As we all know, Bacillus thuringiensis serotype israelensis (BTi) is effective natural pesticide to control Fungus Gnats. So how do we measure BTi? Which product is the best "deal" for buying BTi?
Well, that question requires a little back of the envelope math before one can actually compare different BTi products. You see, BTi is measured in International Toxic Units (ITU) at various concentrations ranging between 100 to 7,000 ITU/mg. The "Active Ingredient Percentage" on the label is just part of the story...gotta include the amount of ITU/mg.
An 8% "active ingredient" product formulated with 1200 ITU/mg has 96 ITU (1200 x 0.08) for each milligram of product.
A 3% "active ingredient" product formulated with 7000 ITU/mg has 210 ITU (7000 x 0.03) for each milligram of product.
Hmmm, that means the 3% products has nearly twice the amount of ITU than the 8% product. WTF?
Also, application methods are different. Some products are RTU (ready to use) for both soil and water applications, others like Vectobac require the preparation of fermentation slurry to activate the BTi, and some are only water soluble (not to be mixed directly with the grow medium).
Since not all BTi products are "equal", I have prepared a comparison of the "usual suspects" and correlated everything to cents per million ITU.
Gnatrol is the most affordable, but can only be used in a liquid suspension form--you can not add the powder directly to the grow medium.
Bits is the 2nd most affordable and can be added to both water and the directly to the potting soil. When added to the water, BTi is instantly activated...but when mixed with potting soil, BTi is gradually activated (time release of sorts) for about 21 days.
Bits are basically corn cob bits sprayed with BTi.
Dunks are slow acting (gradual release as the "donut" dissolves) and can be added to the potting soil directly--but must be crumbled to a powder like consistency (PIA).
Dunks are pressed donuts made of gypsum and cork bits sprayed with BTi.
I have no experience with Vectobac products but a special fermentation slurry must be prepared before the BTi is activated (an additional step that most BTi products do not require).
Microbelift BMC is already in liquid form and like Gnatrol, it must be diluted in water before use...and from my analysis, is not a bargain.
I previously used both Gnatrol and Dunks, but for the past few years I exclusively use Bits for my source of BTi ($120 for 5 gallon bucket). I mix Bits directly to my water (30 ml/20 gallon rez), mix Bits directly in the potting soil (5 ml/5 gallon container) and mix Bits with my top dressing fertility (7.5 ml/5 gallon container).
One product for all. Admittedly, I could use Dunks form my water rez, but since that rez is used and refilled daily, I prefer the faster acting Bits over the slow release Dunks.
So there you have it. If there are other BTi products you want included in my analysis, please let me know and I will be more than happy to add them.