Most garden centers and hardware/big box stores will have products that you need.
Generally, we are talking about insecticidal soap or horticultural oil, but there are other ways to gain control of pests in your garden as well.
Knowing more about the crop and it's most common problems is helpful, and our pages can help you know other, non-chemical management techniques like the use of floating row covers or hand removal.
See here for our crops page on greens: https://extension.umd.edu/hgic/topics/lettuce and https://extension.umd.edu/hgic/topics/salad-greens
and here for blueberries: https://extension.umd.edu/hgic/topics/blueberries
Remember you can always ask us questions and send us photos anytime during the growing season.