How to Get Rid of Aphids Without Killing Beneficial Insects

The Short Answer

To get rid of aphids without killing beneficial insects, wash them off with a strong spray of water, prune out the few shoots where they are packed together, and use insecticidal soap or horticultural oil as a spot spray only if those two steps fall short. Avoid insecticides that leave a lasting residue. Before doing any of it, look for the predators that may already be at work, because a colony under attack often collapses within a week or two with no help from you.

The University of California’s integrated pest management program frames the starting point this way: low to moderate numbers of leaf-feeding aphids are not usually damaging in gardens or on trees. Control is for colonies that are large, growing or distorting new shoots.

Confirm It Is Aphids

Aphids have soft, pear-shaped bodies with long legs and antennae, and they may be green, yellow, brown, red or black depending on the species. The feature that separates them from other small insects is a pair of cornicles, which University of Wisconsin Extension describes as tailpipe-like structures projecting from the rear of the abdomen.

The second clue is honeydew, the sugary liquid aphids excrete. It makes leaves sticky, attracts ants, and supports a fungus called sooty mold that turns the residue black. Clusters of small insects on shoot tips or leaf undersides, sticky leaves below them and ants running up the stems together point to aphids. If you see holes or chewed edges instead, a different pest is responsible, such as the caterpillars covered in our tomato hornworm guide.

Speed is the reason to check often. UC IPM reports that aphids can develop from newborn nymph to reproducing adult in seven to eight days, and that each adult can produce up to 80 offspring in a matter of a week. It recommends checking plants at least twice a week while they are growing rapidly.

Look for Natural Enemies Before You Treat

Check the colony itself for evidence of natural enemies. UC IPM lists lady beetles, lacewings, syrphid fly larvae and the mummified skins of parasitized aphids. Colorado State University Extension calls aphids quite defenseless and singles out lady beetle larvae as particularly voracious predators. Those larvae look nothing like the adults, so learn them before you squash one by mistake.

Mummies are the most useful sign. When a parasitic wasp lays an egg inside an aphid, the aphid’s skin turns crusty and golden brown and stays stuck to the leaf. According to UC IPM, once mummies begin to appear, the aphid population is likely to be reduced substantially within a week or two. If the plant is not suffering, the best treatment at this stage is none.

The Least-Toxic Order of Attack

Each method below removes aphids, and each one further down the list is a little harder on the insects you want to keep. Start at the top.

1. Check plants at least twice a week and tolerate low numbers.
2. Look for lady beetles, lacewing and syrphid larvae, and mummies. If they are present, wait a week or two.
3. Knock the colony off with a strong spray of water.
4. Prune out curled leaves and infested shoot tips.
5. Spot spray insecticidal soap or horticultural oil on what remains.

Wash Them Off With Water

A hose is the first tool. UC IPM says most dislodged aphids will not be able to return to the plant, and the spray washes off honeydew as well. Colorado State adds that hosing may lethally injure aphids, and that very few of the survivors knocked to the ground find their way back onto the host plant.

Use a forceful jet and aim under the leaves and into the shoot tips, since that is where colonies sit. Water leaves nothing behind on the plant, so a lady beetle that lands an hour later finds a clean leaf and whatever aphids are left.

Prune Out the Worst Shoots

Aphids often concentrate on a handful of tips. Where a population is localized on a few curled leaves or new shoots, UC IPM suggests that the best control may be to prune those areas out. Check the cut pieces for lady beetle larvae and mummies before you bin them.

Use Soap or Oil as a Spot Spray

When water and pruning are not enough, insecticidal soap and horticultural oil are the next step. Our guides to reading an insecticidal soap label and to neem oil and horticultural oil explain what is in each product. They work by smothering, so thorough coverage of infested foliage is required. An aphid the spray does not touch is unharmed.

That same property is what protects beneficial insects. UC IPM explains that soaps and oils can kill some natural enemies that are on the plant and hit by the spray, but they leave no toxic residue, so they do not kill natural enemies that migrate in afterward. Colorado State describes insecticidal soaps as selective, with minimal hazard to beneficial insects. To keep that hazard small, spray only the infested parts of the plant, and move any lady beetle larvae you can see out of the way first.

Two limits apply. Soaps and oils kill only the aphids present on the day they are sprayed, so applications may need to be repeated. And UC IPM warns against using them on water-stressed plants or when the temperature exceeds 90 degrees F.

What to Avoid

Skip insecticides that persist on the leaf. UC IPM names malathion, permethrin and acephate as materials that kill the natural enemies providing long-term control, and says they are associated with bee kills. Colorado State makes the same point about persistent products in general: they may give better initial control of aphids, but they can have serious effects on aphid natural enemies. An aphid can go from newborn to reproducing in seven to eight days, so a garden stripped of predators gives the survivors a clear run.

Buying lady beetles is a gentler idea with a catch. UC IPM’s instructions are to keep them refrigerated until just before release and to let them go at dusk, because beetles released in broad daylight fly away immediately.

Keep Ants and Excess Nitrogen Out of the Picture

Ants collect honeydew, and in exchange they protect aphids from natural enemies. On trees and woody shrubs, UC IPM recommends a band of sticky material around the trunk to stop ants climbing. Ant stakes or enclosed baits on the ground are an alternative that controls ants without affecting aphids’ natural enemies.

Fertilizer matters as well. High levels of nitrogen fertilizer favor aphid reproduction, so UC IPM advises never using more nitrogen than necessary.

Plant Flowers That Feed the Predators

The adult stages of many aphid enemies eat nectar and pollen. University of Wisconsin Extension notes that many natural enemy adults, particularly tiny wasps and flies, visit flowering plants for both. Small, shallow flowers serve them best, because a tiny wasp gets lost in a big flower.

Wisconsin points to three plant families. The carrot family includes dill, fennel and cilantro. The aster family includes cosmos, coneflowers and coreopsis. The mustard family includes sweet alyssum. It also notes that yarrow is visited by many insects. Timing counts, since many natural enemies are active as adults for only short periods, and Wisconsin suggests sequential plantings of dill and cilantro so flowers are available all season. Our guide to companion herbs for pest control covers where to fit these plants among vegetables, and a pollinator garden that blooms from spring through fall keeps the same flowers coming for the whole season.