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Blue Porterweed, Stachytarpheta urticifolia, With Piles of “Dirt” Along Stems

These piles of dirt are accumulated frass and silk webbing from a caterpillar, [Pyralidae: Penthesilea
difficilis],  tunneling inside the stem (photo with flower and frass by Stephen Brown, UF|IFAS Extension Lee Co.)There isn’t too much one can do with pesticides since the plants are used to attract butterflies and bees. About the only thing to do is be diligent and prune the affected stems before the caterpillar (in the banner picture) changes into a moth (see image below)  and procreates more offspring that will damage more stems. Cut the stems into 2 inch long fragments to kill larvae.  I’m not sure if the native porterweed is affected. And its doubtful that the porterweed will die from the damage. Its more of an aesthetic distraction.
See info on the different porterweed species here:
http://blogs.ifas.ufl.edu/collierco/files/2019/10/porterweed-species-Cute-Plants-that-Take-Over-Your-Yard-blog-Doug-C.pdf

 

 

 

2 Comments on “Blue Porterweed, Stachytarpheta urticifolia, With Piles of “Dirt” Along Stems

  1. i have a big infestation of this on my native porter weed. Didn’t really notice it until it has really devasted my plants an is spreading. It is overwhelming the plants. The caterpiller appears to burrow down inside the stem and then the branch dies. It may be too late for me to control it by just cutting the infected stems out. How do I get these insects under control. Do I need to remove all the porter weed and let the ground remain dormant for a while? I have the infestation in my backyard, but have porterweed in the front also, and I observed early signs of infestation in the front. Would appreciate your advice. So glad you’ve identified my problem.

  2. Thanks for your info–i didn’t realize this was the problem with my porterweed until the plants were quite infected with the caterpillars. I’ve cut the stems as you suggest…but continually find many I’ve missed. The infestation is pretty established. What’s the best course of action? I’ve cut back the porterweed substantially, but probably the moths are around and will continue to infect. If I remove the porterweed completely…and start over, must I continually (almost daily) check the plants for infestation? I’ve had the plants for a few years before the problem occurred.

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