I had a leaf brocolli over-winter and go to seed, but lately I have seen just a few clusters of some gray infestation. They clumps are mostly on the outermost tips, but sometimes ikn a "crotch" or node.
The clumps are quite dense and clumpy as if fairly big gray and gray-white bugs all climbed up the branch to the highest spot until they were shoulder-to-shoulder. Or it looks a little like a clump of bumpy bird dung.
They are easy to brush off with a twig, and what's left behind looks wet, perhaps with sucked-out plant juice.
I cut the tips off and throw them into a sealed rubbish can. Only a tiny amount of the plant iks affected, but I want it to stay healthy until I can harvest thehuge amount of seed it promises.
The big plants are now almost entirely pods and stems and branches: just a few small leaves are left lower down.
The plant is Brassica oleracea var. 'Spigariello' . ("Spigariello Liscia" or "Broccolo Spigariello"). It was supposed to be an annual, but I saw NO pods all last summer or winter. It looked happy all winter (supposed to be hardy down to 25 F). This spring it started growing again, then threw out a million pods.
Can't help with ratios. I've never used it as a spray myself...I use it strait on a Q-tip before trhe numbers can grow, or use insecticidal soap. If no one else chimes in, you will find a lot of references on this forum, if you scan a bit.
I don't believe "dishwashing liquid" is much more than a "spreader/sticker", as most kinds are not soap, but detergent. It's the fatty acids in soap that get through the waxy coating on the bugs. Always worth trying what you have on hand though.