Black-Eyed Susan Leaf Damage

The damage to my black-eye susans (rudbeckia species)is worse than ever this year and I’ve even noticed that a big patch of them has not come back. Now it certainly wasn’t because of the cold winter we had–because we had one of the mildest winters ever.  So I have to believe that it is because of this pest that’s attacking them.

Despite my best efforts, I’ve not been able to get even another glimpse of the nasty little bug, but some further research, and a conversation with the one of my colleagues from the garden center where I used to work has me now convinced more than ever that this is indeed an insect and not a fungus.  I just do not know why more folks haven’t caught onto this.

This post from the University of Connecticut IPM program, describing the four-lined plant bug and the damage it causes, has not only nailed down the problem exactly, but it has made me wonder if I haven’t misidentified the pest somehow and if I don’t have four-lined plant bugs on the black-eyed susans.  It scarcely matters–the result is the same–I have a hard-shelled beetle type creature that I can’t see doing so much damage to my plant that I can’t believe it.

Further, my organic controls are not really going to work all that well (thankfully, these guys only have one generation a year where I live!)  But I’m going to have to find something to stop them because I don’t find the egg masses to wipe them out early!

Here’s what UConn has to say about this bug: Feeding causes brown spots on the young foliage.  Because the spots are round and fairly uniform, many gardeners mistake it for a disease.  The insects are fast-moving and rarely seen, so most gardeners are further convinced they have a disease, not an insect on the plant.  Finally, the injured tissue may fall off the plant, further giving rise to disease like symptoms.  This is why garden centers for years have been selling gardeners fungicides to “treat” this problem.

And because the insects have one life cycle, there may even be the illusion that the fungicides work (which a true fungicide rarely does, by the way.  It can control disease, but not cure it.  FYI).

So the next time your black eyed susans look this bad, run for the insect ID book, not the fungicide.  Meanwhile, I’ll try to find those nasty overwintering eggs this autumn since chemical controls are not an option for me.

6 thoughts on “Black-Eyed Susan Leaf Damage

  1. Pat June 5, 2012 / 3:49 pm

    Glad to read this as I, too, had concluded it must be fungus or some such. Memphis never has crazy bad winters and this one was so mild we have many more spiders and everything else inside that might otherwise be controlled by a few good freezes. I’m happy to have found you.

    • gardendaze June 6, 2012 / 8:19 am

      Glad to have been of help! I just wish there were some better way to control the problem! Thanks for reading!


      • Pat Britt June 7, 2012 / 12:54 am

        I was just wondering, would Sevin Dust be helpful at this point? I also have waaay too many snails in our beds. Could they be a problem? They love basil and young zinnia plants but I don’t know how they feel about black-eyed Susans!

      • gardendaze June 7, 2012 / 8:29 am

        You could try Sevin but I hate to use anything that toxic on edibles like basil. There are a few great organics that really work on slugs and snails that are made of iron phosphate and they’re fairly easy to find. I believe the brand name is Escar-go! (cute as well as effective!) The only thing you’ll want to be wary of–and of course this is true no matter what kind of pesticide you’re using–the Escarg-go is a pellet you shake around the plants. From what I’ve heard, dogs are very attracted to the scent so you’d want to keep your pets away, if you have any.

        Let me know how you you make out, whatever you try!


  2. Becky Gammey June 15, 2012 / 2:35 pm

    I have noticed that in the middle of the black spots there appears to be a lime green color bump. kinda raised. have you ever seen this?

    • gardendaze June 15, 2012 / 2:43 pm

      I have seen this–this sort of damage is usually caused by an insect making a gall. You’ll find them on all sorts of plants from oaks to goldenrod to just about anything–your black-eyed susans! They don’t damage they plant–they’re just they’re using it as a sort of incubator. But the galls they can occasionally cause can be pretty weird looking! Thanks for reading!

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