If you are a nursery or garden center most likely you will already have some products that you can use for your blueberry plants. Blueberry plants like acidic soil much like azaleas, rhododendrons, and Japanese maples. When fertilizing there is a common product that miracle grow provides called miracle grow for acid loving plants. This can be applied as soon as the leaf buds reach 1/4 inch. After the first application it can be applied every two weeks until the berries start to from. Once all the berries are either picked or all fall off you can continue fertilizing every two weeks until the middle of august. Once it is the middle of august all fertilizing should stop.
For fungus there is a product that can be bought on amazon either diluted or ready to go in a spray bottle called serenade. Read instructions for how to use. Fungus is generally a problem if it is a hot rainy summer.
We are not held responsible if you use these products and your blueberry plants do not perform well or die.