Dwarf means weak and the weakness means less margin for error. Dwarf trees are low energy to begin with and when they are further staggered by insects and/or disease they can absolutely stop growing and be difficult to return to vigor which is what has to happen for the trees to be productive.

If you search this site for info about spray regimen I'm sure you can find the necessary info, besides what you need to know about fertilizing the trees and keeping away competition from weeds and grass and, oh yeah, whether the soil is adequately drained and so forth.

If you are successful at other kinds of gardening, much of this is probably already handled by you but fruit trees are challenging as a first endeavor in the soil.