Root destroying insects

My flowers are wilting due to small black insects. When I dig them up there are no roots left. They dont eat the flowers or leaves. Does anyone know what they are and how to get rid of them.

A description of the insects would help - size, number of legs, speedy or slow? Also a good poke around to see if there is anything else there because often creatures (like woodlice) move in after something else has caused the damage and then you waste time trying to eliminate the wrong beastie. 

Sue31 wrote (see)

My flowers are wilting due to small black insects. When I dig them up there are no roots left. They dont eat the flowers or leaves. Does anyone know what they are and how to get rid of them.

It isn't ants is it?-how do you know it is the insects that cause the damage-I think we need a bit more info-are they just on the roots?

Is it the insects eating the roots or is it their grubs? A common cause of root destruction is vine weevils. which look like little black beetles. Their curved, whiteish grubs do the damage but you may see the adults, which only eat the uppper part of the plant. You can buy stuff like Provado to kill the grubs and you have to pick off the adults by hand, preferably at night. Another common cause of root destruction can be ants, as sotongeoff has pointed out, but I'm sure you'd haved recognised them.

Vine weevils are a horrible pest and you sometimes have to  be quite persistent to get rid of them. They particularly like the soil in pots, because it is easy for them to dig down in it to lay their eggs. Hope this helps.

The insects look like small flies. They dont cling to the stems like black fly but seem to live in the soil under the plants leaves. When disturbed, they fly a little around the soil but dont leave the plant.

That sounds like fungus gnats - annoying, but they won't be killing your plants.  

What sort of plants are we talking about, where are they and what are they growing in?

We discussed fungus gnats yesterday and agree they are a nuisance not a pest.

If something is eating the roots they are not guilty

I have flowers in pots with compost. The pansies and violas are mainly being targeted although I have found them in other flowers. Whenever I find a plant that has gone limp, I find the flies there. The healthy flowers dont have them. Also all the limp flowers have roots gone.

Have you tipped one of  the pots out?-this is sounding more and more like vine weevil grub damage-is it fresh compost?

I start with fresh compost. If the pot is badly damaged, I tip the compost out and start again with fresh compost and new plants. I haven't found any other insects other than flies and  I wouldn't be able to pick the insects off as they fly around too quickly and are too small. They have also spread from the front garden to the back and as I mentioned all damaged plants have the flies but the healthy ones dont.

Well you need to tip one of the pots out and inspect for something nibbling the roots-I still have very strong doubts that the flies you are seeing are doing that damage.

I agree with Geoff - fungus gnats, which are the tiny flies you're seeing, do not eat roots.

However, they love very damp, even soggy, soil - I wonder if your plants are simply rotting in the wet? Do all your pots have adequate drainage holes?

I agree that the gnats are likely to be attracted by the decomposing vegetation of your damaged plants. Have you tried going through the roots and looking for grubs? Sorry if this seems to be treating you like an idiot..

How long have these pansies and violas been in their pots?

I planted them this spring. The pots have drainage holes and aren't waterlogged. I have often changed the soil and haven't found grubs. Not all plants are affected and I often have healthy plants in the same pot. The sick plants just wilt, similar to a plant short of water ( which they aren't) and have roots missing. Maybe the grubs are very small and I haven't noticed them. Thanks for everyones help anyway

There are treatments for Fungus gnats (Sciarid flies). In large numbers the tiny soil living grubs could damage plant roots, but they have to be in large numbers. Also try putting a good deep layer of grit over the compost. This stops them from laying eggs.