Scottish Rock Garden Club Forum
Specific Families and Genera => Ferns => Topic started by: annew on October 31, 2011, 09:00:29 AM
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We have a new pest in our ferns. Some of our polypods started to shed new fronds, and close inspection has revealed a very tiny grub that has eaten a channel up from the base of the stipe and then pupated at the top, about 2 or 3 cm up from the base. The tiny hole filled with frass whereby the egg was inserted can also be seen under magnification, usually about 1cm up from the base of the stipe. I've consulted with a former national collection holder who says that several collections now have it, and that it might be Australian fern weevil. He also says that it might also infest polystichums and Asplenium scolopendriums. With these types, individual fronds will wilt and die.
Please keep a close eye on your polypods and if they start losing fronds when they shouldn't be (ie NOW!) you need to take action.
Remove and destroy fallen fronds which might contain pupae, and (if you are not organic) drench with Provado. The expert says this regime has cut his once big problem down to just a few fronds lost. He also dusts the plants with ant powder.
It would seem that the best husbandry option would also be to allow the old fronds to shed naturally in the summer then collect and destroy them, rather that cutting the old fronds off before the new ones emerge, as this latter option would leave the stipe bases in situ, which may contain beasties.
I hope I haven't inadvertently spread this problem to anyone who has had polypods from me. Please email me if you think this is so.
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Very alarming Anne and thanks for sharing the information. Will you keep one until it pupates and hatches in the spring?
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I've been round and collected up all the shed fronds. I'm going to cut off the tops and store the frond bases in a container with a mesh lid in my garage over winter and see what comes out.
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Must check my three ferns tomorrow