Usually right around the time you're pruning is also the perfect time to do dormant oil spraying. Ideally do your pruning first as you'll use less spray, your tree will be more open AND you can spray all those new cuts you made to keep anything out of them!
Choose a nice warm sunny day. This will allow the spray to dry and coat the tree better. Avoid spraying if it's going to rain in the next day or two as it will just wash off, and avoid high winds as it will be harder to control.
The reason to spray is to control multiple different pests and diseases that might be on your trees over the winter.
Recently I've been using a larger volume back-pack type sprayer and this thing is a dream, but I also have probably 20 pretty large trees I'm spraying. You can probably get buy just fine with a simple pump type with a hand spraying wand if you have a few trees. It can be a bit awkward to carry and spray higher into the trees and I felt I was constantly pumping it. I definitely should have upgraded sooner and if you're avoiding spraying cause you hate your pump sprayer (like I did) then get the backpack. If you only have a single tree you can also get by with a dollar store spray bottle or clean out an old windex sprayer and use that.
Another tip is to be sure to clean it well and spray some water through when you're done or it can get pretty clogged up and messy. When you do dismantle it to clean it, find a nice clean space (not in the grass of the orchard) as it seems to have a a lot of tiny pieces that like to spring and launch away.
The Dormant Oil
So the "dormant oil" isn't actually one specific thing. You are spraying the "dormant" tree with "oil". Most often people use a mix of lime sulfur and horticultural oil, you mix with water and spray. The lime sulfur can give you a bit of added fungicidal coverage than just using an oil based spray, but then it is a chemical you are adding to your garden. It is considered and approved for "organic" gardens and most recently I have been using it regularly.
If you prefer you can also make your own simply with 1 cup vegetable oil, 2 tablespoons of dish soap and 1 gallon of water and mix it well in your sprayer. There are all kinds of other concoctions that include peroxide or baking soda and different people recommend different types or soap and oils. Feel free to do a quick google search of your other options.
Whatever you prefer to use I do strongly recommend spraying with something, especially as you start getting more trees. Don't underestimate how fast a pest or fungal problem can get out of hand and how devastating it can be, and this simple prevention step is strongly encouraged.
