Aphids on Milkweed – what to do

One of the truths when growing milkweed is that you not only get milkweed, but you also get other bugs which love milkweed – besides monarch butterflies.

Aphids are the main pest, but also you may get quite a few of the milkweed bugs.

Here are some possible solutions:

  • Do nothing – aphid populations will rise and fall. In nature this is just part of the natural process of life. They will eventually draw predators to their location.
  • I have found that most aphid populations die off around July 4th in St. Louis. One theory is that the aphids get infected with a disease that kills them off. The aphids are all clones, so if one is infected, the others will should get the same infection. The other theory is that the predator population has built up by this time and controls the population.
  • I have taken to spraying the milkweed with water when I have aphids. My theory is that it might encourage viruses and disease which might kill off the aphids.
  • Inter-planting with cover crops is another solution I have found which worked well. The aphids have a harder time finding the milkweed when it is surrounded by other plants.
  • Flaming the plant bed is another solution I have heard of. You obviously do this before you plant. It should kill any eggs which may have over-wintered.
  • Before you do anything else check for monarch eggs and larva. You don’t want to injure them.
  • If everything is clear, you can try a simple blast with a garden hose. They will cling on, but with persistence you can get some of them off your plants. Unfortunately, they seem to find their way back.
  • You can then try a soap and water spray – I’ve tried it and it works. I’m using about 1T dish soap in one quart of water. Most sites say not to do this in hot weather as it hurt the plant. All of the black spots are dead aphids. I have noticed that while the leaves don’t seem to be affected, the blooms whither away with this soap spray, so soap is not quite innocuous as I’d like.
    I won’t do this again.
  • If infestations are terrible, you can simply clip off the infested area and dispose of them.
  • My final solution is to use an oil spray made for plants. Again check for monarch eggs and larvae. This will definitely kill the aphids, but will also kill other insects. Having an oil spray on the leaves and flowers where monarchs will lay their eggs is questionable, so I avoid doing this.
  • I generally don’t worry about milkweed bugs unless I get a lot. You then just use a soapy water solution in a container and knock the beetles into the container.
  • It’s interesting to me the many bugs you will find on milkweed. (click here)

Note – as I was writing this I noticed one Monarch egg and one lady bug which just goes to show that you have to be careful when working with pests.

If you want to learn more about aphid reproduction, watch David Attenborough’s Natural Curiosities – Season 2 #1 – Virgin Birth. It’s available on Netflix.


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Filed under Milkweed, Pests

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