Fungus Gnat?

[maveriiick]

Hello, I just wanted to get verification on this one. I've had gnats before but they were much larger than the tiny flies that are flying around right now. They are about 3-4 mm in length and fly very eradically but also very swiftly and are hard to kill. My previous encounter with the larger gnats was that they were cumbersome flyers and very easy to kill. Anyways, I haven't seen any kind of worms/larvae on the top soil but a few leaves on my grewia have been discoloured as of late. Is this a fungus Gnat or something else?









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[rainbowgardener]

Sounds like fungus gnats to me, both the size ("Adult fungus gnats are about 1/8 to 1/10 inch (2.5 mm) long" http://ohioline.osu.edu/hyg-fact/2000/2114.html ) and flight description. Maybe what you had before was some other kind of gnat or fruit fly. When I have had fungus gnats before, they tend to crawl around on the surface of the soil alot, but when disturbed they fly and fly fast, hard to catch. The larvae would be farther down in the soil (eating the roots of your plants!), not visible unless you dig.

[applestar]

I'm not seeing the classic tapered, pointy abdomen of fungus gnats in you photos. Also if you're implying that the leaf damage is due to these "flies," I don't think fungus gnats would be the culprit since, as rainbowgardener mentioned, they're mostly pests in the larval stage in the soil and tend to affect young seedlings or newly rooted cuttings -- not so much mature plants.

I posted most of what I know about fungus gnats in this thread There's a photo of a fungus gnat a few posts down.

I won't venture a guess as to what this bug is, though it strikes me as similar to a couple of bugs I've seen around here -- One swarmed all over my bush beans, got stuck on the foliage and stems and died without causing any apparent damage to the beans. Another look-alike is trichogramma wasp, which is a beneficial insect.

[maveriiick]

Just following up. I tried an apparent fungus gnat trap, which is cider vinegar in a glass with one way entry (inverted paper with edge toward the vinegar) and no luck. I still see these very small flies and the problem continues with the Grewia with yellowing of the leaves and leaf drop which takes about 3-10 leaves a day, which is not normal. I've even allowed the soil of the grewia to dry out more than normal. The plant appears be fairly healthy otherwise, but I know something is going on (but still don't know what?) I haven't seen any soil larvae and I've looked long and hard and I shoot the little fliers with alcohol spray to knock them down and kill them, but I am sill looking for clarity and significance of their presence?

[The Helpful Gardener]

If these are recurrent around the same plants, then it is likely the larvae reside in one of them. A dose of Steinernema feltiae should take care of the larval stage, fungus gnat or not. Nematodes are not always bad guys!

HG
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Scott Reil
The Helpful Gardener