I have a fungus gnat problem with my indoor herb plants and would like to apply Bacillus thuringiensis. Yesterday I bought six Mosquito Dunks and last night I cut off about 1/3 of one and put it into my 2-gallon watering can to soak overnight as I've read that's good practice.
Yet my plants don't really need watering right now, and I know that over-watering provides a perfect environment for fungus gnats!
So...should I water anyway, with the understanding that this particular watering with Bt soaked in will be helpful against the gnats? Or should I wait until the plants really need water? Though I'm hesitant to wait because I've been seeing the gnats for two weeks already (it took a while for what was happening to sink in!) and I know infestations can get really bad quickly.
As they state, dry is better to eliminate the gnats so I'd let your herb plants dry out rather than water. Save the Bt water till you need to water them.
I introduced the fungus gnats by an organic fertilizer for fruit trees and the little buggers drove me nuts. I used yellow sticky traps and allowed the soil to dry out. When I'd water again, they would reappear (probably a new batch). In this warmer climate I'd also move the affected plants out when the weather warmed.
Wishing you luck. What types of herbs are your growing this winter?
We had that problem with a plant at work and I just sprayed it with house and garden insect spray, then put 1/2 to an inch of aquarium gravel over the soil, that way the water can go in but the top stays dry, the gnats like the moist soil to lay their eggs in.