Brown Spots on weeping mulbery leaves
This looks like Cercospora leaf spot. And perhaps some anthracnose, another fungal disease. This year’s cool wet start has been ideal for leaf spot diseases.
This article from Purdue Extension describes what to do-
“Leaf Spot of Mulberry
Tom Creswell, Plant Disease Diagnostician and Director, Plant & Pest Diagnostic Lab
Fungal leaf spots on trees can cause yellowing and premature leaf drop, as seen here on Mulberry. This leaf spot is fairly common on Mulberry but causes more noticeable damage on trees with poor air movement, growing in shady conditions or older trees with less vigorous summer growth. However some trees are infected repeatedly, even when growing in full sun. Fungicides are not necessary because the fungus doesn't cause serious harm to the overall health of the tree. Fallen leaves should be raked and removed from the area to help reduce the amount of fungus present next spring when new growth starts.“
If your client wants to use a fungicide, and wants to eat the fruit from the tree, he must use a fungicide labeled for fruit trees. A fungicide spray next spring as the buds begin to swell (during wet weather) and repeated according to the label while the weather is wet, will help reduce leaf spot diseases. Thank you.