Fungus gnats? Insecticides in heat?


(Deborah Ballanti) #1

Hi all.

I have recently noticed many small black flies/gnats congregating in the soil of a number of my bonsai…from maples to spruce.

I live in Sacramento, have been watering a lot due to high temperatures and recently started using organic fertilizers which I simply spread on top of the soil. After reading online, I am guessing these are fungus gnats attracted to the moisture and fertilizer. I could be mistaken and would be interested in other thoughts.

I will remove the fertilizer today and try watering less.

The questions: Can I use an insecticide? If so, recommendations on which one? Can it be applied in this heat? (90’s - low 100’s).

Thanks for any input.


(Frank Corrigan) #2

Removing the organic and allowing the surface to dry out between watering should do the trick. I would try that first before going for any insecticides.


(Deborah Ballanti) #3

Thanks, Frank. Will do. Appreciate the input.


(Mike ) #4

Might try Insecticidal soap. If have used it in the past. Mild on the tree in the head too.

As mentioned, etting the tree safely dry out is best preventative


#5

Fungus gnats are a real nuisance during the “rainy season” here in coastal SoCal and love to get inside the house. I have taken to using mosquito dunks, which have the bacteria bacillus thuringiensis (Bt). I get the kind that are granular in a dissolvable packet and break them open to sprinkle in the garden, flower beds, etc. I also sprinkle them in my nursery cans that have a higher organic substrate portion. At the low rate that I sprinkled them out, it doesn’t seem like it would do much, but there has been a noticeable difference for several years. I also use a garden store boxed organic fertilizer which lists Bt in the ingredients.


(Darth Masiah) #6

you could use a top dressing of growstones gnat knix if you dont want to spray anything. the growstones have sharp edges that kill the gnats. probably the simplest approach ever.


(Deborah Ballanti) #7

Thanks to all for the suggestions. I got rid of the organic fertilizer for the time being and let the soil dry out a bit…seems like they are gone for now. I will definitely save your suggestions.