PlantAdvice.co.uk

Hi - over the years I have had problems with keeping plants indoors - I've hadsome magnificent specimens but have ended up throwing them away as the compost has become infested with some horrid insect. At first you only notice them when you water the plant - as the water starts to settle the compost seems to come alive with these tiny squirming, jumping white insects (they are about the size of a thrip). They seem to breed very quickly and soon you can see them even without watering the plant - they jump if you try to touch them.

What are these and how do I get rid of them without getting rid of the plant?

At the moment they have just started to appear on my tomato plants (which I've had to keep indoors cos we keep having nights below 5 centigrade). I need to treat these but am concious that I will be eating the tomatoes at some point so want something that is organic if possible, if not, safe at least!

Many thanks,

Hello Claire,

I would be interested to hear what other people think, but I think you are describing Sciarid Fly, Common name: Fungus Gnat. It might be that the compost is slightly too damp. If you want to control sciarid fly organically, visit your garden centre and ask about sticky yellow traps that can be hung above affected plants. I seem to remember that the yellow colour attracts the adult flies and they get stuck to the trap. The adult flies themselves do no damage, it is their larvae that eat young roots. Catch the adults and you will deal with the larvae!

Hope this helps,

Regards, George.

thanks for your reply George. I looked up the insect you suggested but don't think it is that as they are black whereas the pesky things I have found are white. The search did lead me to what I think they are though. Here's what the RHS had to say:

Springtails (usually Onychiurus species) in pot plantsPlants affected
Many pot plants, especially those grown in peat, coir or other types of soil-less compost.

Symptoms
Small wingless insects, up to 2mm long and often white, crawl among the compost of pot plants. They are most noticeable after watering when they come up onto the surface before burrowing back in the compost, or they may be flushed out through the drainage holes and be seen floating on the drainage water.

Other white insects of similar size found among the roots of pot plants are likely to be root mealybugs. That sap-feeding type of pest is relatively immobile in the soil compared with the much more active springtails. The latter also has a pair of antennae visible on the insect's head, whereas those on mealybugs are microscopic.

Cause
These insects are springtails, so-named because many species (not Onychiurus spp.) have a forked structure folded under their abdomen; when flicked out it propels the insect into the air and helps the creature escape predators or adverse conditions. Many species of springtail of various colours occur in garden soil but the types most frequently found in potting compost are white Onychiurus species.

Control
None is necessary. These are harmless creatures that feed on fungal growth and decaying plant material. They are dependent on damp conditions and so will not spread away from pot plants or become a nuisance in the home.

Another site gave the following advice for controlling them:

Immediate action

Natural treatments

Methylated spirit application ('soap-spirit') Mix about a quarter to half an ounce of methylated spirit and a similar quantity of soap or washing-up liquid into a quart of water, agitate to foam and apply the foam directly to the predator-infested parts. Repeat once or twice daily as required, and increase the concentration of methylated spirit if necessary - it's doubtful that you will damage the plant by the time the predators are dealt with.

Tobacco maceration/infusion spray Soak an ounce of tobacco (preferably pipe tobacco or similar; cigarettes contain too much saltpetre, etc.) in a gallon of water overnight, Strain, etc.

An infusion made by boiling is stronger, but smells awful in the kitchen! Dispose of the tobacco residue, don't put it in the compost.


Thanks for all your help!