If your lawn is clean and healthy, this prevents or reduces that chance of diseases from spreading or even surviving because of the proper clean-up that was done prior, making it free of contaminants and their ilk. When your lawn is cleaned-up after winter, this would make way for healthier plants all around. To properly prevent and reduce the spread of possible diseases, ensure that you cut any plants that you think has disease problems and clean the leaves fallen from it. Cut and dispose of those disease-ridden plants outside of the residence and not in your compost, else it would just spread throughout the surviving plants because it can survive in home compost piles. It’s always better to just hire a professional because they know best what to do.