Very good site that discusses identification, treatment and prevention of black leaf spots:
A more generic site that covers a wider range of weeping willow problems:
Hi Darlene, hope this helps you
Hello.Additionally for the best local professional advice
I would highly suggest contacting your cooperative extension. These offices are manned by volunteer master gardeners on site there waiting to answer the communities questions that know your local situation quite well.
Bringing a specimen of your tree —like a branch cutting with visible spots will help them identify the problem, if it can’t be diagnosed immediately it be sent to the local university for diagnosis and treatment recommendations.
Master gardeners are required to volunteer back
designated hours ( plus continuing education) each year to maintain MG certification -this community outreach and education is their goal.