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Plant Answer Line Question

Keywords: Insecticidal soap, Citrus limon, Aphids

My Meyer lemon has aphids all over it and has lost its leaves! I just brought it inside for the winter. What can I do?


The aphids were more than likely already there, even if not enough for you to notice, and once inside the warm(er) house they multiplied. Aphids do love citrus plants. The leaves probably fell off due to the temperature change they experienced coming indoors.

The following information was found on p. 278 of the 2001 edition of the Sunset Western Garden Book:

Citrus in containers. Fertilize monthly from midwinter to mid-autumn with high-nitrogen liquid fertilizer, containing chelated zinc, iron, and manganese. Potted citrus ... in cold-winter regions: shelter plants in winter; a cool greenhouse is best, but a basement area or garage with good bright light is satisfactory.

Many of the common products sold in nurseries or garden centers contain the trace elements listed in the Sunset info above. Also, there are specific formulations for citrus available, also carried by many nurseries and garden centers.

...Sunset Western Garden Book continued...Citrus as houseplants. No guarantee of flowering or fruiting indoors, though plants are still appealing. 'Improved Meyer' and 'Ponderosa' lemons [other citrus names omitted] are most likely to produce good fruit. Locate no farther than 6 ft. from a sunny window, away from radiators or other heat sources. Ideal humidity level is 50 percent. Increase moisture by misting tree; also ring tree with pebble-filled trays of water. Water sparingly in winter...

I grow 2 Meyer lemons and find that they do best outside until the temperature goes down into the 20s. They are pretty hardy. The aphid problem is not a problem outside until spring. If you have a sun porch at your house, that might be a great place to put the lemon in winter.

As for the aphids, Colorado State University Extension provides information on insect control using insecticidal soap. You can purchase it or make your own: 1 teaspoon of soap (the mildest you can find) per quart of water, sprayed on both sides of the leaves and on growing surfaces.

Date 2019-09-19
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Plant Answer Line Question

Keywords: Insect pests--Control, Arctostaphylos, Aphids

My Arctostaphylos uva-ursi has suffered from galls caused by aphids. What approach would be best to combat the aphids and when is the best time in their life cycle to attack?


Kinnikinnick or Arctostaphylos uva-ursi sometimes suffers from galls caused by aphids, and is also susceptible to fungal diseases. If your plant has galls, you would see distorted, thickened, and often reddish leaves which almost don't seem leaf-like. The aphids may also secrete honeydew which can then turn blackish with mold.

Douglas Justice, University of British Columbia Botanical Garden Associate Director offers these comments on Arctostaphylos uva-ursi:

The Arctostaphylos uva-ursi cultivar 'Vancouver Jade' -- a UBC introduction and one of the most widely grown cultivars in temperate climates -- is adapted to wetter conditions than many other cultivars, as it was selected from the Pacific Northwest. Nevertheless, like all kinnikinnicks, it is not a plant for poorly drained, shaded or high traffic areas. And unfortunately, it appears to be rather more susceptible to manzanita pod gall aphid than other cultivars. Populations of that insect pest can build up during "warm winter" periods (such as we've been experiencing in Vancouver over the past several years) and disfigure plants significantly.
Source: UBC Botanical Garden Forums

Oregon State University has information about leaf gall on Arctostaphylos uva-ursi in their Plant Disease management handbook online.

The following, from Pacific Northwest Insect Management Handbook (WSU, OSU and U. of Idaho, 2005) provides more information about the aphids.

Kinnikinnick Arctostaphylos - Aphids

Manzanita leafgall aphid, Tamalia coweni:

Pest description and crop damage - Manzanita leafgall aphids are grayish or greenish in color and prefer new growth. They feed on the leaves of kinnikinnick and other manzanita species (Arctostaphylos spp.). Aphid feeding causes the leaves to thicken and form bright red galls. Older galls turn brown. Severe infestations may slow the growth of the plant.

Nongall-forming aphids also may be seen occasionally on kinnikinnick. They are greenish, soft-bodied insects that may feed on leaves or stems. Honeydew, a sweet, sticky material, may be associated with aphid feeding. It may attract ants or become covered with a growth of dark, sooty mold. Severe infestations may result in leaf and twig dieback.

Management-biological control: Syrphid fly larvae are important predators of leafgall aphids, and will feed on them inside the galls. Avoid use of broad-spectrum insecticides which kill these and other beneficial insects such as ladybird beetles and parasitic wasps.

Management-cultural control: Prune off and destroy galls where seen. Avoid frequent shearing and overfertilization, which encourages succulent new growth favored by aphids. Wash other aphid pests from plants with a strong stream of water or by hand-wiping. Avoid excessive watering, and use slow-release or organic sources of nitrogen. Control ants, which "farm" aphids and protect them from predators in order to harvest their honeydew.

Date 2019-08-14
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Plant Answer Line Question

Keywords: Plum, Aphids, Prunus

My prune tree has tons of aphids in the leaves (also a lot of ladybugs to eat them but I am not sure the ladybugs will win out). Do I need to try to rid the tree of the aphids? If so how?


The question of whether to control aphids in your prune tree really depends on how bad the infestation is and if the tree is otherwise healthy enough to outgrow them. Often infestations like aphids are a symptom of a larger problem. The tree may be stressed out by root competition from grass or too much or not enough water, too much or not enough nitrogen. A stressed out tree is attractive to aphids, who in turn attract lady bugs. My own mature prune tree gets covered in aphids every year. The leaves get distorted, and lady bugs come in droves. Some years I get a good harvest and some years I do not. I choose not to worry about it (I have other plants to fuss over). But if you feel the need to do something, see the HortSense website from Washington State University.

Date 2019-05-17
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Plant Answer Line Question

Keywords: Viburnum, Integrated pest management, Aphids

I have a small snowball bush that I planted three years ago. Each spring this plant is inundated with more and more ants and aphids. I try to garden organically and could use Safer Soap on it, but it is large and the leaves are all curled under and withering from the insects. Is there anything other than Safer Soap that I could use to help the plant, either systemic or otherwise?


Following are the best sources I have found about environmentally friendly control of aphids.

Aphids (order Homoptera)

Almost all plants have an aphid species that may occasionally feed on them. Many aphid species attack several plants rather than having only one host. Trees (esp. birch, beech, maple, apple, peach, apple, plum, cherry, spruce, dogwood, willow); annuals (esp. nasturtium, snapdragon); perennials (esp. lupine, roses, lilies, begonias, columbine); vegetables (esp. peas, beans, brassicas, lettuce, spinach); fruit (esp. apple, peach, cherry).

Small (2 mm long), pear-shaped, softbodied insects in a range of colors (green, brown, red, yellow, black). Most are wingless, but winged aphids appear at certain times, especially when populations are high or during spring or fall. A few species appear waxy or woolly. A magnifying glass will reveal the long, slender mouth parts used to suck plant fluids. Aphids are usually found in clusters, especially on new growth. Signs of aphid infestations include sticky honeydew on leaves or under plants, distortion of leaves, stunting of shoots, or large numbers of ants on the plant.

Life Cycle:
Overwintered eggs of some common garden species hatch in spring. These wingless females reproduce asexually, bearing live young (up to 80 per week) that already have the next generation developing inside. Young aphids, called nymphs, molt four times before becoming adults. There is no pupal stage. This simple, rapid reproduction allows for very large population increases in a short time. Late in fall, males and females are produced, mate, and the females subsequently lay eggs. Winged aphids may appear at certain times, allowing the colony to move to other locations. Not all aphid types have this reproductive pattern, but many do.

Natural Enemies:
Aphids have many natural enemies, including birds, spiders, ladybird beetles, lacewings, syrphid fly larvae, and braconid wasps. A naturally occurring fungal disease can also kill aphids when conditions are right. Ants have a symbiotic relationship with aphids: ants milk the aphids for honeydew while protecting the aphids from natural enemies.

Check plants often, since aphid populations can rise rapidly. Inspect growing tips and undersides of leaves. On trees, clip off leaves from several parts of the tree to look for aphids. If you see large numbers of ants on tree trunks, check for aphids on limbs and leaves. Look also for associated signs, such as yellowed leaves, stunted or distorted growth, or dripping honeydew. Sticky traps can be used to monitor for winged aphids. Check for signs of predators (named under Natural Enemies above), aphids that have been parasitized (look for a small exit hole on a dead, brown aphid body), or that have been killed by disease. Substantial numbers of any of these natural control factors can mean that population numbers will fall rapidly without the need for treatment. Because of the rapid changes that can occur in aphid populations, it is important to record monitoring data to detect changes due to predators or treatments.

Action Threshold:
Due to the incredibly high numbers that may be present, counting individual aphids is usually not practical. Action thresholds can be based on general descriptions of aphid density, plant damage such as stunted or distorted growth, or unacceptable amounts of honeydew beneath trees. Treatment should be triggered by rapidly rising numbers, unacceptable plant damage, or by honeydew falling on structures and people. Aphids seldom kill a plant, but they can cause defoliation. They also carry diseases from one plant to another. It is usually not necessary or even desirable to treat at the first sign of aphids, since low populations are needed to sustain predators.

Cultural/Physical Controls:
Plant selection: If possible, avoid or consider replacing varieties such as birch that have ongoing, serious aphid problems. Check transplants for aphids and remove them before planting.

Water spray: A strong blast of water knocks aphids from the plant, and most will not return. Water also helps rinse off the honeydew. Do this early in the day to allow leaves to dry and minimize fungal diseases.

Pruning: Where high aphid populations are localized on a few curled leaves or new shoots, prune these areas out and drop in soapy water to kill the aphids.

Fertilization control: High nitrogen levels favor aphid reproduction. Avoid over-fertilization and use slow-release rather than highly soluble fertilizers.

Sticky or teflon barriers: If you see ants crawling up the trunk of trees or other woody plants, place a band of sticky material (such as Tanglefoot or Stik-Em) around the trunk. Place a protective band of fabric tree wrap or duct tape underneath the barrier first. Teflon tape barriers may also be effective. Prune out branches touching the ground, buildings, or other plants.

Biological Controls:
Since aphids have many natural enemies, biological control usually means protecting these enemies from ants and avoiding broadspectrum pesticides that kill beneficial insects. Recognize that predator populations usually lag behind aphid populations in time. A number of aphid enemies can be purchased for introduction into landscapes. Ladybird beetles, lacewings, and parasitic wasps and flies are all available. Although such introduced predators may not remain where released, some benefit is likely, especially if releases are staggered in time. Many of the natural predators of the aphid are especially attracted to a garden with plants in the Umbelliferae family, such as angelica, sweet cicely, dill, and Queen Anne's lace. The flowers of these plants provide a good food source for insects, especially parasitic wasps, who may stay to prey on some aphids as well.

Chemical Controls:
Insecticidal soap is widely recognized as the least-toxic chemical aphid control. Although its effect is temporary, it can help to bring aphid numbers down so that natural enemies can take care of them. Repeat applications within a few days may be necessary. Soap works only by direct contact with the insects. Be sure to cover both sides of the leaves. Although readily biodegradable, soaps are highly toxic to fish, so avoid runoff or direct application to water. Avoid using when temperature exceeds 90 degrees F.

Oil sprays:
Supreme or superior-type oils will help to kill overwintering aphid eggs on fruit trees if applied as a delayed dormant application in early spring. Although perhaps not justified for aphid control alone, oils can also control other overwintering fruit pests. Oils may, however, kill some beneficial species. Summer weight oils are also available, but they can burn tender leaves when applied in hot sun.

Conventional chemical control:
Foliar applied insecticides (malathion, diazinon, carbaryl, pyrethrin) are broad spectrum and will kill beneficial insects. They should be avoided, especially in home gardens and landscapes. Remember that allowing some aphid population in the garden helps to keep predators available.

ProIPM Integrated Pest Management Solutions for the Landscaping Professional
The Green Gardening Program is a collaborative effort of Seattle Tilth, Washington Toxics Coalition, and WSU Cooperative Extension, King County.
Sponsored by the Seattle Public Utilities in an effort to promote alternatives to lawn and garden chemicals.
Funded by the Local Hazardous Waste Management Program in King County.
Written by Philip Dickey, Graphic Design by Cath Carine, CC Design

Pest description and crop damage:
Aphids are soft-bodied insects that typically feed on leaves and succulent stems. They may vary in color from pale green or reddish to dark or black. Aphids are usually less than 1/8 inch in length.

Feeding damage to the plant is usually minor, although some leaf and shoot distortion can occur if populations are high. Aphids also produce honeydew, a sweet, sticky secretion that collects on plant tissues and encourages growth of a black sooty mold. This can interfere with photosynthesis of the plant. Honeydew is also a nuisance when it falls on decks, cars, or other landscape surfaces. They are a problem in early summer.

Biology and life history:
Most species of aphids have similar life cycles. Aphid females give birth to live offspring all year without mating. When other hosts are not available, aphids live on a wide variety of weeds. Aphids usually are found in colonies on new growth, the underside of leaves, and near flower and fruit clusters. In summer and fall, aphids may produce winged females and, later, winged males. They mate and produce eggs for overwintering, especially in colder climates. Otherwise, adult aphids overwinter on crops, weeds, or trees. There may be as few as 2 or as many as 16 generations each year, depending on the species and climate.

Management & biological control:
Aphids have many natural enemies, including lady beetles, syrphid fly larvae, and green lacewings. Avoid broad-spectrum insecticide applications that would disrupt these controls.

Management & cultural control:
Wash aphids from plants with a strong stream of water or by hand-wiping. Aphid populations tend to be higher in plants that are fertilized liberally with nitrogen and heavily watered, as this produces flushes of succulent growth. Avoid excessive watering, and use slow-release or organic sources of nitrogen. Control ants, which farm aphids and protect them from predators in order to harvest their honeydew.

Management & chemical control (home):
It is important to cover foliage thoroughly, including lower leaf surfaces.
1. Beauveria bassiana
2. horticultural oil
3. insecticidal soap


Date 2019-12-07
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Plant Answer Line Question

Keywords: Aphids, Betula, Trees--Diseases and pests

I have just taken over management of the small landscaped yard for my condominium and we have two trees (weeping birches I've been told) in the front that appear to have been infested with aphids. The trees are about 15 feet tall and are located between the building and the sidewalk to the entrance. They have southern exposure. There's a few evergreen bushes around the trees, no grass.

I am not familiar with aphid controls, so have done some internet research, including your very useful site. We want to avoid using pesticides, so from what I've read, the best control is insecticidal soap. Before I try to spray this on the trees I have a few questions I was hoping you could answer. 1. Can you verify that this is aphid damage? 2. It seems to me that the amount of white material on the undersides of the leaves has decreased in the last month. Given that it is getting late in the growing season, is it still worth treating the trees? 3. Does insecticidal soap seem like a good treatment in this situation, and if so do you have any application tips to make sure the undersides of the leaves are treated? 4. Do you have any recommendations for preventative actions to decrease the impact of aphids on these trees in the future?


Birches are commonly afflicted with aphids, and the aphids suck sap and secrete honeydew, which can be a nuisance, and is usually why homeowners contact us. Unfortunately, if your birches are overhanging a sidewalk, it is probably getting sticky from the honeydew. Otherwise, you could probably ignore the problem (except in the most severe infestations).

You can try spraying the aphids off the leaves with a strong jet of water. You can also encourage natural predators. Avoid over-fertilizing, or exposing the trees to lawn fertilizer, for example, as this will lead to succulent new growth which attracts aphids. Make sure the trees are not under any stress, as aphids are more likely to feed on a weakened tree. You may be able to avoid using the insecticidal soap as a control. If you do use it, you are correct that you need to reach all leaf surfaces, which is labor-intensive. Some of these soaps can cause damage, so it is always a good idea to test any such spray on a small area before coating the whole plant. An article by Colorado State University Extension provides information on insecticidal soaps. Aphids go through many generations in a year, and their eggs can overwinter.

Toxic-Free Future (formerly known as Washington Toxics Coalition) has created a document on managing aphids in the landscape.

Here are additional links on aphid control:
Aphids from University of California at Davis
Managing Aphid Problems without Pesticides from the Northwest Coalition for Alternatives to Pesticides

Date 2019-10-10
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Plant Answer Line Question

Keywords: Alyssum, Aphids, Apples--Diseases and pests, Beneficial insects

Is there something I can do to prevent my apple trees from getting woolly aphids? I'd rather not have to spray anything.


Encouraging beneficial insects is one step you can take. A 2013 study at Washington State University found that planting Alyssum flowers attracted syrphids which did a good job of reducing woolly aphid populations. Here are highlights of the paper that was published based on the study's findings:

  • Sweet alyssum flowers had the highest attractiveness to syrphids.
  • Faster suppression of woolly apple aphid occurred on trees closer to alyssum flowers.
  • Higher densities of natural enemies were observed near sweet alyssum plantings.
  • Natural enemies were found to move between sweet alyssum and adjacent apple trees.

As Washington State University's HortSense website (search under "tree fruit," "apple," then "aphids") indicates, encouraging beneficial insects is a good practice for the control of all 3 main types of aphids affecting apples, be they woolly, rosy, or green:

  • Control honeydew-feeding ants, which may protect aphid colonies from predators.
  • Encourage natural predators including ladybird beetles, lacewings, syrphid (hover) fly larvae, and parasitic wasps. Avoid use of broad-spectrum insecticides which kill these beneficial insects.
  • Hand-wipe or prune to control small, localized infestations (when practical).
  • Provide proper nutrition. High levels of nitrogen encourage aphid reproduction. Switch to a slow-release or low-nitrogen fertilizer.
  • Wash aphids from tree with a strong stream of water before leaves curl.

Date 2019-06-13
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Garden Tip

Keywords: Aphids, Organic gardening

Many plants outgrow aphid infestations with no harm done. But sometimes aphids do cause permanent damage to tender shoot of young plants. If action must be taken, soft-bodied aphids can be killed by common non-toxic ingredients found at home. Here is a recipe for a spray from The Frugal Gardener by Catriona Erler (Rodale, $27.95):

  • 1 garlic bulb
  • 1 small onion
  • 1 teaspoon cayenne pepper powder
  • 1 quart water
  • 1 tablespoon liquid dish soap
liquefy garlic and onion in a blender, then add cayenne and water. Steep for an hour. Strain the liquid through cheesecloth, then add soap. Spray directly on aphids, or on plants vulnerable to aphids, like roses. Keep away from eyes and skin. This spray may be kept refrigerated for one week.

Date: 2007-02-26
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Garden Tip

Keywords: Aphids

As plants surge with new growth, the pesky aphid experiences a population explosion. Many plants will simply outgrow the aphid attack with nothing more than a rinse of water. But in other instances aphids can cause distorted growth, spread viruses, and generally weaken the host plant. UC Davis publishes an excellent guide to managing aphids in the garden using Integrated Pest Management, the practice of matching the appropriate, least toxic solution for garden pests: www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7404.html

Date: 2006-02-28
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