One effective and all natural way to combat whitefly greenhouse pests is to apply insecticidal soap . … Try making your own insecticidal soap with a recipe of one gallon water, 2 t baking soda, 2 t dish detergent, and 2 t white vinegar.
Just something I found online when looking for natural remedies.
I remember 20 or so years ago, I had a friend on Oahu, that had a nice little open sided greenhouse in his backyard. He had some big sativa crosses that everyone loved.
Problem was, his next door neighbor had a weed infested old flower bed that was infested with thrips…
I remember spending hours with a paint brush, knocking eggs off the underside of fan leaves, applying different types of mixtures-
In the end, he had great pot, and only a few people knew, that the buds were slathered in thrip shit…
I was cutting edge back then, and owned a lighted hand held microscope from radio shack
Azadirachtin drench your media. Its neem oil on crack…
Kills everything. Maybe two applications a week. Flush well after each use. Probably wouldnt use it after 3-4wks in flower tho. It sorts thrips, whiteflies and most nasties within 24h
Use with caution tho its nasty stuff. But ive been told it is safe to use in cannabis up to a certain stage in flower
I have never had whiteflies infest my cannabis plants. Whiteflies have destroyed many poinciana and tithonia plants of mine. The plants slowly decline as the whiteflies sucjk the sap out.
Now I have never engaged in any battle against these nasties, because they were ruining some of my ornamental plants only, my motivation to try to eradicate them was nil.
Whiteflies are almost undetectable with the naked eye. They are tough to eliminate if you have them. With the description @Calyxander provided, you can see that you need to continue treating until all eggs have hatched. At least two weeks spraying schedule to be safe.