When aphids suck the life from your milkweed, here's how to safely get rid of them

The dreaded oleander aphids have arrived here and are trying to wreak havoc in my gardens. At a friend’s house today, I noticed that all of her milkweed is infested beyond hope….Are there any new ideas on how to deal with them? Thanks. –Jan LeVesque, Minneapolis

Jan LeVesque is not alone in her exasperation at the hands–rather, mouth parts–of plant sucking aphids.  Anyone who raises milkweed in an effort to attract Monarchs is familiar with the soft-bodied, squishy orange insects that seemingly take over anything in the Asclepias family.

Oleander aphids on Tropical milkweed
If you raise milkweed and Monarchs, you’re well acquainted with oleander aphids. Here they are on Tropical milkweed. Note the sticky, slick looking substance on the leaves. That’s honeydew. Photo by Monika Maeckle
Jan, like many before and after her, posted the above query on the Monarch Watch DPLEX list, an old school listserv that goes to hundreds of citizen and professional scientists and butterfly fans who follow the Monarch migration. And as usual, the community had plenty of ideas.
But before we explore how to kill them, let’s take a look at the interesting life cycle of these ubiquitous, annoying insects, known as oleander aphids, milkweed aphids, or by their Latin name, Aphis nerii.
First off, they are parthenogenic, which means they clone themselves and don’t require  mates to reproduce. In addition, the clones they produce are always female.  Yes, that’s right–all girls. “No boys allowed.”
apids
All female aphid colonies undermine our milkweeds. Photo via University of Florida
According to the University of Florida’s Department of Entomology and Nematology “Featured Creatures” website, “The adult aphids are all female and males do not occur in the wild.”  Instead, the aphid moms deposit their all-female nymph broods on the stalks of our milkweed plants.  That generation morphs four more times until they grow up to become aphid moms who repeat the process.
Even more interesting, under normal conditions, adult female aphids do not sport wings, but get this: if conditions are crowded, or the plant is old and unappetizing (which happens as the summer progresses in our part of the world), the girls grow wings so they can fly away to greener pastures–or in this case, fresher milkweed. Aphids live 25 days and produce about 80 nymphs each.
This brilliantly efficient method of reproduction, says Featured Creatures, is one of the reasons “large colonies of oleander aphids…build quickly on infested plants.”

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Small populations of aphids are pretty harmless to the plants, but when you get a large colony, the milkweed suffers. The aphids insert their piercing mouthparts into the milkweed, literally sucking the life out of it as they enjoy the sweet liquid that courses through the plant. The high concentration of sugar in that liquid means the aphids have to eat a lot of it to get the protein they need.
That results in a profuse amount of excrement, called honeydew. It is prolific and forms a thin, sticky layer on the leaves of your milkweed, choking the absorption of essential nutrients.  It can also cause sooty mold, an ugly dark fungi that can cover your milkweed.

We have a fair amount of milkweed near the house and it’s been aphid free so far – except for one incarnata shoot on which a 3 inch long colony had formed with probably more than 500 aphids of all sizes. Not having mixed up any fancy aphid remedy and not having insecticidal soap, I looked under the sink for the handy spray bottle of 409. It wasn’t there – so, I grabbed the Windex instead. Last evening a quick inspection showed that all the aphids were blackened and dead. I checked again this morning and spotted one aphid. The plant seems unaffected by the treatment.  –-Dr. Chip Taylor, Founder of Monarch Watch

Once you have well-established infestation of aphids, the plant just goes downhill. The aphids themselves are also highly appetizing to Ladybugs, wasps and syrphid flies–all insects that eat aphids and Monarch or Queen eggs with equal abandon.
When I get a serious aphid infestation, I typically use a high pressure spray of water to blow the bugs off the plant. That simultaneously washes the honeydew off the milkweed, which will deter the arrival of ants and also clean the leaves so they can absorb sun, air, water and nutrients to fuel their growth.
My other method is to simply squish the aphids between my thumb and fingers and wipe them off the plant. Your thumb and fingers will turn bright gold, but will wash off.

Oleander aphids
A Ladybug’s favorite treat: aphids. Photo by Monika Maeckle
Some gardeners like to use alcohol or other additives with the water spray, but I prefer to keep that stuff off my plants.
As Dr. Karen Oberhauser of the University of Minnesota and founder of the Monarch Larvae Monitoring Project wrote to the DPLEX list in July of 2015, “Detergent treatments will kill any live insects on aphid-infested plants, including Monarch eggs, Monarch larvae, and aphid predators like syrphid fly larvae, ladybug larvae, and lacewing larvae.”
Alas, even Dr. Oberhauser, who has decades of experience with aphids, admits “There is really no good way to kill aphids without killing everything else, except by trying to lower the population by carefully killing them by hand.”

If Monarch cats are not present, I spray with insecticidal soap and then rinse later with water hose. If that is ineffective, I move up to Neem oil and rinse it off also later. One and/or the other are very effective…. It is easy to go from 1 to 1,000s of aphids in a very short period of time.
— David Laderoute, Coordinator,  Missourians for Monarchs

Another option is biological control. Lady beetles or Ladybugs feed primarily on aphids. Somehow they seem to magically find their way to our milkweed gardens to feast on the yellow critters. Ladybugs can be purchased in bags at some garden centers and released to do their jobs.  But remember–they also eat butterfly eggs.
Hover flies and wasps also eat aphids. Wasps have a bizarre practice of laying their eggs on the aphids, then eating them from the inside out, leaving a brown shelled carcass in their wake. We often find these hollow corpses on our milkweed plants.

Boo-hoo! Dead Monarch caterpillars fall victim to pesticide laced milkweed
Pesticides will kill aphids, but they often remain in the plant for months and will also kill Monarch caterpillars. Photo by Sharon Sander
One good thing about aphids: if you see them on a plant in a nursery, you know the milkweed is clean, and has NOT been sprayed with systemic pesticides. We all want perfect looking plants, but the occasional aphid is a good sign that your plants are pure. See this post for more on that topic.
Need more ideas for getting rid of aphids?  Check out this useful post from The Monarch Butterfly Garden.  If you have new tips not covered here, please leave a comment below.  Good luck!
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24 Responses

  1. Joe Barbosa
    | Reply

    I’m new at raising Monarchs. One of the first articles re raising Monarchs mentioned NEEM OIL to get rid of aphids. I used on my milkweed plants. NEEM made the leaves looked great. It also killed aphids and 14 caterpillars.
    Eventually found two outstanding sources to mentor with: Tony Gomez at monarchbutterflygarden.net and Monika Mackle at texasbutterfly ranch.com.

  2. Rita
    | Reply

    I have tried EVERYTHING on our tropical milkweeds to control oleander aphids. Most of the plants have been destroyed. After spending hours of squishing and rinsing with water, they come back with a vengence OVERNIGHT!! Taken advise from local nurseries. One even suggested to leave the aphids alone….really? We do see beneficial insects, but not enough to keep these little vampires in check. Happy to offer monarchs nectar plants, but done with milkweed for now!!!

  3. Norma Sheridan
    | Reply

    I have tiny pale green bugs that look like eggs but when you touch them they crawl away can you tell me what they are I am very. new at this and thought at first they were monarch eggs

  4. Leslie Williams
    | Reply

    One of my milkweed plants looks all but dead!! It has 1 caterpullar on it and LOTS OF THE YELLOW APHIDS AND MILKWEED BUGS. Loiks like the aphids wete crawling all over my caterpillar!! Will this kill the cat? I will be picking them off with tape as suggested!!

  5. David Perkins
    | Reply

    Spray a weak solution of lemon detergent and water directly on the little buggers. The acid in the lemon dries them up quickly. Use it sparingly so whatever eggs and cats might be around don’t get hit by it. I’ve not found any dead caterpillars since I started using this mixture.

  6. eileenpfeffer-robertson
    | Reply

    I have sent questions from my i- phone to you on your website and cant find any response! i have subscribed from my i-phone and my lap top! Help!!

  7. mark42mc
    | Reply

    I have a somewhat remedy I have for you all. I grow milkweed to raise monarch butterflies and I have been getting a lot of spider mites lately. So I was talking to a rose keeper and they use small shop vacs with a small amount of water and soap in the bottom of the container they suck them off when they hit inside of the container of the Shop-Vac they died because of the soap water. give it a try maybe between that and other things from above you might solve the issue I hope this works for you all take care. Thank you all for your help doing your part for the monarchs….🐛🐛🐛

  8. Estelle lowe
    | Reply

    Won’t the windex hurt the eggs and the catapillers

  9. Betty
    | Reply

    Great article except that there are insecticides that do not harm aphids and will harm monarch caterpillars . So seeing aphids on a milkweed plant does not mean the plant is safe for monarch caterpillars to eat .

    • Rob Wood
      | Reply

      Can you list some common garden insecticides that kill Monarch butterflies, but not aphids? That would be very helpful. Thanks!

  10. Lu Irkhart
    | Reply

    Hello, I just found this article. I was not actively growing milkweed, however I now have two good sections of plants. I have never noticed the bright orange aphids till this year. The black blight is in a patch on the ground and then I noticed the aphids. So I didn’t have them when they were blooming but now in the fall they are spreading very fast, in very large numbers. I’m in Southern Ontario and we had a very long wet summer with a short heat wave this past week. The pods are being sucked dry. I hand squished and drowned some of them and I guess will continue with water and squishing. Thanks for the information, I have to go through the rest of the website. Regards.

    • Val
      | Reply

      You are VERY lucky the little orange devils just showed up! they are a southern species that do not overwinter in northern areas. They blow up on the wind in the summer and always reach my location in Missouri by the summertime! Soap and water, water spray or squishing are the organic way to go, but there are many non-organic ways if monarchs are not present…if you are so inclined. Just because you have them now does not mean they will return without the right combination of weather conditions. According to one researcher, the Aphis nerii, Oleander aphids, change the chemistry of the plant in a way favorable to monarch caterpillars, so no worry there. If you are collecting seeds, I think the various seed bugs are more harmful than the aphids…but not sure. I consider you lucky as I know I will have these orange devils next year…without a doubt!

  11. Rob Wood
    | Reply

    I’ve had success with the squashing by hand method. I started doing this several weeks ago, and not only are aphids now rare on my milkweed, the plants themselves have recovered, and have become lush and full. The trick is that you have to do this a couple of times a day, whenever you see a cluster (or even one aphid). Eventually, there will be fewer and fewer aphids. I really have to hunt for them now.

  12. Val
    | Reply

    Has anyone tried diatomaceous earth? Wet or dry method. My theory is it should work…but think I need to add a wetting agent/dish soap. Does not seem to be working fast enough for me.

  13. Joyce Bennett
    | Reply

    I tried hydrogen peroxide because I had a small spray bottle at hand. It killed them but I don’t know about the lasting effect.

  14. Teresa Khouw
    | Reply

    Hello, I have found an extremely large cocoon attached to the outside brick of my house. It’s high up above rose bushes. Any idea what it may be? I’d like to try and include a photo. Description: soft, threadlike fibers, approx. 3″x4″, square, off white. I live in Dallas, Texas.

    • Monika Maeckle
      | Reply

      Impossible to guess without a photo.

      • Teresa Khouw
        | Reply

        I do not know how to attach a photo here. If you will please contact me thru my email, I will gladly include a photo in response to you.
        tkhouw@tx.rr.com

  15. Laura Segala
    | Reply

    I use scotch tape or masking tape to remove aphids from my milkweed plants. The aphids easily stick to the tape, which does not hurt the plants. Then I fold the tape over and throw it away. If you do this every few days in your garden, you won’t have that many aphids overall.

    • Monika Maeckle
      | Reply

      Great idea! Hadn’t heard that one. Thanks for sharing. –MM

    • Barbara
      | Reply

      Fantastic idea. Just cleared out the whole bunch in only a few minutes. Thanks!

  16. DORLIS GROTE
    | Reply

    why can I not pin these articles on pinterest to save them?????????? FRUSTRATING!

  17. DORLIS GROTE
    | Reply

    I like the smash and scrap away method. That way I control what I am killing. This year in north eastern Missouri has been a weird weather year and either it was too wet or too hot and the milkweeds did not do well. Also, we have not had many mosquitos or aphids or milkweed bugs.

  18. mary lenahan
    | Reply

    Hi,
    Thanks for the post! I’ve followed your blog for quite some time and always enjoy reading your articles.
    One bit of caution on buying ladybugs-the ladybugs that are sold in garden centers are Asian ladybugs. These become invasive and take the place of the native ladybird beetles.
    Check out this great site that I’ve used in my classes in the past.
    http://www.lostladybug.org/
    Thanks again for your informative blog!

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