Fungus Gnats?

Difficulties related specifically to Semi-Hydroponic culture

Fungus Gnats?

Postby crjsci1 » Sat Jan 01, 2011 12:11 pm

Hi,

I primarily grow my orchids in semi-hydro in Wardian cases (Orchidariums). Because of the constantly wet environment, I have difficulty getting rid of fungus gnats.

The yellow sticky cards are great for getting rid of the adults, but I need to eliminate the larvae too.

Doing some research, it looks like one reasonable solution is to introduce Bacillus thuringiensis subspecies Israelensis (BTI) into the "soil".

Gnatrol seems to be the product that large-scale greenhouses use.

The folks at rePotme suggest that using a floating BTI laced mosquito dunk in your watering container will condition the water with BTI and can be used as a soil drench to get rid of fungus gnat larvae.

Has anyone tried BTI in their Semi-Hydro systems?

Are there other successful solutions for eliminating fungus gnats in semi-hydro?

Thanks!

Chris
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Postby raybark » Sun Jan 02, 2011 1:35 pm

The fact that you have fungus gnats in a semi-hydro pot indicates that you did not thoroughly clean the organic materials from the roots upon repotting. The ceramic medium will not support them.

BT is certainly a decent way to get rid of the larvae, but a watering with most broad-spectrum insecticides will do the trick, as well.
Ray Barkalow
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Fungas Gnats Continued

Postby crjsci1 » Sun Jan 02, 2011 3:12 pm

Hi Ray,

Thank you for your reply.

I should have noted that while I moved most of my plants to semi-hydro, I still have some orchids in bark or sphagnum moss, as well as several orchids on cork or fern mounts.

It is certainly possible that I did not thoroughly clean some of the organic materials from the roots when moving to semi-hydro as well.

Can you please recommend a good broad-spectrum insecticide that will work?

I note that while I have used a Physan solution to spray on some of the leaves, I have not treated any of my semi-hydro pots with insecticide before, so would like to learn what insecticides are good both for preventative care and maintenance.

I have just ordered some more Prime Agra so I can move more of my orchids over to semi-hydro.

Thanks,

Chris
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Postby raybark » Sun Jan 02, 2011 4:15 pm

I never use insecticides in a preventive mode, only remedial.

There is nothing different about using them with plants in semi-hydroponics than in "standard" culture, other than it's easier to flood the pot and medium for insects inhabiting the root zone.

Orthene (acephate) seems to work on fungus gnat larvae.
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Fungas Gnats Continued

Postby crjsci1 » Sun Jan 02, 2011 4:22 pm

Thanks Ray, I'll try both the BTI and Orthene solutions (in different Orchidariums) and report back.

Cheers,

Chris
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