a sticky mess if it drips down on anything that is underneath the plant. It can also result in the unsightly growth of sooty mold.
Sooty mold, like honeydew, is not harmful in and of itself. It is very unsightly though. It can cause your plant and anything under and around it where honeydew has dripped to turn an ugly black color. Though they are unsightly, neither sooty mold or honeydew require any treatment. Rather, if you have a problem with sooty mold or honeydew it is important to control the plant pest causing the honeydew secretions. If you control the plant pest, the unsightly sooty mold and honeydew will resolve themselves.
What can I do about the aphids?
As we said before, in many cases treating your plants for aphids is unnecessary. If they are present in low numbers and are not doing any obvious harm to the plants we would recommend monitoring them rather than treating them.
Why you might ask? Aphids have a lot of natural predators in the landscape. Often though you might not see them or realize it. These predators are keeping your aphid population under control. If you spray for aphids and unintentionally kill off your beneficial insects, you risk having an explosion of aphids or other pests like spider mites. These outbreaks are often seen within a week of spraying. It is usually better to let Mother Nature self regulate. Additionally, if you think you need more control than the beneficial insects present seem to be managing there are a variety of predatory insects such as ladybugs available for purchase.
It is a good idea to remove weeds from in and around your garden as they can sometimes harbor massive aphid populations. You can also blast aphid covered plants with a strong spray from a garden hose. This will knock the aphids off, and can also help wash off the unsightly sooty mold that might be present. However unlike pesticides, it will not have a detrimental effect on the beneficial insects present. Unlike the aphids you wash off, any beneficial insects knocked off can fly back onto the plant to resume aphid eating.
Indoor plants will probably need more help
Unfortunately, if you are growing plants indoors in a controlled environment, you will likely have to take aphid control into your own hands. Most houses and greenhouses do not have a population of predatory insects present to control pest outbreaks.
Fortunately, aphids are fairly easy to control. A mild pesticide such as Neem Oil or Insecticidal Soap is usually sufficient to control them. These insecticides are relatively harmless to most beneficial insects and humans. They are contact insecticides so the aphids need to be exposed to them to be killed. For this reason, the plants will need to be sprayed thoroughly. Be sure to get the undersides of all the leaves. Repeat applications can be made until the aphids have been eliminated. These mild pesticides will likely also be sufficient if you need to reduce the aphid population on an outdoor plant.
If you do decide to use a more toxic pesticide then this, please be sure to read the label carefully, and use it responsibly. Many of these pesticides can make aphid outbreaks worse by killing off beneficial insects. They are also extremely toxic to pollinators, so do not spray them on flowering plants, or plants that will be flowering soon. As always, if you are unsure, it is best to talk to a local extension agent or pest control company for guidance.
We hope this helps you take control of your next aphid outbreak!
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