Many here prefer non-chemical solutions. A thorough, strong spray of water knocks most of them off, almost totally if repeated for several days. Also, natural preditory insects LOVE to munch on aphids, so this technique does no harm to those that will help the problem naturally.
hortster

Totally agree with hortster. Also, aphids don't like extreme heat so they generally become less of a problem as we get into summer.

Oh dear...there are so many Crape myrtle hybrids that are resistant to aphids. Those are not only aphids, but the Crape myrtle aphid, Tinocallis kahawaluokalani.

Something that you should do this coming winter is spray your tree a couple of times with a horticultural oil, even a dormant oil. Oil applications can do wonders to nip the aphid cycle in the bud by smothering eggs. Spray bare branches thoroughly.

What kind of Crape Myrtle is this, if you don't mind me asking?

It's a Catawba.

I've been spraying with water, starting today. The tree is about 3.5' tall, so it's in a pretty fragile stage after it's transplant. I accidentally hit it with a high pressure and knocked off a good few leaves, but I figured out a setting on the nozzle that does a better job. I'm spraying about 3 times per day and I hope that handles most of the problem. It's impossible to get all of them.

Is there a certain type of insect that I should buy if this problem persists? I know the greenhouse at school uses predation of this sort, but I didn't know how effective it would be in an outdoor setting such as this. I know they buy them by the tube and release them.

From my research the Catawba was a fairly disease and mildew resistant hybrid, but I didn't even look into aphid resistance when I chose the plant.

I find that the best way to use the hose to get rid of aphids is to take off the nozzle and use my thumb over the opening to create a fan spray. It will be easy on the plant but hard on the aphids. You also have to direct the water sprays at the aphids.

You can also add a commercial insecticidal soap to your routine, and if conditions are right (like after the sun goes down), an application of Neem oil. Please don't forget the use of a dormant season application of horticultural oil. I keep Volck Oil on hand for winter spraying. It will truly make a difference.

Using any kind of predator insects for ONE little tree would not be a worthy use of your money. Perhaps some ladybugs (and other predators and parasites) will find your tree on their own.

Can we see a picture of the whole tree?

I have a nozzle specifically designed for knocking the pests off the plants that I use in my greenhouse (where the bugs come in to get out of the elements!) It's called the Bug Blaster. Best method that I've come up with. Take a look. I seldom bother to take it outside as I don't have many bug problems in the garden, but the photos sure make it look like it would work on larger plants as well.

Here is a link that might be useful: The Bug Blaster

What about a systemic insecticide like Bayer Advanced (the liquid form, not the granules) that's poured at the base of the plant over the root bed, taken up & protects for a very long time? Would that kill them?

I'd get tired of the bother of repeated spraying, unless a time or two would do it.

Richard.

That bug blaster may be the key to this. I sprayed religiously for a few days, and got most of them, but apparently not all and they are back in force. The issue is getting to the bottom of the leaves. This is a tiny new tree (4 feet), and I still don't have the time or patience to spray the bottom of the leaves. The only way I can get to them with a traditional nozzle is to flip the leaves by hand...no way.

My parents recommended 7 Dust?

Rhizo, I tried to take a picture of the entire tree but my phone is acting up and won't take photos. It's a very small tree as I just planted it this past winter. It is about 4 feet tall.

How does such a small tree cost hundreds of dollars to replace? I'm curious about that.

Sad to say but any plant that is a "magnet " for a particular pest or disease will retain that predisposition for its life. There are cultural and chemical measures you can take....every year (several times a year) but you'll battle the problem always.

Sevin is not the way to go. Aphids are prey to a host of predatory and parasitic critters. Sevin will kill all of them, too. This often results in a serious population explosion of an assortment of pests.
Sevin is also extremely toxic to bees.

Speaking of bees and all other pollinators, systemic insecticides enter the vascular system of plants, tainting pollen and nectar.

There are other, softer, pesticides you can try. Horticultural oils (as mentioned earlier) can be extremely helpful. These would include Neem oil which acts as an anti -feedant, insect growth regulator, as well as physically smothering overwintering eggs and living aphids.

I have a small pump sprayer with a separate nozzle attachment that directs spray UP. It allows me to hold the wand down at the base of the plant, while the product I'm spraying covers the underside of the foliage.

If I were you? I'd do all I could do to control aphids with the least toxic means possible. If you begin seeing black sooty mold all over the leaves and branches, you're losing the battle. Avoid excess fertilization with high nitrogen products; this plant is not a heavy feeder. If, after a year or two, you are still battling a constant battle.....OFF WITH ITS HEAD!

You don't have to buy predatory insects- they will show up on their own as long as the environment remains non-toxic and amenable to them. When I ceased using any sort of chemicals back in '96 I found an amazing number of biological control critters began to reappear in my gardens.
By using chemicals I had destroyed the population of good guys more than getting rid of the bad.
It is a vicious cycle and you have to learn let go of "controlling" everything and let nature do it's thing.

If it was me I would use water, insecticidal soap if it got really bad, and horticultural oil during dormancy.
If I could not control it that way then I would let the plant sink or swim on its own and if it sank I would make damn sure I chose a replacement wisely.
What I would not do is pollute my property with a substance that drove away the good insects.

But I am pretty sure it would not sink- minus any control the aphids would get really really bad, the plant would look like doody, but at about that point the predatory insect brigade would sweep in and put the situation back in balance.

And balance is what I strive for- balance means allowing predatory insects to live and do their thing while also accepting the odd pest and cosmetic damage. The pendulum may swing toward more pests then to less pests but eventually will settle somewhere in the middle and a happy medium will be the long term result.

Very good advice from cearb! I might add that the tree is already exhibiting black sooty mold.

drrich2 wrote "What about a systemic insecticide like Bayer Advanced (the liquid form, not the granules) that's poured at the base of the plant over the root bed, taken up & protects for a very long time? Would that kill them?"

Yes, it works very well on all types of sucking insects, aphids, scale, mealybugs, whitefly. And it generally does provide season-long protection. I use it routinely on my potted plants and as needed on in-ground plants.

I have many hundreds of wasps in one of my crape myrtles. I don't know when to try the spraying of leaves with water as I am scared of getting stung. My cars are now covered with a sticky substance as well since they are near this tree.

Yeah, the wasps were my first clue last year that something was wrong ... I thought they were nesting in the bushes, there were so many, but I assume now that they were feasting on the aphids.

Thanks for all of the good tips, everyone!

There is one thing that has been missed but it depends on where you live. If you live in one of the southern states like the Carolinas, stop using pesticides and develop an environment that promotes lizards, Skinks, anoles, etc.

You would be surprise at the number of insects they will eat in a very short time. If you are careful to get a small one you can even use them to keep your inside plants clean.. You will not even know they are there. We have some tropicals that can not take the Carolina winters. I don't know how many times during the winter we have discovered we have a lizard in the house.

Please, remember that any systemic chemical application that is poured for uptake into the plant or tree is toxic to ALL insects and that includes bees, etc.