I've just noticed a few of those dreaded Fungus gnats on the top of my compost,its not a big problem yet as theres only a few but i want to eradicate them before it gets out of hand.After doing a bit of research on here i know the larvae are just under the soil and can eat/damage the fine roots but the adult flies don't do any real damage to your plants.So i was wondering what is the best plan of action i should take?

Buy some "Gnat off" and just mix 1ml/ltr when i water them? (is it any good?)

or

Cover compost with washed Sharp sand or Perlite?

I will be buying some yellow sticky traps from Q&B tomorrow anyway to keep the adult numbers down.I just need some advice as to which of the above options i should do.
Thanks in advance!

Stcky traps and sand should do it Amnesia

They've just appeared in my grow for the first time this week (week 8 flower) - wth c4 weeks to go I wonder if I should do something Just saw above about the little scamps nibbling the fine feeder roots don't want that

Sorry to butt in on your thread man but I jumped when I read your post I was all - should I worry Little shites ain't having at my lovely Lot#5 Should I be concerned this late in the grow or just research it for next time ?

As above Arbuscule mate, traps for the adults and sand to prevent the larvae emerging from the medium, if your quick enough you will break the life cycle get rid of the wee buggers

Nice one Hughie

Thankyou Hughie,a lot cheaper too than £20 for Gnat off!
I don't think they are really much of a problem to the plants or roots unless you have an infestation,So i would not worry about it Arbuscule as you only have just noticed them!.I would do the same as me though and treat the pests early.
A half inch of sharp sand on top of the pots and some sticky yellow traps it is then!

I've also just read on here that if you want to know how bad your infestation is just get a half of potatoe peeled and put it in the top of the soil,the larvae and flies will be drawn to it.Check underneath a few hours later and you'll see them there.

Cheers Amnesia Reckon I'll get some sand - thanks

Nice tip Amnesia........

I tried gnat off for a while (3+ weeks) and it didnt really ever clear them up fully so not sure its worth the 20 squid.

Fungus gnat larvae don't do much damage to larger plants, but they can be very damaging to newly rooted cuttings - it's with your seedlings and in propagation areas you really have to watch the buggers.

They can be controlled biologically, with Hypoaspis, but they come back anyway. If you clean up well between crops and don't leave any old compost around they shouldn't get out of hand. They love moist peat.

I forgot to ask,should i wash the sharp sand through first?,also it might sound like a stupid question but do i just leave the sand in the pots then until harvest time?
If this sand trick really works then would it be a good idea to put the sand on top on your final re-pot in future as a precaution to stop any larvae from hatching?
(obviously it would be no good doing it in earlier pots as you would get too much sand mixed in with the soil on pot-ups!)
I'm in my second week of flowering by the way.

How about a layer of hydroton on top of the pots and hit them with the Henry every day till they're gone.

I take it that's clay pebbles? ,excuse me for being dumb but wtf is "Henry"
If they do work that would be excellent as you can put a layer on each re-pot,Is this a tried and tested method then?

Hydroleca is an excellent topping, and will help keep down the sciarid flies. It also stops the soil drying out so much, etc.

I re-use it about 3 times.

Henry is the hoover I think, and scribbles advice is really good - I just squash them if I see them, but I bet that works better.

I had success in the past with a combination of sticky traps to get the adults, and extending the gap between waterings by a extra day for a couple of waterings so to as to dry out the larvae.

I'll try these clay pebbles then,is it okay just to wash them in normal tap water before use?
I water/feed the plants every 3 days on a wet/dry cycle,on the third day the pots are bone dry and very light so i can't really leave them longer as i don't want to stress them too much.
I've just had a real good look after shaking the plants and tapping the surface of the soil and i would guess theres only about 4 in each pot at the moment but i want to get on top of this before it gets out of hand.

That's what I do.

Well i've got the Hydroton clay pebbles and the sticky fly traps as recommended,the fly traps are on top of the pots now.
Just one thing before i put the pebbles on..
Should i wash them before i put them on top?
Thanks again.

yes you wash them in water before use m8,good luck

Sorted!
After putting the pebbles down and the sticky traps problem solved,i only had a few flies anyway so those few got stuck to the tape.I've shaken the plants and moved the pebbles around and i can't even find one now!
I'll be leaving the tape there until harvest.
I'd recommend anyone with compost grows to do this as prevention is better than cure,All my future grows will have a layer of these pebbles on top and fly traps just in case!
Thankyou very much to all that advised!

washed sand done it for me ... as mentioned above get your self to b&q or wickes matey good luck wif em was a nightmare when i had them..

Ant powder, quick puff of that on the top of your pots will soon see them off, next time they land they'll be covered in Permethrin.

Hi,

I ran off with this problem as well.

What i did was to put on top of the compost around 2/3mm of some dry neem that to use on mixing of the soil (in portuguese/spanish is called torta de neem).

That way i killed two rabbits in a stroke: the neem on top of the earth prevented the damn gnats to lay eggs and when i watered the neem entered the earth and killed the little bastards that were on the earth. I waited for the compost to get really dry (yes some plants started to show signs that needed water) and i rid of all of the bugs in less than one week and half!

My method is fast but can be messy for the plants.

Hope that it can help someone!

i have just found 3 gnats which i killed by hand in my grow, 1 got away from me and cant find im! so i think i will be getting some sand from bnq tom and some fly traps to rid the lil fekers, just wondering what sand i would ask for in bnq>?

Sharp sand.

I always use a product called Mosquito Dunks; they are very effective against gnats. They contain a bacillum (no chemicals) that attacks the gnat larvae which are eating the roots of your plants. The gnats don't do much harm, but the larvae can kill your plants. I recently got re-infested from some clones a friend gave me. I immediately ran to the garden store for Mosquito Dunks because they REALLY WORK! I fill 5 gal. buckets and let them sit overnight to expell chlorine, then add a dunk to each bucket. If I want to feed I pour off into gallons to measure the nutes, otherwise just water from the bucket. when I refill the bucket I remove the Dunk for overnight, then put it back the next AM. Sometimes I crumble them up and mix a little into the soil with no harm. Be careful of another product that is chemical and shaped like small, black fish. You don't want those. The Mosquito Dunks are light brown and doughnut-shaped. Use them for a while and your problem is over.

Bacillus thuringiensis not for some LINK , bottom air movement sticky traps and clap hands for me , good luck .

thanks all think i will go with the sharp sand and fly traps as seems the least drastic option with good results :-) i am just wondering where 1 of my plants is in flower and the others in veg? shall i fill all the pots with sharp sand on the top or wait untill the end of the week untill my vegging plants go into their final 7.5L pots then fill them with sharp sand 1/2 inch on top?

Ive used sticky traps and sand,but be careful which sand u get,u want it from a nursery,not construction type.

really! surely sharp sand is sharp sand where u buy it from bnq or haskins? i was going to get some from bnq tom as i am potting em all up tom now as well due with loads of roots coming through bottom. Will this be ok from bnq then or shall i have to hike further to haskins?

bnq have got sharp sand and natural sharp sand, both the same price, is this stuff even ok to use as chars says be careful which sand u get,u want it from a nursery,not construction type.???

I wouldn't have thought it mattered which sand you use tbh

However if that doesn't work or is too much hassle I can recommend ant powder.Just sprinkle it onto the top of your compost and water in...couple of doses a week for a couple of weeks has killed all of my fungus gnats.

ant powder?? thats poisonous isnt it? my plant is nearly 5 weeks into flower will it be ok feeding the plant that???

Its certainly poisonous to fungus gnats

As I understand it the poison isn't absorbed by the plant and therefore can't be transfered through smoking.I'm not an expert by any means but I have been reliably informed its safe from people who really know their stuff so thats good enough for me.

sounds like a plan as i have a bottle under the sink all ready! i really just dont feel right about putting it in the compost lmao u 100% sure it wont damage the plants or me as i might do it in a bit if the case

Heya , i would not only be concerned for youre safety but i would also think others issues would be involved for anyone one to advise you use unknown or any poison .

right man conflictions thats enough to put me off ant poison im affraid, going to go with the plain and simple sharp sand, atleast it wont kill me thanks all

I've just lost 5 seedlings to these gnats. £40 down.
They all looked fine, then simply dropped dead over a few hours, being left with no root at all. There's a few gnats flitting around, & I saw a larvae.

I've had them before in my flower room, but with traps up, not much damage seems to be happening... not sure now though, maybe my crop could be suffering.

Stuck another trap up.

I've cut some sticky traps to shape & placed them on top of my new seedling's pots, so the flies will immediately stick upon leaving bug stage & taking wing for the first time. I feel cruel, but the seedlings don't have a chance otherwise.

I reckon the bugs are in the compost already, straight from the garden shop. Is that likely? Should I throw my big bags of compost away I wonder?
I'm gonna get some sharp sand also... hoping it's ok from builders shop as opposed to garden shop.

Cheers for the info.

Hi Muds,sorry to hear you lost your girls to those dreaded gnats.you are right in what you say about them being in the bag already in the garden centre,when you water the plants and put them in your warm growroom it is a perfect enviroment for the larvae to hatch.I've heard some people microwave their compost first to kill any larvae but i would not recommend this as you may also be killing "good" bacteria!.
The sharp sand and fly traps definately works as the sand stops the adults laying the larvae and it also stops any larvae coming up through the soil by shredding them as they try and get through the sand,make sure you use sharp sand though as builders sand is too smooth and also contains unwanted minerals and salts.
Water the girls gently with a fine rose so you disturb the sand as little as possible.When you repot just tip out the sand first,repot and put fresh sand on top.

They don't like the smell of cinnamon I have tried it get a litre of water add a table spoon of cinnamon simmer for 15 min's stiring occasionally add a little gardener's soap or a few drop's of washing up liquid strain the liquid off and remove the sludge and disgard put liquid in a spray bottle and 15 - 30 min's after watering and the water/feed has been absorbed spray the top of the compost and spray some round the driptray, not ideal but if your mid grow / flower it does help the gnat off stuff you have to use several time's as it kill's the grub's
Also as gramp's has said yellow sticky trap's round the base of your pot's and a bowl of apple cider vinigar some where in the grow room

Given Permethrin's low mammalian toxicity and the fact that is is used to impregnate clothing to keep insects off and has been used as a treatment for head lice I wouldn't be too concerned if it's used correctly.

Hi all just got some sharp sand from bq this mite be a stupid question but is it already washed? if not wots the best way 2 wash it??

Heya , i was referring advice on Ant Powder not a specific ingredient .

If you use ordinary sand it's full of salts that get washed into your compost every time you water. you want children's play sand, Argos do it.

The covering you put on the top, sand, clay balls, etc. stops the fungus that the young ones feed on from forming just under the surface of the compost.

The active ingredient in most ant powder is Permethrin

Heya felix , im sorry but leaving a sweeping statements on poisons on not even a brand name is wrong , i can name four uk top of my head as should anybody who intends to use it , well at mimimum the one there using on a plant for consumptions or anything else , the americans have a nice one coming out , check it out .

I do agree it's best to give specifics where possible , got any information on the new product coming out in the States ?

Heya Felix , i forget the make without some un-archive-ng , but im sure its one of the major possible nippon or more than likely Bait station , but of that products alone THREE active ingredient was something simlar to the now called diatom , ie kelp cells etc , my reading didnt go as to micro effect level .

anyone know if mixing some detergent with tobacco actually works without harming the plants?, or letting the soil dry out a good bit?

We use Diatomaceous Earth for flea and mite control on our animals and I've also used it very effectively against crawling insects but did try dusting some around the tops of my plants to control fungus gnats but I think in my conditions the top of the soil was making the powder slightly damp which may have hindered it's effectiveness as the gnats seemed largely unbothered by it . Still it works wonders on our cats and we haven't seen any fleas on them all year so there must be something to it

@vardy,

Not sure on the detergent and tobacco mix but letting the compost dry out properly between waterings is always good practice