If you’re a gardener, you’re probably familiar with finding colonies of tiny, gray insects and eggs clinging to the underside of a leaf. If you’re unlucky, you may have even taken a bite of a kale leaf and spat it out quickly. Aphids are a common and persistent pest that lives all over North America.
They’re especially common in households gardens. Since most gardeners don’t have much space to rotate crops and grow mostly the same things year after year, aphid populations can become well established in home gardens. Read on to learn about identifying aphids and treating infestations.
There are a number of species of aphids living all over the world. They are small, between one and three millimeters long, and all varieties share a tear-drop or pear-shaped body. Almost always they are found in colonies and are sometimes so thickly clustered that they look like mold or fungus.
Color variations of aphids can include green, gray, yellow, white, brown, black, or waxy textured. The type of plant the aphids are on is also a clue to identification. Check out these tables of aphid varieties.
At our farm in Washington State, we most commonly see the gray cabbage aphid, which has a waxy, fuzzy, or dusty texture to its colonies. Since all aphids can be managed essentially the same way, specific species identification is not as important as it is with other pests. But keep in mind, aphids aren’t just a problem in Washington State. They’re found throughout most of the United States.
Common Aphid Plant Damage
Aphids drink plant sap, causing wilting, leaf curling, discoloration, galls, reduced production, and in some cases, crop failure. Luckily, an aphid infestation typically will not cause crop failure. They cause the most damage to young and growing crops.
Usually, aphids are just unsightly and unpleasant and make food harder to wash and harder to sell. However, a serious infestation can stunt plant growth and make the product unmarketable.
Aphids prefer juicy green leaves and do their worst damage in the late spring when the weather has warmed up but the landscape and the crops haven’t started to dry out.
During this key growth period for many crops such as soy and canola, even a slight reduction in vigor and growth rate can have an effect on the farmer’s bottom line. This makes these tiny insects a significant pest in certain agricultural regions.
Treating An Aphid Infestation
As with most plant diseases, the best treatment is prevention, and the key to successfully controlling an aphid infestation is catching it early. Always check your crops once a week, not only for aphids but for any pests or signs of disease.
There is no need to be anxious or obsessive about this – missing one or two tiny, plant-colored aphids is not the end of the world. Look for large clusters of bugs and be sure to turn over leaves, as aphids love to hide on the shady undersides.
When you do find aphids, they can be removed manually by spraying them with compressed water out of a hose, pruning or stripping the affected leaves, or by rubbing them off with your fingers.
I once worked at a community garden where the go-to aphid control strategy was to get kids to do “bug checks” and remove the aphids by hand. Since there were kids in the garden all the time, this was actually an effective tactic, but it requires a lot of time and effort if you don’t have a herd of children at your disposal.
There are two other main methods of control – biological and chemical.
Biological Aphid Control
Biological control means introducing natural predators, often called “beneficials.” Lacewings and ladybugs are the most common beneficial insects. They can be ordered online and released.
Always follow the instructions that come with the packaging, as insects can be finicky about the habitat and need proper handling and encouragement to stick around instead of scattering.
Sometimes it’s challenging to establish a stable population of beneficials, and it can be expensive to buy multiple batches of bugs; but for a small area like a garden, this can be a feasible solution or at least give you an edge over the aphids. Of course, the most successful beneficial insects will be ones that are naturally occurring in your area.
Chemical Aphid Control
Chemical control is exactly what it sounds like. There are organically approved pesticides that are commonly used on certified organic farms. The most common is a chemical called pyrethrum, extracted from flowers in the chrysanthemum family. However, keep in mind that just because it’s extracted from flowers doesn’t mean it is non-toxic.
This is a potent pesticide and should be used judiciously and only applied using proper respiratory and skin protection. For a less effective but helpful and quick aphid spray, try this two-ingredient recipe, which I have found helpful in controlling, though not eradicating, infestations.
Quick And Easy Organic Aphid Spray
- 2 handfuls of tomato leaves
- 2 jalapenos
- 4 cups water
- Dice the jalapenos and crush the tomato leaves while boiling the water.
- Pour the boiling water over the greens and let sit overnight.
- In the morning, strain out the leaves and peppers, pour the mixture into a spray bottle, and go to town on your plants.
This spray is most effective in the very early stages of an aphid problem, not for dealing with an advanced infestation. In bad cases, manually scrape or remove leaves to reduce the aphid numbers before spraying.
Don’t rub your eyes while making this mixture!
Aphids are a fact of life on organic farms and homesteads, and not even the best management practices can prevent that. Often on crops like cabbage, the outer leaves with aphids can be pulled off and still leave plenty of edible or marketable vegetable. Washing vigorously with water will also take aphids off after the crop has been harvested.
Aphid Infestation Prevention And Management
It’s practically impossible to entirely prevent aphids in an organic manner. Reducing the pest “load,” or the relative amount of pests for the age of the crop and the size of the field is more important.
The very best way to manage aphids in the long term is intensive crop rotation, cover cropping, and fallowing. Luckily, aphids only prey on certain families of plants, and different varieties of aphid specialize in different plant families.
For example, cabbage aphids love cabbages, kale, cauliflower, broccoli, and will sometimes eat legumes with juicy leaves like peas. On the other hand, green peach aphids, which are actually an entirely separate genus, prey on solenaceas like tomatoes and peppers, and on cucurbits like cucumbers.
So, even though both groups of plants get aphids, they can be rotated effectively because they are different populations. Be sure to cover crop at least once every three growing seasons with a grain like rye or wheat that is not susceptible at all to aphids. If serious problems persist, extend the rotation and only grow one aphid-susceptible crop for every two to three years in other production or cover crop.
Aphids can also occur in orchards, where crop rotation is not possible. In this case, it is vital to catch an infestation early. Check your trees every one to two weeks and prune or thoroughly hose down affected areas.
Since aphids can be harbored in weeds, like mustard, or in crops like cabbage being grown near trees, be sure to keep an eye on your surroundings also. Beneficial insects can be very helpful in orchard cases. If problems persist, spray whatever pesticide seems appropriate, in moderation.
Like humans, plants become more susceptible to pest damage and growth reduction when they are stressed by multiple things at once. Be sure to water your plants regularly, especially on hot days, and fertilize if needed.
Check out our article on soil testing and how to test and amend your soil. If you need help or have questions, contact your local agricultural extension office. Healthier plants won’t be bothered by a few aphids, and you can rest well knowing that your cabbage is feeding aphids, who are feeding ladybugs, who bring good luck to children who find them in the garden. As always, with organic agriculture, the goal is not total control but a beneficial balance.