possible fungus gnats and treatment possibilities

Asked April 3, 2016, 8:24 PM EDT

After using a bag of cheap soil for seed starts, I think I have an infestation of gnats (or something). Very tiny winged creatures are in the air and scurrying around on the surface of the pots when I water or spritz. I have tried Neem oil and pyrethrin sprays without noticeable effect. Could I use BT Kurstaki with the same success as BT H14 (if I truly have fungus gnats)? Would baking any soil in a shallow layer before potting up have killed these buggers and, if so, at what temp and time?

Cass County Minnesota

1 Response

The pests you have described probably are fungus gnats.

According to authorities at the University of Minnesota, "the only effective product for treating fungus gnat larvae in the soil is a bacterial insecticide, Bacillus thuringiensis var. israelensis, (e.g. Knock-Out Gnats). Also known as B.t. H-14, this insecticide is specific to fly larvae."
http://www.extension.umn.edu/garden/insects/find/fungus-gnats/

This appears to be a reliable source of information about heat treatments to control fungus gnats in potting media:
https://greenmethods.com/greenhouse-bake-out-to-control-fungus-gnats/

This thorough discussion of the problem is also reliable and may be of interest:
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7448.html