My yucca plant gets very nice flower spikes which quickly become infested with aphids?

Ladybugs work wonders.

Not only are Aphids born pregnant, they're pregnant without benefit of sex. Not that sex with an aphid sounds like much of a treat. Two things are at work here: parthenogenesis and paedogenesis.

Parthenogenesis, also known as virgin birth, is rare in humans (one known case) but common in insects. The baby bugs, all of which are female, develop from single cells in mom's body. The advantage of this is that reproduction is very quick--none of this flowers and perfume jive--which helps when you've got as many natural enemies as aphids have.

Paedogenesis--pregnancy in the young--speeds up the process even more. "Although the young are not born until the aphid has reached the adult stage," it says here, "their development may begin before she is born while she is still in the ducts of the grandparental generation." Aphids can give birth ten days after having been born themselves. The baby showers must be murder.

Aphids are commonly covered in aphids, but if it isn't causing a problem, don't bother. Blasting them off with a strong stream of water from the hose works about as well as anything. Soapy water also works but may soap burn the bloom.....do it before the flowers open. Also horticultural oil sprayed on the unopened buds works well as it smothers the buggers. I wouldn't bother with anything stronger. I've been known to squish the guys when I can reach the infested area (depends on yucca species) Often there are predators among the aphids trying to help you and your control measures will also do in the predators......which is why I usually let the aphids stay as they really aren't causing that much problem.....and feeding some hummingbirds too.

Yes, lady bugs are the best. Also, control your ant population. They protect aphids because they drink a nectar like excrement that ants love especially in drought conditions. Once I got my ant population down, I haven't had an infestation. And, lady bugs are a highly protected animal in my garden. No one is allowed to do anything to them!

Since I don't use chemicals, I have an abundance of all kinds of insects. Praying mantis are also protected. My kids get scolded if they harm anything but a roach or a june bug (I hate those! lol)

I have to call zoos and colleges to find out what is in my garden sometimes. It's great.

Good luck!