Problems with dwarf dianthus

[John85]

My dwarf dianthus are all dying, going yellow on the outside of the"hummock".They are not difficult sp(several cv of grationapolitanus or even squarrosus.....).I have grown them for many years without problems  certainly not during the summer and here we had not a particular wet one.
They are grown in a gritty mixture in the rock garden.
Any idea what it could be?I haven't seen any bugs,just a few ants.

[Maggi Young]

I'm having similar problems, John.... no idea what the problem is.... it has been rather wet here though.

[Lesley Cox]

Unless it's a problem you can soon identify and successfully treat, the obvious plan would be to take cuttings from each ASAP and so have young ones coming on if the worst happens.

[John85]

I have already done that Lesley as I make cuttings to give away to friends.
Unfortunately I am not lucky with cuttings of the very very dwarf forms.For those layering is easier but that is impossible now as the disease starts from the foliage close to the soil.
I have used insecticide powder to control the ants population as this year the invasion was exceptional.Could it be that it is phytotoxic?
Has anyone experimented the same thing?

[katijah2]

Might Vine Weevil be the culprit?

Check the roots of one yellowing plant, if its eaten away its the VW or colonies of Ants possibly John

 

[John85]

Two days ago i saw some tiny mushrooms all around the dying plants.Not exactly the place where one 'd expect them:the soil in the rock garden is stony and well drained.They lasted only a few hours as a big slug was having them for dinner,so it could easily been unspotted.
I wonder  if that is the reason of the problem or if the fungi are just feeding on the dying roots.

[Maggi Young]

Two days ago i saw some tiny mushrooms all around the dying plants.Not exactly the place where one 'd expect them:the soil in the rock garden is stony and well drained.They lasted only a few hours as a big slug was having them for dinner,so it could easily been unspotted.
I wonder  if that is the reason of the problem or if the fungi are just feeding on the dying roots.

Hmmmm..... the mystery deepens! 

[Panu]

I have had small fungi in my rock garden, but I donīt believe they are the problem. This year has been awful with ants though, they have killed several small Dianthus and some other species like Saponaria pumilio and small Acaena fissistipula.

[daveyp1970]

Can i just add i have pulled a weak and sad dianthus out of the ground and because i have ants destroys a few things thought it was them but on inspection of the roots,discovered them covered in aphids.GRRRRRRRRRR.

[arisaema]

Could it be that it is phytotoxic?

Don't know what sort of ant poison you used, but the borax based ones could probably be phytotoxic...

[John85]

Thank you for telling me Arisema but I used one with Pymethrine

[mark smyth]

Can I add that not many of my cuttings have rooted this year 

[maggiepie]

Dave, I didn't realize aphids could be on roots of plants but a few weeks ago I was pulling up dandelions, which btw were pulling up easily and noticed there were aphid like critters almost covering the root.
Is it common for aphids to be underground?
 

[John85]

Hello Helen
Not as common as on the foliage but here you see them more often than a few years ago.It is mainly because of the nature of the potting compost:as a peat substitute,bark is often used in the mixture.
Roots aphids seem to like the airy structure and in some nurseries they have to spray regulary with a systemic insecticide to control the problem.
Bought six alpines at a plant fair,four had aphids on the roots!Washed the"soil" out and repotted them in my own home made compost and.... put them in quarantine!

[maggiepie]

John, I have never seen these things before and the soil in the part of the garden where I found them is mostly just clay amended with black earth and some compost.
The dandelions were growing in amongst my atragene clematis which were all grown from seed.
I hope the little horrors don't get on my clematis roots.
Am not sure they were even aphids but were the right size for aphids and were white.