Leaf drop early in the season can be quite alarming!  Just when the tree should be coming into its most full lush growth it suddenly drops large quantities of leaves.  And raking leaves is just NOT what spring is all about! 

Fortunately, even though the leaf drop causes a great deal of concern it is rarely anything that causes harm to the tree.  There are two major reasons for leaf drop in maples (and other trees) and the prescribed cure for both is the same:  Do NOTHING.  The tree will form new leaves, have a healthy summer and drop them again at the normal time in the fall.  Here is what is happening:

A tiny non-native sawfly called Maple Petiole Borer lays its eggs on the maple leaf petiole (the petiole is the skinny stem that attaches the leaf to the branch).  The eggs hatch and the larva invade the petiole where they feed.  At some point the petiole is so weakened that it breaks and the leaf drops.  Eventually the entire petiole will fall, the larva will leave the petiole, burrow into the ground and the following spring a new generation of sawflies will emerge.  There is only one hatch per year so after the leaves drop no new sawflies will bother the tree until the next spring.  There is plenty of time for the tree to recover, form new leaves and complete its season of growth. 

The other main reason for spring leaf drop is Anthracnose, which infects maples and some other trees.  This is a fungal disease that thrives in cool, damp spring weather.  It primarily infects newly emerging leaves.  Therefore, as the remaining leaves mature and the weather warms the fungus is less able to cause problems.  New leaves continue to emerge and the tree goes on about its business.

Look at some of the dropped leaves.  Do they look relatively healthy and have a portion of their stem or petiole attached?  You have the Maple petiole borer.  Or, do they have dark spots of dead tissue or deformed leaf portions?  Probably Anthracnose.  Either way, by the time the leaves drop the problem is past the point where treatment would be effective.  Even preventive treatment is not recommended because the tree will do just fine without it.

Here are links to several websites with information about Maple Leaf Petiole Borer (and good pictures) and about Anthracnose.  One is from Ohio State University, one from Michigan State University and one from the University of Minnesota.  Obviously, these problems are widespread. 

http://msue.anr.msu.edu/news/maple_petiole_borer_causing_leaf_drop_in_maple_trees

http://bygl.osu.edu/node/735

http://blog-yard-garden-news.extension.umn.edu/2016/05/spring-leaf-drop-and-anthracnose.html

I read of one other cause for early leaf drop – it seems that even trees with no problems at all drop leaves in the spring.  It turns out they are so excited to get growing again that they put out far more leaves during the cool wet spring than the tree can support in the hot dry summer.  So, they drop some.   

One thing that bothered me.  You wrote that your tree dropped ALL its leaves in June.  The research mentioned trees shedding a lot of leaves or a few bags full of leaves.  They did not say ALL.  If your tree is really losing 100% of its leaves it is possible there could be something more going on.  If you are still concerned, by all means have your tree examined by an ISA certified arborist.  Search on-line or contact your local extension office if you need help finding one.  Here is the contact information for Franklin county Extension:

530 West Spring Street, Suite 275
Columbus, Ohio 43215

Phone:<personal data hidden>

Thank you for your query and good luck!