Can Mosquito Dunks Kill Fungus Gnats and Fruit Flies?

This is a question I am hoping to answer via some experimentation in the near future.

Some may recall that I tested out the nematode, Steinernema feltiae, as a fungus gnat killer last year and found that it was reasonably effective. The problem was that it was a fairly expensive solution, and generally would require ongoing applications in order to keep the gnats at bay over the long haul. Incidentally, I also tested Steinernema against fruit fly larvae, but I discovered one of the other limitations of this biocontrol organism – that being heat intolerance (at least I am pretty sure that’s what the main issue was).

And if those limitations aren’t enough – perhaps I should remind you of the fact that Red Worms have been shown to kill these nematodes as well!

I have read that some people have used ‘mosquito dunks’ successfully to control fungus gnats, so I’ve decided to try them out myself. The advantage of this approach (assuming it works) is that the dunks are a lot less expensive (especially when you consider how long a package will last in comparison to nematodes), and just generally less of a hassle to deal with.

I’m thinking that if I simply immerse a small chunk o’ dunk in a container of water (a full dunk is apparently enough to treat 100 sq ft of water area, so using a full one might be a bit of overkill – haha), then use that water to moisten an infested habitat, it should (hopefully) work.

I’m definitely not as optimistic about the effectiveness against fruit fly larvae, but you never know. Fruit flies are in the same Order (Diptera) as gnats and mosquitoes, but I don’t know if there is enough similarity. The particular strain of bacteria, Bacillus thuringiensis israelensis (say that three times fast!) is specific to dipteran pests, while other strains are used against beetle larvae, caterpillars etc – so that gives me some hope.

The key will me to make sure there is enough of this bacteria in the test systems that it ends up being ingested.

Anyway – I will be getting some experiments up and running in the next week or so, and will write a post once I am ready to roll.

Written by Bentley on August 14th, 2009 with 8 comments.
Read more articles on Home Vermicomposting and Worm Bin Creatures.

Vermicompost Vitality

Here’s a question from Corey:

Thanks in advance for all your work and info! It’s truly
appriciated. I have what may seem to be a silly question, but here it
goes : Does harvested vermicompost lose its virality/vitality over
time during storage? My concern is that harvested casings during the
off growing season would sit unused for a few cold months before being
incorporated into the garden-may lose its potency. Just a thought -
but it never hurts to ask -

thank you!

Corey in PA

Hi Corey – that is actually an excellent question (which is why I decided to post it on the blog). The short answer is definitely “yes” – but there are lots of factors involved (and potential scenarios) here so I certainly won’t leave it at that!

Using high quality vermicompost soon after it is harvested will almost certainly provide you with more benefits than if you use the material after it’s been sitting for 5 years. Unlike a fine wine, vermicompost doesn’t really improve with age (haha). A short ’sitting’ period can definitely be advantageous in some situations however. You’ll notice I mentioned “high quality vermicompost” – well the stuff that often comes out of the bottom of a ‘Rubbermaid’ tub type of worm bin generally doesn’t fall into this category, in my humble opinion. This is especially true if there are no drainage holes.

This material will very often be overly wet, with anaerobic zones – and may in fact not even be finished vermicompost. Material like this should allowed to sit someplace where excess moisture can drain away and there is plenty of air flow to aid with the drying process and provide plenty of oxygen to allow the aerobic microbes to finish the job.

In the case of the really good quality stuff – material that is harvested from some type of flow-through system for example – the storage stage isn’t really needed, and it will likely be at its peak for beneficial microbial activity. If it is left to sit, microbes will gradually start to die off and/or become inactive since there won’t be all that much ‘food’ value left – it will be rich in humus and thus highly stabilized.

Now don’t get me wrong here – if we take the scenario you mentioned, in all honesty I don’t think you will lose a signficant amount of the potency during the winter months of storage – especially not if you are able to store the material in a cool, relatively dry (don’t let it completely dry out though) spot. Perhaps in your basement somewhere? The cool temperatures (and low moisture content) will slow down the microbial activity, thus also slowing down the ‘aging’ of the vermicompost.

You might also think about doing a gradual freezing of the material. While I probably wouldn’t recommend simply throwing a bag of fresh vermicompost straight into a chest freezer, if you start storing the material in an outdoor shed in the fall, my hunch is that you’ll get a higher percentage of microbes becoming inactive (forming resistant cysts), rather than being quickly killed.

Perhaps you have a spare fridge somewhere? I would think that this could be a good way keep your material fairly fresh as well.

By the way – some other ways you can really speed of the decline of your vermicompost include letting it sit out in the rain and/or hot summer sun. Precipitation is basically just going to wash away a lot of the ‘good stuff’, while the hot sun will likely just end up sterilizing the material.

Anyway – I hope this helps, Corey! Thanks for the great question.

Written by Bentley on August 14th, 2009 with 6 comments.
Read more articles on Reader Questions.