Aphids are problematic in any garden. When milkweed plants are involved though, aphids become a bigger concern as they threaten the garden ecosystem.
What strategy you use for getting rid of aphids depends on the reason you planted the milkweed plant. In a butterfly garden, there is a biological ecosystem to control to prevent attracting too many beneficial insects.
Ladybugs and lacewings can be terrific in any garden at controlling aphid populations. In a butterfly garden, they are not selective and will eat the eggs and larvae of the Monarch butterfly.
Herein lays the problem.
Milkweed is the only plant the Monarch will lay eggs in. The plant is toxic to a wide range of animals. Monarchs are resistant to it.
They need it because it builds their integrated defense system. Predators leave them alone because they recognize the threat the Monarch poses.
Most aphids recognize the toxicity of milkweed too. Except for the Oleander aphid. These have a tolerance to the toxins in milkweed sap.
Both insects are attracted to all plants in the Asclepiadaceae including the subtropical Hoya plant.
Keep reading to uncover an all-natural strategy to getting rid of the oleander aphid, save the milkweed, and (possibly) monarchs, too.
How to get rid of aphids on milkweed
Oleander aphids feed on the milky sap inside the leaves of milkweed plants. In a butterfly garden, natural control methods should be used to prevent disrupting the lifecycles of butterflies. When infestations are out of control, beneficial bugs can reduce aphid populations to manageable levels.
Identifying oleander aphids
Oleander aphids are slightly smaller than regular aphids that are prone to draining garden plants of their sap. Regular aphids are around 4 mm in size. Oleander aphids are under 3 mm.
Despite being smaller, they are easier to identify as these are yellow or orange.
Like every other aphid species, they are asexual so their numbers can quickly inflate.
When aphids are on milkweed plants, the leaves, stalk, and flower petals look like they have developed orange spots on the plant.
The orange speckles are the oleander aphids.
They feed on all plants in the Asclepias family. On oleander plants, the aphids cause oleander leaves to turn yellow. Milkweed plants are a little more tolerant. Yellowing leaves on milkweed is usually indicative of over-watering. And that is what attracts aphids in the first place.
Pick them off by hand
Given the toxic nature of milkweed plants, and the yuckiness of bug squashing, wear a pair of gloves and rub the leaves and stems to crush the bugs.
This is sufficient when the numbers are low. Take regular walks around your garden from early spring to catch these before they start reproducing.
As these are asexual, it only takes one aphid to search out a milkweed plant, pierce into it to start feeding, enjoy the taste and decide to nest.
One solitary aphid is all it takes to start a colony
They give birth to live nymphs that start feeding right away and they are pregnant at birth. Those new nymphs can start dropping offspring and eggs in the soil within a week.
Eggs can overwinter in the soil. When they do, winged aphids can reemerge the following spring.
The only surefire way to stop milkweed plants from being overrun with aphids is to catch the problem early and kill the bug and all of its offspring.
Turn gunner with your garden hose
Water cannons are used for crowd dispersal. An alternative tactic to hand-to-hand combat. In the garden, you can deploy the same tactic to disperse hundreds of aphids in a matter of seconds from milkweed plants.
The higher the water pressure, the surer you can be that they will be dislodged from the plant.
As the majority of oleander aphids are wingless, when they get knocked off the plant, they are too weak to climb and without wings, they cannot get back up from the soil.
On and in the soil, wingless aphids starve
For any of the adult ones that do have wings, the daily glove-wearing for aphid crushing can keep the numbers in check.
When spraying to knock aphids off the plant, aim under the leaves. That is where most will congregate.
All the leaves will need a good soaking to rid them of excrement.
Aphids excrete honeydew that becomes a feeding ground for ants. If ants arrive, they can become protective of the aphid colony, protecting them from nearby beneficial bugs that would have them for breakfast.
Honeydew on the leaves blocks sunlight and starves the plants of air, water, and nutrients. The result is stunted growth, less nectar, and before long, black sooty mold. Fungal infections will arrive.
Generally, as soon as aphids make a start feeding on milkweed plants, the plant goes downhill rapidly.
The only way to help it survive is to keep on top of knocking off aphids off or killing them on the plant by rubbing them between your thumb and forefinger.
Biological controls for aphids on milkweed plants
A healthy garden will have insects. The tricky part for the gardener is having enough of the good bugs to fend off the bad bugs.
The good guys to have around include hoverflies, lacewings, ladybugs, and the parasitic wasp.
Despite being considered as good garden pests, they are meat-eaters and do not care what they eat. In butterfly gardens, some of the eggs or caterpillars can become food for these bugs too. They are not fussy.
They are heavy feeders though so once your aphid population is down, they fly away to find a richer food habitat.
Use insecticidal soap to wash the leaves
Insecticidal soap is an organic method of getting rid of aphids without harming the plant. Other methods are neem oil and horticultural oil.
An insecticidal soap sprayed on the leaves is only for use as a contact insecticide. To make a DIY mix, use a tablespoon of liquid castile soap in a half-gallon of water and use a spray bottle to drench the plant.
Leave the soap on for up to 15-minutes then rinse it off thoroughly. Only do this when temperatures are cool to avoid leaf burn.
Frequently Asked Questions related to getting rid of aphids on milkweed
Does neem oil harm caterpillars?
All oils leave behind residues and will poison caterpillars too. Caterpillars are considered pests so, in a butterfly garden, a neem oil soil drench will kill butterfly eggs and larvae. If that is not a concern, then neem oil can be applied the same way an insecticidal soap is used.
Is rubbing alcohol safe to use on milkweed to kill aphids?
Rubbing alcohol (70% isopropyl) is a contact insecticide. It will kill oleander aphids. In gardens where the aim is to use milkweed plants to raise Monarch butterflies, dab the aphids with a Q-tip soaked in rubbing alcohol. Do not spray the alcohol as it will kill monarch eggs, too.
Marcel runs the place around here. He has a deep passion for houseplants & gardening and is constantly on the lookout for yet another special plant to add to his arsenal of houseplants, succulents & cacti.
Marcel is also the founder of Iseli International Commerce, a sole proprietorship company that publishes a variety of websites and online magazines.