To Sterilize?

writer333(Zone 4)April 27, 2014

I recently acquired an olive tree from a nursery and replanted it soon after arriving back home. After a few weeks, I noticed what I believe to be a fungus gnat flying around the pot area. I applied a systemic pesticide to take care of the problem, but as you can imagine, I would like to avoid using that method in the future so that I can enjoy eating my olives safely.

And so I have considered sterilizing any soil I use in replanting the tree in the future. I have read many articles on doing so, but the only problem is that most have stated that sterilizing soil will also kill any beneficial organisms along with the injurious ones. My question is: will this apply to my tree as well? I was thinking that there are still probably beneficial lifeforms left in the actual root ball of the tree, but I am not completely sure.

Any advice is appreciated, and thank you for your time.

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Understanding something about Fungus Gnats can help keep them under control. The link below can provide that information.
A systemic poison is not a Fungus Gnat control.

Here is a link that might be useful: About Fungus Gnats

    Bookmark   April 27, 2014 at 6:47AM
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writer333(Zone 4)

Thank you for the reply. I have read that using a systemic pesticide can kill off the larvae of this pest. My main concern is that if I sterilize my soil in the future, that I will still have beneficial organisms in the medium.

Here is a link that might be useful: Fungus Gnats as Houseplant and Indoor Pests

    Bookmark   April 27, 2014 at 6:56AM
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Look around for something called "mosquito dunks" - they contain a bacteria that enters the intestines of mosquito larvae and causes crystals to form, killing them. This works on fungus gnat larvae.

It also comes in granules. I just sprinkle a teaspoon of granules on the soil surface of potted plants, as well as when I'm potting up seedlings, and that takes care of it.

Here is a link that might be useful: mosquito dunk granules

    Bookmark   April 27, 2014 at 11:25AM
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darth_weeder(z7 NY)

Are you growing the olive tree in a pot or in the ground?

    Bookmark   April 27, 2014 at 12:32PM
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Are you really in zone 4? If so, you must be growing this tree in a container. Fungus gnats in potted plants are an indication of overwatering or excessively moisture retentive potting soil. The easiest thing you can do is repot with fresh, dry potting soil and don't water as frequently as you have been. Olives are Mediterranean plants and are accustomed to dry conditions - they don't need much water.

Another way of dealing with fungus gnats is to spread a layer of coarse sand over the top of the pot. The adults are disinclined to lay their eggs on the sand and the population will die out in about a week to 10 days.

Good luck harvesting olives from this plant....they are not known to produce fruit as a houseplant.

    Bookmark   April 27, 2014 at 5:25PM
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writer333(Zone 4)

Yeah, I'm in Zone 4, South Dakota, to be exact. And I'm growing the tree in a pot indoors. I replanted the tree in a mixture that is well-draining, but it is possible that the root ball has the fungus gnat larvae in it, as the soil there is much more dense and able to hold water. I've tried watering less frequently in the past, but the tree would start shedding leaves, and so I upped the watering frequency and now it is keeping all of its leaves.

    Bookmark   April 27, 2014 at 9:14PM
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Soil does have beneficial microorganisms in it, in fact plants would not thrive very well without them since they do quite a bit of the work of circulating nutrients. I think trying to sterilize the potting medium for a plant is not necessary and probably a futile undertaking.

If I saw a fungus gnat I would ignore it. If I saw three or ten I might look into controlling them as suggested.

    Bookmark   April 28, 2014 at 4:15PM
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