It sounds like you may have seedlings of Blue River II. Do you have a photograph which you can post?
I found three or four Blue River II seedpods which were filled with dust but there was always a hole drilled in the side of the seedpod. Some of my BR2 seedpods were also compromised by the Hibiscus Seed Beetle (Althaeus hibisci) but in that case the seeds were mature but had holes drilled in to seeds where the Beetle emerged. For reasons unknown I only found the Hibiscus Seed Beetle early in the season and the problem did not reoccur and I only lost a few seeds. Many of my hardy Hibiscus have a lot of Hibiscus coccineus DNA in their ancestry and Hibiscus Seed Beetle doesn’t appear to like the taste.
I produced a large number of BR2 seedpods this summer, both hybrid and self pollinated, and with the exception of some off-the-wall crosses and the three or four dried out seedpods mentioned above I had a bumper crop of seeds.
Two insects were identified:
A weevil, Conotrachelus fissinguis (Coleoptera, Curculionidae) and a bruchid beetle, Althaeus hibisci (Coleoptera, Bruchidae).
The spelling of Conotrachelus fissinguis used in the above paper is not the prevalent form used across the Internet. The more common spelling is Conotrachelus fissunguis where second “i” in the species name is replaced with a “u”. In taxonomy it is not uncommon to find variations in spelling depending on the source but there is also the possibility that an error exists in above paper. The following is a picture of C. fissunguis.
"The weevil Conotrachelus fissunguis larvae eats the seeds as they develop and then bores a hole through the pod and drops to the ground to continue development."
As I am all too familiar with Althaeus hibisci and know you don’t have that problem, therefore I would move Conotrachelus fissunguis to the top of the suspect list. Did you find a hole in the seedpods?
The presence of a hole in so many of the failed pods strongly supports the theory that Conotrachelus fissunguis is your problem. What I don’t know is how to deal with the problem. Any broad spectrum insecticide is going to discourage pollinators and you may have to resort to hand pollination.
One insecticide which may work is Bayer Advanced™ 12 Month Tree & Shrub Protect & Feed. This product is the replacement for the now band nicotine based product Black Leaf 40 and contains a synthetic nicotine derivative by the name of Imidacloprid http://en.wikipedia.org/wiki/Imidacloprid
Basically Imidacloprid makes your Hibiscus taste bad. I user this insecticide to good effect this summer on my Hibiscus mutabilis which had several insect problems. As Hibiscus are fast growing I would treat the plants once a month and not once a year as the manufactures instructions recommend. I found monthly applications necessary for my Hibiscus mutabilis because new leaves did not appear to absorb the Imidacloprid without a new application. Bayer also uses Imidacloprid in a faster acting rose and flower spray.
If you have several Hibiscus plants, try treating some and see of the product works for you. You seed predation problem makes mine look trivial. I am more concerned about preventing the spread of Althaeus hibisci.
I found this Canadian paper on Hibiscus moscheutos which addresses insect predation.
I don't use any chemicals(I am too cheap and allergic) except for spot treating for fire ants when I get nuclear fission mad after not paying attention where I put my feet or tiny hiney. I think I will just leave the hibs alone. They flowered great and I don't need the seeds. Maybe I will get some lucky seeds in 2011. If I want more plants their cuttings root as easy as anything.
Hi Larry, I have plenty of white Hibiscus seeds if you would like some. I have shared them with a couple of other interested DGers. I didn't know the name of it but when Michael mentioned Blue River II - I looked it up and indeed it is the Hardy I have in my backyard. If you are interested, Dmail your address and I can send you some.
Below are two quotes from the papers I referenced above pertaining to the egg laying habits of the weevil C. fissunguis:
”Adult weevils lay their eggs inside the young seed capsule. The larvae consume several to many seeds as they develop, while the fruit continues to mature. Eventually each larva bores a hole of 2 mm in diameter in the fruit wall to exit from the capsule. The larvae then drop to the ground and begin pupation in early September (Weiss and Dickerson, 1919).”
”The other beetle that is found to be destructive to H. moscheutos' seeds is the
weevil C. fissunguis. Apparently the adults feed on the bases of the petals and deposit their eggs within the maturing capsule. The larvae feed on the seed contents and locule wall and at dehiscence drop to the ground. The larvae pupate beneath the soil surface (Blanchard, 1976).”
I am speculating that if the young seed capsules could be protected for a few weeks, while it is still tender, from the C. fissunguis weevil, seeds could be harvested successfully.
One possible solution would be the insecticide Bayer Advanced Dual Action Rose & Flower Insect Killer which is available in most box stores for about $5.00 in a spray bottle. Another possibility is some of the organically approved soaps, oils, hot pepper spray or garlic. Which ever method is used, the treated seed capsule should be tagged for future identification. Once the seed capsule walls become thick enough I suspect it will be safe. Perhaps a simple and inexpensive solution can be found?
This spring i wrapped my castor bean seeds in the toe part of nylons to keep the seeds from falling to the ground where my dogs play.. I'm wondering if you put nylon over the hibiscus seed pod if it would keep the bugs out??
Gail thanks for your generous offer. I currently have enough plants if they make it thru our hopefully mild winter. They should, they made it thru last winter, some in 16 oz stryo cups and some in 1 gal pots. I have some seeds left over from 2007 or '08 surely some of the 3 YO seeds will germinate. I also have a couple of rooted cuttings in the geenhouse. I should be ok.