Orchid Pest? - Orchid Board

chips · #1 04-25-2009, 07:18 PM

I am not sure if I am having a problem. I have these small insects(look like fruit flies) flying around my Phals. The Phals have no problems, they are in full bloom, no leaf or root damage. The little flies seem to be more interested in the potting soil than the plant. Can orchids attrack fruit flies or are they something else?

camille1585 · #2 04-25-2009, 07:24 PM

They probably aren't fruit flies, but fungus gnats instead since they stay near the plants. Do you see them resting on the surface of the medium? The flies themselves aren't the problem, it's the larvae. They munch on roots. I've never had them on orchids, but on other plants I've dealt with them with an insecticidal drench.

chips · #3 04-25-2009, 08:54 PM

What do I buy to get rid of them?

kiki-do · #4 04-25-2009, 09:23 PM

I get fungus gnats whenever I have orchids in bark that is getting old. I also have them because of my passion flower. I hang a fly strip somewhere above or around the plants the gnats are attracted to. Some places sell fly strips that are small and you stick it in the medium and the gnats get stuck on them. I see that alot at greenhouses. They don't harm anything, I don't think, but are a nuisance.

ChasWG · #5 04-25-2009, 09:28 PM

I have used various household soaps. The soap is not harmful to the plants, but it kills the gnats. Also, the soap acts as a water wetter, basically lowering the surface tension of the water and allowing the water to penatrate potting soil.

Now, I have never used this technique with orchids, so I can't say one way or the other.

axle · #6 04-25-2009, 10:57 PM

The larvae can supposedly be killed with Bacillus thuringiensis, that's not a brand name. Rather it's the name of a bacteria that feeds on larvae of mosquitoes and supposedly fungus gnat (larvae).
Big box stores usually carry products containing BT in the pools/fountains maintenance section.

The product I have comes in little <1/4" wafers. You can add a few to your potting mix or mix with water and let it brew for a day.

Still, I think the best solution for getting rid of gnats is to let your potting mix dry out completely between waterings.

I think it's a misconception that fungus gnat larvae feed on roots. I believe they feed on decomposing organic matter. If your roots start to rot then they're fair game I'm sure.

Now I'm not saying that you're mismanaging your plants, if you've got blooms and roots your doing great and probably better than me. But imagine if you could analyze every square micrometer of your potting mix there's probably plenty of habitable areas with proper wet/dry cycles for roots. But there's bound to be small areas that stay wet ridiculously longer than the rest of the mix.

chips · #7 04-25-2009, 11:05 PM

I don't think I am overwatering, at the moment my one Phal has 26 blooms on it and is in lovely condition. Could the problem be, I frequently mist the air roots, thus the top of the potting mix is wet for a period of time in the day?

camille1585 · #8 04-26-2009, 05:56 AM

Quote:

Originally Posted by axle

I think it's a misconception that fungus gnat larvae feed on roots. I believe they feed on decomposing organic matter. If your roots start to rot then they're fair game I'm sure.

They do feed on roots as well as decomposing organic matter. But I don't think it's much of a problem for phals, since they have such thick roots. The larvae are more of a problem for normal houseplants, particularily the younger plants, and the effects of their feeding are only seen after a long period of time or when there is a high number of larvae in the pot.

neb · #9 04-26-2009, 07:32 PM

Like ChasWG said a little soap can help get rid of them. I had a bad infestation that came with an Amaryllis all I did to get rid of the gnats was squirt some antibacterial dish detergent in the media of every plant, orchid or not, then wash all the suds out. The water running through was able to carry the suds allover the media and roots.

Judi · #10 04-27-2009, 10:43 PM

I was under the misconception that fungus gnats don't harm roots so I ignored the little buggers. After a while my chids just didn't grow well. After some internet research I found the larvae will feed root tips as well as decomposing medium

. I controlled my problem with "knock-Out Gnats" from Gardens Alive; it is the bacillus thuringiensis. I also use the yellow sticky tabs, try to dry out the pottng medium, and flush the pots with running water on a monthly basis (we don't have chlorine in our water). My orchids are growing better and are much happier now