My kale and broccoli's are getting infested with aphids and they seem to be multiplying. I have tried to hose them off and that works temporarily but they are back in a few days. Research suggests using lady bugs is very effective. If someone has used it successfully, can they share some information such as how many lady bugs would I need, how effective was that, how do I keep them in my open backyard vs them flying off or better yet how do I multiply my lady bug population so they I have a good number year after year (or do I need to bring in lady bugs every year)
Ladybugs like to eat two things - some insects and pollen, so if you can plant around and about with plants that they'll like, that should help to not only attract them, but keep them around, so long as you've got something in flower for them. Not sure what the temperatures are like where you are, but in the UK, finding things ladybugs like that are in flower this early in the year is a bit difficult, but they like Chives, fennel, dill, English marigold (Calendula) and Tanacetum (feverfew) when they are in flower. With regard to Calendula, blackfly like those, so to some extent they can be used as a sacrificial plant because the aphids may prefer those to your food plants - Tropaeolum (Nasturtium) is another plant aphids love. Don't choose double flowered varieties to attract ladybugs, and pick plants with more open, flattish flowers. More suggestions can be found here: Tips To Attract Ladybugs To Your Garden.
Don't want to disuade you from trying but when a problematic bug explodes in number, they will never be quickly eradicated with a predator bug. Better to attend to conditions that caused the aphid outbreak. Without plentiful other sources of food for ladybugs and other conditions, they don't hang around. In any case, they will not effectively clean up aphids enough. Ladybugs show up naturally.
Typical causes for overabundance of aphids is overfertilization with high N fertilizers and/or extended wet cool weather.
Aphids like many insects go for the weakest plant they can see. So, if you have a raised bed of differing plants, you'll find that the aphids will target the weak plants and leave the strongest alone.
So, in my mixed raised of bed of cauliflowers, and broccoli, the broccoli are untouched but the cauliflowers are infested with aphids and cabbage worms ( I had an insect net but I guess the white butterfly somehow crawled under gaps ). Insects can detect abnormal growth patterns eg. excessive nitrogenous growth and that is like a blazing neon sign for them to come and feast.