Dan, a big infestation of whiteflies can weaken a plant severely, causing decline, reduced production, and even death. Infested plants may end up with diseases, as well.

Since they are sucking insects, the damage can go unnoticed until it's almost too late. In my experience, they are difficult to control once they get the upper hand.

Parasitic wasps are great for controlling whileflies. Grow a lot of nectar rich flowers, especially those umbrella-shaped, for the beneficial insects all throughout the season and you will never have to worry about the pests in your garden, whiteflies included.

OK, so we're talking Neem, maybe? Though the other day I sprayed some dilute dishwashing detergent on the bed, and the numbers of whiteflies seems now to have dropped dramatically.

As to parasitic wasps, we have loads of paper wasps, which I keep around just for their insecticidal activity. Their nests are tens of feet away from the bed. Maybe not close enough.

Dan, parasitic wasps are extremely tiny insects almost resembling fungus gnats. I'm not going to explain their life cycle to you, but you should research it. Your paper wasps have zero interest in the whiteflies whatsoever.

What do you mean by spraying the bed? Do you understand that any contact spray you use must be sprayed directly on the pest? For whiteflies, a spray must be directed to the underside of the foliage, where the adults and disk shaped nymphs live.

The whiteflies I saw were on both sides of the leaves. When I sprayed, I saturated the top leaf surfaces. If a whitefly was on the top surface or landed there soon afterwards, it got drenched.

Paper wasps are classified as parasitic wasps. They happen to be predatory, which many are not. Not sure if they go after whiteflies, but they go after a lot of harmful insects. Certainly caterpillars. Encarsia are tiny parasitic wasps that do go after whiteflies almost exclusively. I'll farm cukes, but not encarsia.

Thankfully I have a garden and can grow my own!

I have an awful lot of whiteflies too and I have been trying to hose them off. I don’t think it’s helping much. I just bought a 3 in one organic spray and tried it for the first time Sunday night. They are gross flying out at you when you move the plants. I hope this stuff works. My cucumber plants did so much better than the tomatoes this year. Too many 90 degree days in Chicago for them to set.

daninthedirt: did you mean to imply that spraying the top of the leaves reduced the number of whiteflies under the leaves too?

Once or more, I would not eat cucumbers sprayed with dish washing detergent.

You eat off of plates sprayed with dishwashing detegent. I do, however, not advise consumption of dishwashing detergent straight outta the bottle!

I was just going to post something similar -- I've been infested with them. Weren't too bad earlier in the season on the cukes, but come about August it got insane! Finally had to take out the cukes mid-August, they got the life sucked out of them, they ended up all over the green beans and limas, moved onto the tomatoes, then migrated to the raspberries; it got so bad they were swarming in the air right by the gate, not even in the plants. Where they all came from and why it was so bad this year I don't know -- I don't recall noticing whiteflies at all last year. I give up -- it's time to start winding down out there anyway...

As I said, I sprayed the bed with the detergent mix. Heavily, so that the tops of the leaves were all wet with it. I have to assume that the whiteflies don't stay in one place, but move around in the foliage, so maybe when they land topside, they get soaped. In principle, you could soak the tops of the leaves, and then just brush the foliage gently with a rake. The whiteflies underneath will come pouring out, and lots will land on the leaf tops.

I'm a bit stunned at how successful this was, and I'm not entirely comfortable with the idea that the detergent dd the trick.