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What am I doing wrong with my Crepe Myrtles?

Posted: Sat Feb 27, 2010 8:52 pm
I am so frustrated with my Crepe Myrtles, it has forced me to join a forum! :D I will keep this as short as possible but will include all the details to hopefully help out with answers.
Here is my problem...I live in Central California, which gets very hot and somewhat dry summers. I have 2 CM trees and 5 CM bushes planted in the back yard, all in full sun. They are all quality CM's, bought at a local nursery about 8 years ago. I prune them every year, they are provided plant food throughout the year etc. etc. Every year, during the summer, all of the CM (along with my Rose of Sharon bushes) get completely overwhelmed with aphids. There have been several years where the aphids are SO thick that the flowers never open. I have tried about every type of aphid killer sprays there is and it does very little. What really gets me is my neighbor bought 4 CM trees about 3-4 years ago and has done NOTHING to them! No pruning, no plant food, no aphid killer....nothing. They get no aphids and look like other CM trees that are 30 years old. They are huge and beautiful. As I walk the neighborhood in the summertime, I never see any other CM's with such aphid problems. Someone told me not to prune them, so I didn't for that year, and that didn't help. Another person told me you have to prune them really far down, kind of like roses. I tried that too, and it did nothing.
So why are my CM's aphid magnets? And why do my neighbors do so great with no care at all? And last but not least, what is the correct way to prune them? Down to the nubs or just mild pruning?
Sorry about being so long here guys. Thanks for any help!

Posted: Sat Feb 27, 2010 9:42 pm
by Kisal
You might check for ants. Ants often carry aphids onto plants. The ants like the honeydew the aphids produce, and take care of the aphids in return, i.e. making sure the aphids are on the softest, juiciest parts of the plants.

You could release some ladybug beetles on your crepe myrtles. They are natural predators of aphids. :)

By trying to kill the aphids, you may inadvertently also be killing the natural predators, as well, allowing for a population explosion among the aphids.

Posted: Sun Feb 28, 2010 3:23 am
Thanks Kisal...I had no idea ants and aphids had that kind of relationship. John

Posted: Sun Feb 28, 2010 8:41 am
by JONA878
If the problem persists JP you can buy aphid specific insectacides.
They are more expensive but they will allow the 'goodies ' on your plants to live on.
One other thing that might help is to put a grease band around your plant.
This will stop the ants from climbing up and take away the aphids protectors.


Posted: Sun Feb 28, 2010 1:13 pm
by rainbowgardener
Absolutely agree with Kisal. Welcome to the wonderful world of chemistry! By using insecticides, you kill off all the ladybugs, lacewings, praying mantises, parasitic wasps and other predators of the aphids. So the aphids disappear for a few days and then come zooming right back in more numbers than ever, with no biological controls left.

This thread has a whole bunch on organic control of aphids:

You can buy ladybugs for release in your garden. That would be your first line of defense. You can reduce the population of aphids just by washing them off with a good hard stream of water and/or going over the shrub with a paper towel and squishing them. I have a honeysuckle trumpet vine that gets covered with aphids every spring. I just squish them and they don't come back.

Also put out bird feeders! Lots of birds that come to the feeders will also eat the aphids.

Bear in mind you never want to get down to zero aphids, because then all the ladybugs will leave! If your plant is healthy, a little bit of aphids won't hurt it. The difference between your CM's and your neighbors may be in how healthy the plants are. Insects prey on the most vulnerable plants. Part of that is that it sounds like you may be over-pruning. They don't need a lot of pruning and none at all is probably better than too much.

Here's a little article about pruning CM:

Posted: Sun Feb 28, 2010 6:37 pm
Thanks everyone! A few things I'll do differently this year...I will not be pruning, ladybugs, and I will be going with an organic spray rather than a insecticide. I have a good feeling about this!