July 1, 2020

Milkweed and the yellow aphids?

Milkweed and the yellow aphids- Bob Sussman

A couple of years ago a mom came to the nursery to buy some milkweed plants for her daughter’s school classroom. I walked her to the milkweed department. She quickly saw the yellow aphids…”what’s this?” Why those are yellow aphids….she turned around, hair on fire, as she quickly walked out of the nursery….I thought to myself something like “must be city folk.”

If you see yellow aphids on milkweed plants at the nursery it good news and bad news. The good news is they nursery hasn’t been using pesticides which would also kill your caterpillars. The bad news is you really do have to get rid of them.

Yellow aphids or Aphis nerii are a pest, not native nor are they a danger to monarch (or queen ) butterfly caterpillars but they are a danger to your milkweed plants as they feed on the milkweed and suck on the sap from the stems. This results in smaller and less vigorous milkweed plants and smaller less vigorous plants will feed fewer caterpillars.

The yellow ahpids form and reproduce along the stems and the underside of the leaves.

Now, how do you get rid of them? First don’t spray them with any sort of pesticide that will kill the aphids because it will also pretty much poison the plant and therefore poison/kill your caterpillars. …..What to do????

You want to kill the aphids and not poison the plant. Do this, spray your milkweed with dish soap at a rate of 1-1/2 oz to 2 oz/ gallon of water. This will work and it’s cheap. You want to use this low concentration or you’ll also burn the leaves. Not making this up…

Any dish soap will work just fine. After you spray you milkweed yellow aphids, take a look the next day and  you’ll see many have dropped off your plant and/or turned black. By the second day they should have all dropped off your milkweed plants and they are good to go.

The dish soap will be good for a while but they’ll be back and in a few weeks you’ll have to give them another dish washing treatment.  You can do this all summer until fall.  Fall is another monarch mating season. So in fall when you see caterpillars hold off on the dish washing soap spray the caterpillars don’t like it.

Some people try neem oil but the oil/water mixture separates quickly. You can also try ladybugs but these tend to fly away. Sometimes the ladybugs will find your aphids on their own. If you see a ladybug on your plants they’ll do the job too and will fly away when the job is done.

It’s always a balance to get the biggest milkweed plants with no…no… pesticides.


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Featured Plant



Botanical Name

Symphoricarpos mollis

Common Name



Flower Color


Mature Size

1-1/2 tall × 1-1/2 wide

Climactic Requirements


Full Sun / Filtered Sun / Part Shade


Occasional / Moderate
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