Gnats

I always make a point of buying Sterile Germinating Mix from a reputable supplier and making sure my pots etc are cleaned with bleach before starting a new batch of seeds. I've never had a problem with Damping Off (touch wood) but almost always end up with Gnats. Grrrrrr! Where do they come from? Is it possible that the worms are lying dormant in the mix waiting for me to just add water? If so, how can I prevent them in future?

Check out the new thread I just posted on sterilizing potting mix.

Bottom watering helps keep the gnats down for me -- they like to lay eggs on moist surfaces, and when you bottom water the top layer of potting mix tends to be more on the dry side.

Some people use diatomaceous earth (teeny remains of creatures with glass "skeletons," harmless to you but cuts up little insects and their larvae), which you can find at a garden center or more cheaply (if you need big quantities) at a store selling supplies for swimming pools, since it's used in filters. You can sprinkle it on the surface, or you can make "traps" by putting it into shallow containers and keeping it moist. If you're puffing it around, be sure to wear a dust mask -- this is not something you want to take into your lungs.

With my african violets and other houseplants, I've found that I can knock back fungus gnats by adding a capful of murphy's oil soap (some use lysol) per gallon when I water.

The good news is that I think they have to be present in quite large numbers for their larvae to do significant damage to roots of seedlings or cuttings... for me, they're mostly a nuissance but don't do much harm that I can see. So it's OK if the measures that you take don't kill off every last one. (I know people have reported serious damage from fungal gnats, so I'm not saying it doesn't happen, just that they usually don't seem to be that serious a threat.)

Oh, just an added note... if you try the Murphy's or the Lysol, test it out on a few seedlings before dousing every one of them, just in case it does more harm than good for a particular type of plant.

Spraying with Neem oil will also help.

yellow sticky traps

P

A woman who works at taking care of plants in office buildings and such once told me that you can add a tsp. of clear Ammonia to a gallon of water to control Fungus Gnats. Just use this solution to water the plants. Has anyone else heard of this method? How about sand on top of the pot?

Going the "chemical way" I am sure some Systemic Granules watered in would kill anything in the soil.

Gita

Thanks for all the replies. I use the yellow sticky traps but haven't tried any of the other methods although I do have a supply of Neem, DE, Murphy's and Ammonia. I wonder if sterilizing the "sterile" germinating mix will help prevent them? A lot of people have recommended adding sand to the top of the pots but I can't see this being effective until the seedlings are of a decent size. Some of my seeds are smaller than sand grains.

I've only recently started bottom watering - previously I used to spray water with a mister. I'm surprised by how much water I have to add every couple of days.

Remember that Ammonia is also adding nitrogen, something to be aware of if you are fertilizing too; too much nitrogen can burn plants.

I doubt sterilizing "sterile" mix will stop fungus gnats. Planting in another room away from gnats that are already in other pots should prove this point but I don't know if the eggs can lay dormant in dry soil for weeks or months. More than likely they are present in your other pots and lay their eggs in any moist soil available.

I have observed that if you let a cup of water sit out around your plants (or beer for that matter) will trap a bunch of them but because they have wings, there is no way you can get them all. Sticky traps and careful watering can help reduce their numbers but it just takes one fertilized female to start the cycle all over or a new plant that has eggs or larvae in the soil.

I had been plagued by fungus gnats since last Nov. The darn things have been driving me crazy. I went through 2 pkg of the Sticky Sticks. Last week I watered with 1-2 tsp of Neem Oil mixed with 1 L/Qt. water + a couple of squirts of Dawn dishwashing soap. At the end of the day there were only a few gnats remaining. This week I watered again with the same mixture & they are all gone. What a relief. The next time I will use the Neem Oil mixture at the first sign of them.

For the cause, I'll bet you're using a lower quality mix with small pieces of bark or wood in it (price isn't always an indicator of quality ;^) ). Try mixing your own with vermiculite, peat, & perlite.

For the treatment, the easiest is also the safest. I used to have heavy gnats every winter until & found gnatrol. It's an organic biological pesticide (viral) that only affects a certain group of small flying bugs. It's the same thing as in mosquito dunks ( http://en.wikipedia.org/wiki/Bacillus_thuringiensis_israelensis). It only needs to be applied once. It only takes one or two drops for a 1 quart spray bottle and they'll soon be gone for the rest of the year.

I start my seeds off in the garage where there are no other plants growing and the mix I use is peat and vermiculite only. I purchase it from Gardeners Supply and I don't think the quality is an issue. None of my seedlings have succumbed to disease thus far. I do however have a big stash of potting mix out there and that must be where they come from. I have heard of gnatrol but have never seen it in the stores around here, although someone recommended soaking a mozzie dunk and using the water. The things we do in the cause of gardening ! LOL

This message was edited Mar 8, 2007 10:50 PM

The mosquito dunks have the same thing in 'em. They'll work fine too. Just make sure to give it a long soak.
I like the liquid form because it's quick & easy, and there's nothing to handle. You can also get it at pond/water garden supply stores. It's marketed for mosquitos too, and they sell it under another name, but it's still the same bacillus thuringiensis israelensis in liquid form.

The gnats drive me crazy, also.

I've discovered a way to catch and kill them. I noticed that they always manage to get in my yeast bread, no matter how tight I have it wrapped. So, I figured that they like yeast.

I took a plastic baggie and put about a table spoon of yeast in the bottom, then add about 1/4 cup of warm water. Once that is mixed well in the baggie, I had about a teaspoon of white sugar. Mix well, but try to keep all of the mixture in the bottom of the baggie.

I set the open baggies around my plants. Just a small opening will do, believe me the gnats will crawl right in. Wait about a day or two and inspect the baggies. You will find them with tons of gnats inside, you will be amazed.. I sneak up and zip the baggie before they can escape. Next, I just smash the little boogers. Open the baggie back up and leave it for another day.

The baggie traps last about 3 days - they work great, though. I've reduced my gnats to about zero.

Anyone else tried this? Hope it helps

Crystal

To answer the question of where they come from -- I am thinking I actually bring them into my home on fresh fruit and vegetables from the supermarket. I noticed a lot of them in late summer on the onions at my store, and I bet there are other fruits and vegetables at other times of the year.

Broots, I have the ingredients for your mixture, but I wonder if you use them on seedlings...how small a plant could I use this mixture on?

Suzy

I heard a layer of sand will keep larvae from escaping as adults, and as soon as the adults die (which they do quickly - short life span) your problem is solved. Not sure how thick it has to be... I seem to remember 1/4", which may be a bit deep for flats.

edited to fix typo

This message was edited Mar 20, 2007 1:03 PM

Crystal - the yeast mix sounds interesting. I may give it a try.

I;m a little particular about buying my fruit and veg. If I see fruit flies hovering over them at the supermarket I won;t buy them. I think because it makes me feel like the produce is over-ripe and that creeps me out.

I;ve read recommendations in the pasta about using fine horticultural sand on the top of the plants but I don;t think I;m game enough to use it on my delicate seedlings. Maybe once they;ve matured a little more though.

(Please excuse the semi-colon in my typing - the apostrophe on my keyboard has stopped working!)

Suzy I don't know how small a plant you can use the Neem oil mix on but if I get them again, I will certainly try it on a couple of seedlings. I would gladly lose a couple of seedlings in the process of eliminating fungus gnats.

Here in the South, gnats and mosquitos are just part of life. We always have a can of Off or Deep Woods mosquito repellant sitting next to the door, you don't dare go outside without it during the late spring and summer. The last several winters have been very mild here in Ga. and they just seem to get worse each year as a result.
-Greg

Just for th record, I have been trying Murphys Oil for a couple of weeks with no results. Until then, I always used H30 - no dampening off, but plenty of gnats. Last night I broke down and bought some neem. I am using it this morning. The gnats are driving me crazy.

I didn't trying the ammonia because I was worried that it would be too strong.

Pennefeather, Let us know how it works.

Did you use the Dawn, too? (referencing Broots post above) I was just wondering if it was the Neem of the Dawn or the combination.

Suzy

Actually Suzy, I put some more Murphy's in it, since I have it sitting in my plant room. I don't use Dawn.

I should know if it is working in about a week, if not less.

pennefeather I sure hope that you get rid of your fungus gnats. They sure can drive you crazy. My sister was having a problem with them so I told her about the Neem & Dawn & she has tried it & it seems to be working well. It does take more than one application but you usually see a decline within a week, actually it only takes overnight for me. I will be watching to see if the Murphy's works. I know that Murphy's is mentioned in a book I have from Organic Gardening magazine. They indicate using it for a Powdery Mildew Solution and Soapy Indoor Plant Spray. They also suggest this for controlling mealybugs, whiteflies, red spider mites, aphids, fungus gnats & scale.

- 1/2 to 1 cup rubbing alcohol
- 1 quart water
- pump spray bottle

1) Mix ingredients in a pump spray bottle.
2) Test spray on a leaf to check for burning.
3) Wait 1 day & check for damage before treating the entire plant.
4) Treat at 3-day intervals to 10 days or as needed. Don't use this in the heat of the day.

Do not use on African Violets.

If I have a problem with a lot of aphids, too many for squishing, I always use rubbing alcohol. Works great.

You guys really have to try the bacillus drops. I use Microbe Lift:
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=12263
Two drops in a spray bottle works fast (in one or two days) and will wipe them out for 6 months to a year. It's a safe biological control and organic compatible. It's less toxic to us than even alchohol or dish soap.
It's a miracle cure that works fast and good and complete. Try it! :^)