Fungus gnats!? Grow Room Threat: Orange! Small, pesty flies, two or three
millimeters long, like many mosquitoes, but they don't bite, or sting. No, instead
they love to crawl and creep around on plants and growing media! They fly around
stupidly, getting in your face, buzzing from place to place, slowly and seemingly
without purpose, but somehow very irritating at the same time-- kind of like
my father-in-law on Facebook! Some growers confuse them with winged root aphids,
which are better fliers, with a rounder broader body, and are more
attracted to your grow lights. Sure, the adult gnats, themselves, don't do any
damage, but they love to fly into my eyes, and up my freaking nose, and seem
to have a sixth sense of when I have both my hands full and I can't swat at
them, but okay. It's their larvae-- hatched from tiny eggs laid by the female adults
in moist growing media-- that cause all the issues, especially to young plants.
The fungus gnat larvae primarily feed on organic material, algae, and soil fungus,
but in increasing numbers, that necessitates a broader diet, including
roots, and plant stem tissue. Yes, they nibble on your plants' roots, people! This
in turn creates wounds, which open up the gateway to secondary infections from the
likes of Pythium, Phytophthora, and Fusarium. Seedlings and younger plants
can die! Older plants could stop growing! Leaves will discolor and wilt, and nutrient and
water uptake will slow! It's-- enough talking already.
Let's go neutralize some gnats. As with all pests, you must first understand
their lifecycle, and disrupt it, preferably, at multiple stages at once.
Ignored fungus gnats will breed uncontrollably, and a few weeks after
spotting a handful of gnats, you'll have a major infestation on your hands. Fungus
gnats can hitch a ride into your grow room on your clothes, or cuttings
accepted from friends, through gaps between doors and walls, in soil, compost,
and soilless potting mixes. Once introduced, they seek out moisture and
humidity. Top feeding your plants too often creates ideal breeding conditions,
that is, moist surface growing media. Consider irrigating your pots from below,
and allowing your plants to wick up moisture instead. At the very least, ease
off with irrigations, and let your growing media dry out more between
waterings. Now, adult fungus gnats enjoy a brief moment of sexy time together and
then the females lay their eggs in your growing media-- sometimes also in the
algae that forms at the top of stonewool blocks.
Try using block covers, or fashion some yourself with little squares of correx, or
plastic sheeting to stop the algae from forming in the first place, and to form a
physical barrier against the gnats. Okay, now that we know our enemy better,
how do we kill them? I recommend a two-pronged approach, my friends. Target
adults with foliar sprays and traps, and larvae with nematodes, mites, or
biological larvicides. Now, you should always have some yellow sticky traps in
your store cupboard-- even better: already in your garden. Sticky yellow traps are a
handy monitor for pests, not just a reactive measure. Peel the protective
wrapper from both sides, and lay them on the tops of your pots, like this, rather
than hanging in the air, so they catch emerging adults. Next, call your local
grow store, and ask them if they have any predatory insects in stock. Do this
right now because chances are they may have to order them which can take a few
days. For the adults, try something like Azamax, a botanical insecticide. miticide,
and nematicide. Use a foliar spray for a few days before sending in any
beneficial insects. Make up a medium strength solution: one fluid ounce per
gallon, and foliar apply immediately. Work fast, wear a respirator mask, and get the
hell out of there. Just like the zombie apocalypse, my friends. As for killing the
babies, if you have cuttings or seedlings in blocks, you can dip them
into a bacterial larvacide containing Bacillus thuringiensis Israelensis, or
BTI, such as Gnatrol WDG or Mosquito Dunks. Woo! Sorry, got a little carried
away. Remember, if using multiple combat methods, it's important to know that
they're fully compatible with one another, as some pesticide products will
kill your predators. Also, ask your grow store for advice on specific product
combinations. Parasitizing nematodes are incredibly effective against fungus gnat
larvae, and can decimate fungus gnat numbers in days, while causing no harm
whatsoever to your plants. The nematode species of choice for this application
is: Steinernema feltiae. You can buy them in little packets. It
looks like dust, but lurking within are millions of tiny little beneficial
nematodes. Note the use-by date on the packet. The nematode enters the body
openings in many types of soil larvae and uses them to breed-- killing the
larvae in the process. Excellent! Fill a watering can with dechlorinated
water, and then add the nematodes, and stir; apply carefully and evenly to the
surface of your growing media. I redirect the drain pipe of my ebb and flow table to
catch the runoff so I can reapply to other plants. They won't survive long sat
in water so use it up right away. Hypoaspis miles:
a tiny, predatory mite, invisible to the naked eye, has recently been reclassified
with an even catchier name-- Stratiolaelaps scimitus. Many growers deploy
these mites is a preventative measure as they can last up to 70 days without food,
so why not just let them hang out, just in case. Usually they come prepackaged in
sachets or tubes of peat and vermiculite. A 34 oz container of Stratiolaelaps scimitus
retails for around 40 dollars, and can treat between 100 and 200 3 gallon
pots, so it's not going to break the bank. Sprinkle it onto the surface of your
growing media, and you're done. If you can't get ahold of predatory mites, then
try a top dressing with diatomaceous earth, Growstone Gnat Nix or Gnat Block by
Flying Skull. I use DiaHydro, which is fairly chunky. Try to get the most
powdery stuff at the bottom of the bag. Diatomaceous earth is fine for us to
handle, but to a newly-born gnat it's like crawling over a razor wire. It's only
really effective when dry so try not to get it wet.
Once again, flooding from the bottom is the preferred method of feeding. Some
growers use neem cake in their soil mix, or neem seed meal as both a soil enricher,
and a preventive measure against fungus gnats. If you're growing in NFT
grow tanks, then be aware that capillary matting is also a favorite for fungus
gnats, so be sure to secure the tank covers well to avoid gaps. Finally, don't
forget to secure your air inputs with intake filters or bug screens, and always
keep your grow room clean and tidy. If you've been gardening outdoors, take a
shower, and change your clothes, and footwear before entering your indoor
garden. Thanks for watching, and don't forget: if you have methods of fungus
gnat control, or techniques for complete annihilation that I've failed to mention,
then please don't forget to share them with us in the comments below.
Sometimes battles with fungus gnats can last for months, even years, but don't
lose heart, just stay on top of it. Remember to always read the label, and
take proper precautions when using any pesticide products, especially indoors, my
friends. Hit that subscribe button, you know you want to, and it's free and easy,
just like a pair of frisky fungus gnats having a last Tango in midair before
meeting their inevitable demise. Life is so short, amigos, and on that note, I'll
bid you farewell until next time. Adios!