Friday, June 12, 2009

Goldenrod aphids


I was so excited to find aphids on some of my goldenrod (Solidago missouriensis)- my garden is all coming together.


Every gardener knows a thing or two about aphids. They are usually green or dark-colored and are one of the most common garden pests. They have sucking mouth parts, and their mortal enemy is the ladybird beetle (Coccinella spp.), aka ladybug.


Less known is that most native aphids are host-specific, that is, they only feed on one or a group of closely related plant species. The neat thing about the aphids in my photos, Uroleucon nigrotuberculatum, is that they are red (so they are easy to spot on a goldenrod stem). This is a relatively rare aphid that feeds on tall goldenrod species.


In the literature, this species is well studied because it demonstrates some important theories of predator-prey relationships. As the patch size of the host plant gets bigger, the rate of predation on the aphids goes up. I guess in our yard now we have patchy goldenrod, and thus a great home for these aphids and the native ladybird beetles they attract.



On garden plants the wingless females are the first ones that are visible, but as their population grows or as pressure from predators increases, individuals are induced to produce wings and fly off to colonize new areas.


Delighted with these aphids appearing on a few goldenrod stems, I looked them up on the Internet to find other gardeners which which to share my delight. There must be many already delighted gardeners out there, I thought, with the proliferation of wildlife gardening, pollinator gardens, green gardening, and so on. However... I was socked at what I found. Cue the scary movie music and read on.

There were, indeed, a bunch of websites with information about goldenrod aphids.... (wait for it)... and how to kill them! Even the gentle methods destroying them and their kin with earth-friendly (not aphid-friendly) biodegradable, free range, organic, etc... insecticidal soaps.

Here is a typical thread:
Question- What are these ugly red bugs?

Answer- Aphids. You had better kill them before they kill you and your family

Question- I knew it, they looked gross. I will kill them, but how? How can I kill them without using chemicals? I am a green, earth-friendly, holistic gardener.

Answer: Use a hose and spray them off

Question: Will that kill them? I don’t want them out there, doing damage to other plants, I want them dead, after all I care about the environment and all the creatures in my garden.

Answer: Use organic soaps, rub the soap into their soft bodies, and even squish them with your hands. Don’t let any get out of your sight, they can clone themselves and they may have already laid eggs, so plan of several treatments.

Great.

You should not just go around killing things. Try to understand the biology and ecology of animals and pests, first. These aphids, like many other aphids on plants in your yard, will not affect any other plants other than the ones they are feeding on, in this case goldenrods, and their effect on goldenrod is negligible. Furthermore, since they attract ladybird beetles and their larvae, the aphids are probably a very beneficial pest in your garden.

Speaking of ladybird beetles, commercial ladybird beetles sold as bio-controls for aphids is a booming business. Using for aphids and other pests is often thought of as a better, safer alternative to other control methods. However, as a result of their popularity, several of the common ladybird beetle species in North America are actually invasive species from Europe or Asia. These were introduced to this country as bio-controls, by well- intentioned gardeners. Some species of non native ladybird beetles are now the most common ones in the mid-west and elsewhere in the US.

Let me close by saying that I do squish aphids on my vegetable plants, but not because I'm afraid of them going to my goldenrods.

12 comments:

  1. So funny. "You should not just go around killing things." I'll keep that in mind. It was great to meet the aphids in person today.

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  2. Hi Kim,
    I guess that advice transcends gardening - you could apply it to your everyday life.
    Great seeing you today, I look forward to your next book.
    David

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  3. Another great article. You can kinda blame rose-cultivators for demonizing aphids. Just Google rose and aphid and you'll see what I mean.

    Frankly, because the aphids attack in early spring when roses are not blooming, I don't see what the big deal is. They make great prey animals and attract cool stuff.

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  4. I just try to ignore the aphids on my roses. After a while they're gone.

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  5. Great post! Now I'm starting to wonder what those aphid-like things are that I have on my Lonicera hispedula. I do believe it's nothing nice, have only seen them in the garden, but maybe I should do a bit more research.

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  6. Thank you ! I was a bit startled to see my goldenrod covered with these aphids when I got home from a trip. They appeared to be "infested". Now that I know that they attract ladybird beetles and are harmless they will stay where they are--I'm fascinated that they are species specific ! I am in Wisconsin.

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  7. I'm always impressed at how the yellow aphids find any asclepias I plant. Personally, I find the asclepias aphids ornamental until the population gets too big, then I give them the hose treatment. They did spread to the vegi garden one time when I let the population get too big and happy.

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  8. Hi, I noticed that my goldenrod bush is absolutely full of dark brown aphids. They've moved onto my liatris (right next to it). Should I be worried? I have the bright red aphids on my false sunflower plants. I should leave them alone to attract ladybugs back, right? I noticed less ladybugs this year in my garden than previous years (I'm in Toronto). Thanks for your insight.

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  9. They are stunting and killing my false coreopsis in coastal Massachusetts and not a lady bug in sight. Also, spraying them with the hose does not dislodge them.

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  10. i have been infested with aphids for some years and have tried everything to rid my shrubs and flowers, even purchased 50,000 ladybugs which left my yard immediately. they kill all my plants, flowers etc and have been such a burden

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  11. Each pest preys on a specific type of plant, and that's why some of their names are based on them. Aphids are among those insects that are destructive to crops and garden plants. Thank goodness super lady bugs are there to eliminate them!

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