FUNGUS GNATS (Bradysia coprophila)
Fungus Gnat larvae attack plant roots. They feed on the roots and weaken the plant. This not only weakens the plant directly, but can make it more vulnerable to diseases which Fungus Gnat larvae themselves can pass on.
NATURAL ENEMIES OF THE FUNGUS GNAT
Stratiolaelaps scimitus (Hypoaspis miles)
Since you’ve already been using Stratiolaelaps scimitus generously to prevent those pesky Spider Mites, Fungus Gnats may not be a problem. But, once again, it’s always better to keep an eye open and prevention, as the proverb goes, is better than cure.
If you’ve used Stratiolaelaps scimitus and you then still spot Fungus Gnat larvae in the soil, then get going with more Stratiolaelapsscimitus. Stratiolaelaps scimitus works best against Fungus Gnats before a proper population starts to thrive. Check your traps, and if there are fewer than 10 Fungus Gnats in the week, then you can consider the population low. If you catch the Fungus Gnats in their larval stage or in this early stage of low numbers, you should only have to apply Stratiolaelaps scimitus twice, once when you discover them and a second time two or three weeks later. This should cover your whole crop cycle.
In the soil or in whichever medium you’re using.
Rove beetles (Dalotia coriaria or Atheta coriaria)
Rove beetles are also good enemies of the Fungus Gnat. They’re maybe not quite as efficient as Stratiolaelaps scimitus, so it’s a good idea to use them both together.
Rove beetles don’t get to work as quickly as Stratiolaelaps scimitus, they take longer to establish. For that reason, they’re best included before your Fungus Gnats start appearing in the trap, or when you seen a single one. The good news is that Rove beetles have a long life cycle, compared to Stratiolaelaps scimitus, so you’ll only need to apply them once during your crop, but get in there early.
Nemasys is a clever product, or, rather, it contains clever predatory Beneficial Nematodes, which are powerful enemies of the Fungus Gnat. Nematodes are unsegmented microscopic worms, with rounded bodies coming to points at both ends. There are different types of nematode, but the Beneficial Nematodes of Nemasys are very useful to the indoor cannabis grower. These Beneficial Nematodes (Steinernema feltiae) will sit in the soil and kill Fungus Gnats and other nasties without damaging any other organisms. The Beneficial Nematodes enter the Fungus Gnats’ bodies and release bacteria leading to blood poisoning and summary death of the Fungus Gnats. The Nematodes then use the Fungus Gnats’ bodies as hosts in which to reproduce. The new nematodes head out and do the same to other Fungus Gnats. And so it goes.