I dont really do foliar sprays because I dont really veg my plants and I always have plants that are budding around my plants that are vegging (both rooms are on 12/12). I should take the time to take them outside of the room and spray the younger plants but there is a bit of laziness involved. I will foliar spray a little bit on my babies through the winter though because I am home full time and I will often have a compost tea brewing.
Compost teas are wicked and they work best in an all organic environment but for foliar spraying, they are great all around. You basically spray microbes/nutrients on the leaves and it protects them from pest and disease and make them grow stronger/healthier.
In the summer I was using a sprayer similar to this one
http://www.homedepot.ca/product/ms20h-handheld-sprayer/934920 to foliar spray my veggie garden, it works amazingly well, a little will go a long way and cover the leaves very well.
Additional info about compost teas:
If you were to start brewing compost tea for foliar feeding, most likely you would also want to use it to feed your plants. I do not want to point you in the wrong direction so you would have to research how well compost tea would work with flora nova. From what I remember, flora nova might not be certified organic but it is all about keeping the soil food web alive unlike most chemical fertilizer. If that's the case, they would work great together. If you have some time to kill I would strongly recommend reading the first post in this sticky:
https://www.rollitup.org/organics/427826-soil-food-web-gardening-compost.html
I am just getting into compost teas and they are fascinating and will help you grow wicked dank if you learn how to make it and use it properly. Its all about keeping the soil alive and roots happy...
Happy growing girls