Web Master:
Mulberries are renowned for fruit drop - its the one drawback of an otherwise excellent tree, especially as the dropped fruit can make quite a mess. This is due to a variety of environmental factors so its impossible to be precise. The most common reason is inconsistent water access - so ensure it gets plenty of water regularly especially from spring through to autumn. The next is just too much tree to support - which could be your problem Steve and the solution is a good pruning (winter being a good time). Essentially the tree just cant produce enough energy to support all the branches, leaves and fruit so it goes into survival mode and looks after itself first, the fruit second. Adequate pollination is another cause - the solution being planting other bee attracting plants near-by to encourage optimum pollination. Another reason can be weather - too much wind in particular can deter them from their fruit making duties. Too hot or cold can also be a factor - if too cold then a hessian cover over coldest nights is a solution - though in your case Steve its clearly too big for that. I'd suggest pruning is a first step followed be ensuring consistent water as a second step.