Many diseases, and some insects, that attack fruit trees during the summer will overwinter on or under the tree. Fruit that is left on the tree or allowed to rot under the tree often carry fungi that will affect next seasons crop. Even leaves left under the tree can be a source of diseases the next growing season.
Often times fruit left on or around the tree will not rot completely. These fruit will shrivel up into a small ball and are called mummies. Although they may look dry and harmless these mummies will produce fungal spores during the spring and summer that can infect new fruit. Brown rot on peaches and summer rots on apples can quickly spread and may be uncontrollable, even with fungicide applications.
The same is true for leaves left around the tree. In previous posts I have mentioned a disease called scab on apples. This fungus will invade leaf tissue and fruit which may cause defoliation and substandard fruit. Leaves on the ground near the tree are a primary source of scab spores during the spring of the year.
Cleaning up the mummies and old leaves will greatly reduce the source of these fungi and help in disease control. Old fruit should be removed from the area and destroyed. Old leaves can either be removed or shredded by mowing to hasten leaf decomposition. Either way, sanitation is an important step in managing diseases for the upcoming season.