Scottish Rock Garden Club Forum
Cultivation => Cultivation Problems => Topic started by: John85 on August 15, 2011, 11:31:53 AM
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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.
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I'm having similar problems, John.... no idea what the problem is.... it has been rather wet here though.
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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.
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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?
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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
:)
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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.
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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! :-\
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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.
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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. >:(
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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...
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Thank you for telling me Arisema but I used one with Pymethrine
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Can I add that not many of my cuttings have rooted this year :'(
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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?
??? ??? ??? ??? ???
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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!
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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.
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maggie they sound like root aphids,i dont think theres any way of knowing your plant has them really, i suppose spray with a systemic if your are worried,its what i am going to do.Mine were in my normal soil as well not compost,these were seed grown by me.
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Dave, I don't think you can buy any sort of systemic in Canada.
It seems that anything and everything that worked at killing pests has been banned. :(
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Assuming we're talking about the same things, root aphis come in white or creamy/yellow colours, with a sort of powdery substance around them. That's the case here anyway. All the ones I find are the yellow sort and they are usually on potted plants and almost always on Primulaceae, sometimes on Saxifragaceae. I unpotted a plant of Primula clarkei last week and found dozens of them on the stronger roots. They come away easily - I used the tip of a thin metal label - and seem to leave nothing behind though what their eggs might look like, I don't know. I always find them on the outside roots, where the roots are touching the pots, not within the root mass, which makes them easy enough to dispose off.
My course of action nowadays is to sprinkle a little suSCon green around the roots and either plant out or repot. I've never found them on a plant previously infested but treated in this way.
It surprises me that they would attack dandelions. Most nasties go for the most rare/difficult/treasured plants one has. >:(
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Lesley, the dandelions I pulled up mostly had very big roots, like small parsnips.
The critters were wall to wall around the roots, starting from the top with less towards the bottom.
So close together they were almost overlapping.
I just used my fingers and squished them.
The dandelions pulled up easily. Only time I have had weeds pull up so easily was in spring when the ground has just thawed.
We had had a great deal of rain during spring and early summer but the dandelions that were infested were in one small area, even the tiny ones had some of these things on them.
3 feet away, there was no sign of any on the dandelions I pulled up.
Haven't seen one since and hope I never do.
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I also have had what seems to be root aphids (white) on one year old dandelion roots. Only a couple dozen or so per plant, though.
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Lesley,
What is suscon green,please?What is the active substance?
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John it's a rather nasty stuff in tiny green balls and with an unpleasant smell. I'll leave you to look up the active ingredient on the internet but it is dangerous if not used correctly and we are not permitted to purchase it now except with a qualified agricultural contractor's certificate. It is spelt suSCon green (I think) and I believe it is a german product. It is absolutely lethal against underground things like root aphis and vine weevil grubs and also against narcissus fly. I always put a pinch among new daff bulbs either in the ground or in pots of Narcissus or Galanthus. I also always wash my hands after using it.
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To the best of my knowledge, 'suSCon green' is not available to amateur gardeners in the UK & probably also the EU.
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In case anyone is interested in seeing what these things look like.
Just pulled up a couple of dandelions.
Not as many as there were on others but enough to see.
It seems that the dandelions that have these aphids come out of the ground easily when you pull.
A few fell off while I was taking pics and some tiny red ants scooped them up and carried them off.
I kid you not.
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Those don't look like mine at all Helen. Mine have no visible legs or feelers, just a little yellow body covered in a powdery substance. I'll take a picture next time I see some. They are very squishable though.
I'm not surprised Gerry about suSCon Green in the UK. It's no longer available here either to amateur gardeners and I'm hoarding my remaining supply and only using it onthis susceptible to certain pests, like Narcissus fly. In 1993 when I was last in the UK and brought back plants, I had to have them dipped before they came home but the substances which our MAF required them to be dipped in, were no longer permitted under EU regulations. So they came home undipped and had to go through the process immediately I arrived in Auckland. Best not discuss the results of that exercise. My blood still boils.
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Helen's aphids do look just like mine did.
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So I wonder what mine are then? Maybe mealy bugs? I'll photograph ASAP but I don't want to go unpotting primulas to find some. :-\
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Helen,
I wonder if the ants were taking the aphids away to eat them or to breed and "milk" them as they do with the foliage aphids to get the honey dew.
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John, I am pretty sure the ants are farming the aphids.
Am now paranoid that the aphids might develop a liking for clematis roots.
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With a lot of toxic chemicals going off the shelf I have been using more and more often organic sprays like the chillie and garlic sprays bought at most garden centres. It really works. I had drench some pots that had root aphids. I even tried it on some ants and it works!
Also neem oils are good as a contact insecticide Ive used it on lace bugs and great for killing mites.
cheers