If you remove the Gardenia, the whiteflies will have to find another home. I'd let nature handle it, something will probably show up and eat most of them.

Well, I gotta disagree with purple on part of her answer. Gardenias are so susceptible to whitefly infestations that mother nature cannot fix the problem once it gets out of control.

Is this population so bad that black sooty mold has started to cover the leaves?

A heavy (very heavy) infestation can cause such decline that the plant can die. Though whiteflies have plenty of natural enemies, they might not be much help. But, there are a few things you can do to control the pests without doing much damage to the beneficials.

First of all, the adults and the disc-like nymphs and pupae and the eggs are ALL located on the underside of the leaves. Any overspraying is virtually useless, except in getting the few adults that flit out. Nymhs feed heavily. Insecticidal soaps have no residual effect nor are they helpful in controlling the eggs and nymphs. They can, however, harm beneficials.

I've had very good results with horticultural oil sprays, applied several times over many weeks TO THE UNDERSIDE OF THE FOLIAGE. If you can't do that, just forget it. The oil smothers the eggs, nymphs, and pupae. If you use neem oil occasionally as one of the oils, you will also add the qualities of a growth regulator as well as oil...with very little damage to beneficials.

Since I cannot see how bad your problem is, I can't suggest that you need to go to plan "B" or even just yank the plant. They will find other plants to feed on, but not usually to the extent that they will on gardenias..

The only plant I use a commercial spray on is my gardenia for the whiteflies...Bayer Advanced Lawn and Garden Multi-Insect Killer. I don't see it listed on their page. It looks like the 2-In-1 Systemic Rose & Flower Care would work.

Here is a link that might be useful: 2-In-1 Systemic Rose & Flower Care

The only plant I use a commercial spray on is my gardenia for the whiteflies...Bayer Advanced Lawn and Garden Multi-Insect Killer. I don't see it listed on their page. It looks like the 2-In-1 Systemic Rose & Flower Care would work.

Here is a link that might be useful: 2-In-1 Systemic Rose & Flower Care

Thanks, Rhizo! The wisdom of someone with decades of experience cannot be denied. I wouldn't presume to know as much about pests or Gardenias.

As a general rule though, it seems that something would have to cause the 'denia (or any plant) to be unhealthy in general to be so vulnerable to a visit by pests, like not enough sun. I've seen various critters visit the 'denias in my yard and the abandoned yard next door but the plants never seem much bothered by it.

When it was really dry a couple summers ago, the big one in my yard got a lot of sticky black stuff on its' leaves and had whiteflies and aphids on it. I blasted it with the hose, trimmed a lot of material out of the middle, and moved the mulch/leaves away from the trunk a bit more, gave it a drink. It soon looked fine. The shrubs next door went through the same symptoms but of course nobody did anything to them. They also recovered well. This is one of those tough plants I see commonly thriving when abandoned in the unfortunately high percentage of abandoned properties around here.

I'm wondering if Namarie's shrub is new, or if the garden is generally new. OTOH, it could be quite old and have gotten more shaded by enlarging nearby trees. A pic of the area, or just knowing what is thriving nearby might help determine why this shrub's gotten unhealthy. Maybe just too much cold muck this spring?

Not that a treatment might not be necessary to save it at this point, I'm just left wondering about the bigger picture. Rhizo knows, but you should know I'm in the camp where I'd rather let a plant die and find something else that would thrive instead of getting into the chemical/trying to control nature thing. Just the way I roll. If it can't thrive on its' own after whatever coddling I can provide the first year, there are plenty of plants that can and will. So ignore me if that's horrifying to you, I won't mind.

There are some plants that are simply genetically predisposed to certain problems....no matter what. Keeping them as healthy as possible allows them to recover faster! And I'm all for yanking any plant that becomes a major disease or insect problem.

One of the many steps in Integrated Pest Management, and my personal favorite, is to practice wise plant selection. I've avoided bringing plants with known susceptibilities into my or my clients' properies. That kind of research us easy to do, no matter what kind of plant.....tree, shrub, veggie, annual, or perennial.

If I had a customer who really and truly wanted a gardenia (who can blame them), I gave them a bottle of horticultural oil as a gift.

By following good practices and smart plant selection, we can avoid to a great extent some serious problems. Then, should something become overwhelmed anyway....OFF WITH THEIR HEADS, is my motto.

LOL! Thanks! Beats painting the roses red.