I might agree about the Imidicloprid comments in principle, but not in practicality. First, a soil drench on a couple of trees isn't like wholesale spraying of the landscape. Second, while I'm certain that trees in bloom attract bees, most of my trees bloom in the spring when soils are cold/cool and gnat activity is nil. Also, I've never seen a bee hovering around my fig trees - closed inflorescence and all that. Bees, wasps, other beneficials and their larvae can all end up as secondary casualties to other methods (BTI, DE, other insecticides), so there is often collateral casualty associated with even the best IPM plan once you reach the treatment stage.

I offered 4-5 suggestions, all of which would be variably effective at controlling gnats, applied individually or in combination. I think that of all the suggestions, the imidicloprid would be fastest, most effective, and the longest lasting. If there are politics associated with its use, I'll let others wrestle with that issue. That's probably for the OP to decide - I wouldn't presume to substitute my value set or a personal ideology for someone else's.

I never have infestations of the beasts. In my mind, the best cure is prevention, and I've found that well-aerated soils and discipline in watering habits to be excellent prevention, and that's what I suggest, not only because of the gnats, but because of other far reaching benefits much more important than gnat control.

I live in a nice neighborhood on a good size cul de sac with about (I'm counting) 18 homes on it. Of the 18 homes, at least 2/3 - 3/4 have a lawn service. Grubs are a major problem in our area, so I'm sure all or nearly all and probably some of the others w/o lawn service are using Merit or some other form of imidicloprid on their lawns to control the grubs. I think that if we want to look for offenders, we should look first to agribiz and other SIGNIFICANT users of imidicloprid, not to the poor sole who has a few trees in pots to dose via a soil drench.

That's just my take. Like I said, I agree in principle but not in practicality. I have some very surprisingly valuable bonsai trees. My first line of defense against scale is imidicloprid. I use it responsibly, and can't make the connection between how I use it and the destruction of our food supply.

BTW - the effectiveness of DE is significantly reduced when it's wet or damp due to the clumping effect and the fact that water acts as a lubricant and inhibits DE's ability to absorb the insect's waxy cuticle - a mechanism quite different from the commonly held belief that it's the abrasive/cutting effect that causes desiccation.

Take care.

Al

>>> enjoying a pint of Guinness, gnat fell into my glass...

One of them (flutter), managed to sneak upstairs into my bedroom
and then get close enough to get inhaled through my
nose (think-wing-flutterrr!).

I think there is probably 2 ways to read the blip that Gina provided. On one hand, if you are already predisposed to believe that imidicloprid is an awful chemical, it can be read to support that position. If you're critical about what it actually says ...... well, let's read it together with emphasis added.

Farmers worldwide have been using one popular neonicotinoid, imidacloprid, for about a decade to keep harmful insects off their cotton, corn, grains, potatoes, rice, vegetables and other crops. Like other neonicotinoids it targets the nervous system of insects, resulting in paralysis and death. Because honeybees (Apis mellifera) are insects, too, biologists have long suspected [not very conclusive - the author isn't sure] neonicotinoids as a possible [this is very vague - it's possible that it could also be any one of several thousand other causes] force in colony collapse disorder. [The first thing I thought of was 'intentionally scary with no real substance, and the entire article is laced with 'mights & maybes']

 
Researchers have now found that repeated low-dose exposures are perfectly capable of gradually killing of whole hives of bees [sic]. [I'm having trouble imagining an insecticide that doesn't/wouldn't act in such a manner, along with thousands of other common substances that if 'fed' to bees in repeated low doses wouldn't kill them] In fact, 94 percent of hives whose bees had been fed the pesticide died off entirely within less than six months, according to a new paper that will be in the June issue of Bulletin of Insectology.

I really have no opinion one way or another about whether or not anyone should or shouldn't use imidicloprid. I don't think the manner in which I use it is worth my fretting over. I do think that if I was invested in determining if there was a moral obligation for me NOT to use it, I'd be looking for something scientific. I'm not even saying that something scientific and definitive doesn't exist - there may well be studies that conclusively show that imidicloprid use is indeed a significant cause of diminished bee populations. What I'm saying is that I'd quickly bypass the article in Scientific American because it doesn't show/conclude anything and because of the bias that's so obvious in the manner in which it was written.

Finally, the Bayer toxicologist said the concentrations were unrealistic. The reply to this assertion was, “Our experiment included pesticide amounts below what is normally present in the environment.” As I read this, the question I wanted answered is, if doses lower than what is normally present in the environment are killing bees, why are there bees? Shouldn't they ALL be dead because the amount of imidicloprid normally found in the environment is greater than a lethal dose?  

Al  

Dave - You might be interested in knowing that if you use one of the flea control medications that you apply on the back of your pet's neck, you're applying imidicloprid. It's also used remedially and prophylactically for ear mites, heart worm, and a variety of intestinal parasites (worms).

Al 

I have had fairly good success by keeping the surface of the soil light and fluffy (the top 1/2 to 1 inch) and by bottom watering only.  The idea behind having the surface fluffy is that it will dry very quickly.  If the soil surface is dry there is no (or very little) fungus growing on damp, decaying organic surface material, which means the gnats are not attracted.  If the surface is packed down, it may wick water from below even if you bottom water, and it will be slow to dry.  Gnats burrow a bit into the soil so if the fluffy surface is too thin, they may still be attracted to the damp and decay that is just below.

A few years ago I had an infestation near the grow lights in my cellar, I think from a "sterile" planting mix that I bought.  I went around to every pot/planter and scratched up the top 1/2 inch so that it was fluffy and in a few weeks the gnat population went down to maybe one every few weeks.  Unfortunately, every spring I have many dozens of seeds starting (tomatoes, peppers, etc) in very small containers and it is impractical to keep the top of the soil fluffy and dry.  So for a month each spring there is usually an infestation.  But once those go outside, the dozen pots that remain inside are maintained fluffy and dry on the surface and the gnat population drops back to zilch in a week or two.

I suppose instead of fluffing the top 1/2 inch, you can replace it with something which will drain and dry quickly.  I've heard a suggestion that putting a half inch of vermiculite on the surface of each pot/planter works.  My guess is that it works because it drains and dries quickly, again providing a surface with no decay and fungus to attract the gnats.